Vendor golang's go/types to include a fix for CGo typechecking.

third_party/BUILD

@@ -18,6 +18,7 @@ filegroup(
         "//third_party/forked/etcd237/pkg/fileutil:all-srcs",
         "//third_party/forked/etcd237/wal:all-srcs",
         "//third_party/forked/golang/expansion:all-srcs",
+        "//third_party/forked/golang/go/types:all-srcs",
         "//third_party/forked/golang/reflect:all-srcs",
         "//third_party/forked/golang/template:all-srcs",
         "//third_party/forked/gonum/graph:all-srcs",

third_party/forked/golang/go/types/BUILD

+licenses(["notice"])
+
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = [
+        "api.go",
+        "assignments.go",
+        "builtins.go",
+        "call.go",
+        "check.go",
+        "conversions.go",
+        "decl.go",
+        "errors.go",
+        "eval.go",
+        "expr.go",
+        "exprstring.go",
+        "initorder.go",
+        "labels.go",
+        "lookup.go",
+        "methodset.go",
+        "object.go",
+        "objset.go",
+        "operand.go",
+        "ordering.go",
+        "package.go",
+        "predicates.go",
+        "resolver.go",
+        "return.go",
+        "scope.go",
+        "selection.go",
+        "sizes.go",
+        "stmt.go",
+        "type.go",
+        "typestring.go",
+        "typexpr.go",
+        "universe.go",
+    ],
+    importpath = "k8s.io/kubernetes/third_party/forked/golang/go/types",
+    visibility = ["//visibility:public"],
+)
+
+filegroup(
+    name = "package-srcs",
+    srcs = glob(["**"]),
+    tags = ["automanaged"],
+    visibility = ["//visibility:private"],
+)
+
+filegroup(
+    name = "all-srcs",
+    srcs = [":package-srcs"],
+    tags = ["automanaged"],
+    visibility = ["//visibility:public"],
+)

third_party/forked/golang/go/types/README

+This is go/types forked from go@236abdb46b (just after 1.10) and cherry-picked
+1006f703ffc, which fixes https://github.com/golang/go/issues/23712.
+
+It can be removed when all builders are >= go1.11.
+
+Do *not* update this to newer code if https://github.com/golang/go/issues/23914
+has not been fixed!

third_party/forked/golang/go/types/api.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package types declares the data types and implements
+// the algorithms for type-checking of Go packages. Use
+// Config.Check to invoke the type checker for a package.
+// Alternatively, create a new type checker with NewChecker
+// and invoke it incrementally by calling Checker.Files.
+//
+// Type-checking consists of several interdependent phases:
+//
+// Name resolution maps each identifier (ast.Ident) in the program to the
+// language object (Object) it denotes.
+// Use Info.{Defs,Uses,Implicits} for the results of name resolution.
+//
+// Constant folding computes the exact constant value (constant.Value)
+// for every expression (ast.Expr) that is a compile-time constant.
+// Use Info.Types[expr].Value for the results of constant folding.
+//
+// Type inference computes the type (Type) of every expression (ast.Expr)
+// and checks for compliance with the language specification.
+// Use Info.Types[expr].Type for the results of type inference.
+//
+// For a tutorial, see https://golang.org/s/types-tutorial.
+//
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+// An Error describes a type-checking error; it implements the error interface.
+// A "soft" error is an error that still permits a valid interpretation of a
+// package (such as "unused variable"); "hard" errors may lead to unpredictable
+// behavior if ignored.
+type Error struct {
+	Fset *token.FileSet // file set for interpretation of Pos
+	Pos  token.Pos      // error position
+	Msg  string         // error message
+	Soft bool           // if set, error is "soft"
+}
+
+// Error returns an error string formatted as follows:
+// filename:line:column: message
+func (err Error) Error() string {
+	return fmt.Sprintf("%s: %s", err.Fset.Position(err.Pos), err.Msg)
+}
+
+// An Importer resolves import paths to Packages.
+//
+// CAUTION: This interface does not support the import of locally
+// vendored packages. See https://golang.org/s/go15vendor.
+// If possible, external implementations should implement ImporterFrom.
+type Importer interface {
+	// Import returns the imported package for the given import path.
+	// The semantics is like for ImporterFrom.ImportFrom except that
+	// dir and mode are ignored (since they are not present).
+	Import(path string) (*Package, error)
+}
+
+// ImportMode is reserved for future use.
+type ImportMode int
+
+// An ImporterFrom resolves import paths to packages; it
+// supports vendoring per https://golang.org/s/go15vendor.
+// Use go/importer to obtain an ImporterFrom implementation.
+type ImporterFrom interface {
+	// Importer is present for backward-compatibility. Calling
+	// Import(path) is the same as calling ImportFrom(path, "", 0);
+	// i.e., locally vendored packages may not be found.
+	// The types package does not call Import if an ImporterFrom
+	// is present.
+	Importer
+
+	// ImportFrom returns the imported package for the given import
+	// path when imported by a package file located in dir.
+	// If the import failed, besides returning an error, ImportFrom
+	// is encouraged to cache and return a package anyway, if one
+	// was created. This will reduce package inconsistencies and
+	// follow-on type checker errors due to the missing package.
+	// The mode value must be 0; it is reserved for future use.
+	// Two calls to ImportFrom with the same path and dir must
+	// return the same package.
+	ImportFrom(path, dir string, mode ImportMode) (*Package, error)
+}
+
+// A Config specifies the configuration for type checking.
+// The zero value for Config is a ready-to-use default configuration.
+type Config struct {
+	// If IgnoreFuncBodies is set, function bodies are not
+	// type-checked.
+	IgnoreFuncBodies bool
+
+	// If FakeImportC is set, `import "C"` (for packages requiring Cgo)
+	// declares an empty "C" package and errors are omitted for qualified
+	// identifiers referring to package C (which won't find an object).
+	// This feature is intended for the standard library cmd/api tool.
+	//
+	// Caution: Effects may be unpredictable due to follow-on errors.
+	//          Do not use casually!
+	FakeImportC bool
+
+	// If Error != nil, it is called with each error found
+	// during type checking; err has dynamic type Error.
+	// Secondary errors (for instance, to enumerate all types
+	// involved in an invalid recursive type declaration) have
+	// error strings that start with a '\t' character.
+	// If Error == nil, type-checking stops with the first
+	// error found.
+	Error func(err error)
+
+	// An importer is used to import packages referred to from
+	// import declarations.
+	// If the installed importer implements ImporterFrom, the type
+	// checker calls ImportFrom instead of Import.
+	// The type checker reports an error if an importer is needed
+	// but none was installed.
+	Importer Importer
+
+	// If Sizes != nil, it provides the sizing functions for package unsafe.
+	// Otherwise SizesFor("gc", "amd64") is used instead.
+	Sizes Sizes
+
+	// If DisableUnusedImportCheck is set, packages are not checked
+	// for unused imports.
+	DisableUnusedImportCheck bool
+}
+
+// Info holds result type information for a type-checked package.
+// Only the information for which a map is provided is collected.
+// If the package has type errors, the collected information may
+// be incomplete.
+type Info struct {
+	// Types maps expressions to their types, and for constant
+	// expressions, also their values. Invalid expressions are
+	// omitted.
+	//
+	// For (possibly parenthesized) identifiers denoting built-in
+	// functions, the recorded signatures are call-site specific:
+	// if the call result is not a constant, the recorded type is
+	// an argument-specific signature. Otherwise, the recorded type
+	// is invalid.
+	//
+	// The Types map does not record the type of every identifier,
+	// only those that appear where an arbitrary expression is
+	// permitted. For instance, the identifier f in a selector
+	// expression x.f is found only in the Selections map, the
+	// identifier z in a variable declaration 'var z int' is found
+	// only in the Defs map, and identifiers denoting packages in
+	// qualified identifiers are collected in the Uses map.
+	Types map[ast.Expr]TypeAndValue
+
+	// Defs maps identifiers to the objects they define (including
+	// package names, dots "." of dot-imports, and blank "_" identifiers).
+	// For identifiers that do not denote objects (e.g., the package name
+	// in package clauses, or symbolic variables t in t := x.(type) of
+	// type switch headers), the corresponding objects are nil.
+	//
+	// For an anonymous field, Defs returns the field *Var it defines.
+	//
+	// Invariant: Defs[id] == nil || Defs[id].Pos() == id.Pos()
+	Defs map[*ast.Ident]Object
+
+	// Uses maps identifiers to the objects they denote.
+	//
+	// For an anonymous field, Uses returns the *TypeName it denotes.
+	//
+	// Invariant: Uses[id].Pos() != id.Pos()
+	Uses map[*ast.Ident]Object
+
+	// Implicits maps nodes to their implicitly declared objects, if any.
+	// The following node and object types may appear:
+	//
+	//     node               declared object
+	//
+	//     *ast.ImportSpec    *PkgName for imports without renames
+	//     *ast.CaseClause    type-specific *Var for each type switch case clause (incl. default)
+	//     *ast.Field         anonymous parameter *Var
+	//
+	Implicits map[ast.Node]Object
+
+	// Selections maps selector expressions (excluding qualified identifiers)
+	// to their corresponding selections.
+	Selections map[*ast.SelectorExpr]*Selection
+
+	// Scopes maps ast.Nodes to the scopes they define. Package scopes are not
+	// associated with a specific node but with all files belonging to a package.
+	// Thus, the package scope can be found in the type-checked Package object.
+	// Scopes nest, with the Universe scope being the outermost scope, enclosing
+	// the package scope, which contains (one or more) files scopes, which enclose
+	// function scopes which in turn enclose statement and function literal scopes.
+	// Note that even though package-level functions are declared in the package
+	// scope, the function scopes are embedded in the file scope of the file
+	// containing the function declaration.
+	//
+	// The following node types may appear in Scopes:
+	//
+	//     *ast.File
+	//     *ast.FuncType
+	//     *ast.BlockStmt
+	//     *ast.IfStmt
+	//     *ast.SwitchStmt
+	//     *ast.TypeSwitchStmt
+	//     *ast.CaseClause
+	//     *ast.CommClause
+	//     *ast.ForStmt
+	//     *ast.RangeStmt
+	//
+	Scopes map[ast.Node]*Scope
+
+	// InitOrder is the list of package-level initializers in the order in which
+	// they must be executed. Initializers referring to variables related by an
+	// initialization dependency appear in topological order, the others appear
+	// in source order. Variables without an initialization expression do not
+	// appear in this list.
+	InitOrder []*Initializer
+}
+
+// TypeOf returns the type of expression e, or nil if not found.
+// Precondition: the Types, Uses and Defs maps are populated.
+//
+func (info *Info) TypeOf(e ast.Expr) Type {
+	if t, ok := info.Types[e]; ok {
+		return t.Type
+	}
+	if id, _ := e.(*ast.Ident); id != nil {
+		if obj := info.ObjectOf(id); obj != nil {
+			return obj.Type()
+		}
+	}
+	return nil
+}
+
+// ObjectOf returns the object denoted by the specified id,
+// or nil if not found.
+//
+// If id is an anonymous struct field, ObjectOf returns the field (*Var)
+// it uses, not the type (*TypeName) it defines.
+//
+// Precondition: the Uses and Defs maps are populated.
+//
+func (info *Info) ObjectOf(id *ast.Ident) Object {
+	if obj := info.Defs[id]; obj != nil {
+		return obj
+	}
+	return info.Uses[id]
+}
+
+// TypeAndValue reports the type and value (for constants)
+// of the corresponding expression.
+type TypeAndValue struct {
+	mode  operandMode
+	Type  Type
+	Value constant.Value
+}
+
+// TODO(gri) Consider eliminating the IsVoid predicate. Instead, report
+// "void" values as regular values but with the empty tuple type.
+
+// IsVoid reports whether the corresponding expression
+// is a function call without results.
+func (tv TypeAndValue) IsVoid() bool {
+	return tv.mode == novalue
+}
+
+// IsType reports whether the corresponding expression specifies a type.
+func (tv TypeAndValue) IsType() bool {
+	return tv.mode == typexpr
+}
+
+// IsBuiltin reports whether the corresponding expression denotes
+// a (possibly parenthesized) built-in function.
+func (tv TypeAndValue) IsBuiltin() bool {
+	return tv.mode == builtin
+}
+
+// IsValue reports whether the corresponding expression is a value.
+// Builtins are not considered values. Constant values have a non-
+// nil Value.
+func (tv TypeAndValue) IsValue() bool {
+	switch tv.mode {
+	case constant_, variable, mapindex, value, commaok:
+		return true
+	}
+	return false
+}
+
+// IsNil reports whether the corresponding expression denotes the
+// predeclared value nil.
+func (tv TypeAndValue) IsNil() bool {
+	return tv.mode == value && tv.Type == Typ[UntypedNil]
+}
+
+// Addressable reports whether the corresponding expression
+// is addressable (https://golang.org/ref/spec#Address_operators).
+func (tv TypeAndValue) Addressable() bool {
+	return tv.mode == variable
+}
+
+// Assignable reports whether the corresponding expression
+// is assignable to (provided a value of the right type).
+func (tv TypeAndValue) Assignable() bool {
+	return tv.mode == variable || tv.mode == mapindex
+}
+
+// HasOk reports whether the corresponding expression may be
+// used on the lhs of a comma-ok assignment.
+func (tv TypeAndValue) HasOk() bool {
+	return tv.mode == commaok || tv.mode == mapindex
+}
+
+// An Initializer describes a package-level variable, or a list of variables in case
+// of a multi-valued initialization expression, and the corresponding initialization
+// expression.
+type Initializer struct {
+	Lhs []*Var // var Lhs = Rhs
+	Rhs ast.Expr
+}
+
+func (init *Initializer) String() string {
+	var buf bytes.Buffer
+	for i, lhs := range init.Lhs {
+		if i > 0 {
+			buf.WriteString(", ")
+		}
+		buf.WriteString(lhs.Name())
+	}
+	buf.WriteString(" = ")
+	WriteExpr(&buf, init.Rhs)
+	return buf.String()
+}
+
+// Check type-checks a package and returns the resulting package object and
+// the first error if any. Additionally, if info != nil, Check populates each
+// of the non-nil maps in the Info struct.
+//
+// The package is marked as complete if no errors occurred, otherwise it is
+// incomplete. See Config.Error for controlling behavior in the presence of
+// errors.
+//
+// The package is specified by a list of *ast.Files and corresponding
+// file set, and the package path the package is identified with.
+// The clean path must not be empty or dot (".").
+func (conf *Config) Check(path string, fset *token.FileSet, files []*ast.File, info *Info) (*Package, error) {
+	pkg := NewPackage(path, "")
+	return pkg, NewChecker(conf, fset, pkg, info).Files(files)
+}
+
+// AssertableTo reports whether a value of type V can be asserted to have type T.
+func AssertableTo(V *Interface, T Type) bool {
+	m, _ := assertableTo(V, T)
+	return m == nil
+}
+
+// AssignableTo reports whether a value of type V is assignable to a variable of type T.
+func AssignableTo(V, T Type) bool {
+	x := operand{mode: value, typ: V}
+	return x.assignableTo(nil, T, nil) // config not needed for non-constant x
+}
+
+// ConvertibleTo reports whether a value of type V is convertible to a value of type T.
+func ConvertibleTo(V, T Type) bool {
+	x := operand{mode: value, typ: V}
+	return x.convertibleTo(nil, T) // config not needed for non-constant x
+}
+
+// Implements reports whether type V implements interface T.
+func Implements(V Type, T *Interface) bool {
+	f, _ := MissingMethod(V, T, true)
+	return f == nil
+}

third_party/forked/golang/go/types/assignments.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements initialization and assignment checks.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// assignment reports whether x can be assigned to a variable of type T,
+// if necessary by attempting to convert untyped values to the appropriate
+// type. context describes the context in which the assignment takes place.
+// Use T == nil to indicate assignment to an untyped blank identifier.
+// x.mode is set to invalid if the assignment failed.
+func (check *Checker) assignment(x *operand, T Type, context string) {
+	check.singleValue(x)
+
+	switch x.mode {
+	case invalid:
+		return // error reported before
+	case constant_, variable, mapindex, value, commaok:
+		// ok
+	default:
+		unreachable()
+	}
+
+	if isUntyped(x.typ) {
+		target := T
+		// spec: "If an untyped constant is assigned to a variable of interface
+		// type or the blank identifier, the constant is first converted to type
+		// bool, rune, int, float64, complex128 or string respectively, depending
+		// on whether the value is a boolean, rune, integer, floating-point, complex,
+		// or string constant."
+		if T == nil || IsInterface(T) {
+			if T == nil && x.typ == Typ[UntypedNil] {
+				check.errorf(x.pos(), "use of untyped nil in %s", context)
+				x.mode = invalid
+				return
+			}
+			target = Default(x.typ)
+		}
+		check.convertUntyped(x, target)
+		if x.mode == invalid {
+			return
+		}
+	}
+	// x.typ is typed
+
+	// spec: "If a left-hand side is the blank identifier, any typed or
+	// non-constant value except for the predeclared identifier nil may
+	// be assigned to it."
+	if T == nil {
+		return
+	}
+
+	if reason := ""; !x.assignableTo(check.conf, T, &reason) {
+		if reason != "" {
+			check.errorf(x.pos(), "cannot use %s as %s value in %s: %s", x, T, context, reason)
+		} else {
+			check.errorf(x.pos(), "cannot use %s as %s value in %s", x, T, context)
+		}
+		x.mode = invalid
+	}
+}
+
+func (check *Checker) initConst(lhs *Const, x *operand) {
+	if x.mode == invalid || x.typ == Typ[Invalid] || lhs.typ == Typ[Invalid] {
+		if lhs.typ == nil {
+			lhs.typ = Typ[Invalid]
+		}
+		return
+	}
+
+	// rhs must be a constant
+	if x.mode != constant_ {
+		check.errorf(x.pos(), "%s is not constant", x)
+		if lhs.typ == nil {
+			lhs.typ = Typ[Invalid]
+		}
+		return
+	}
+	assert(isConstType(x.typ))
+
+	// If the lhs doesn't have a type yet, use the type of x.
+	if lhs.typ == nil {
+		lhs.typ = x.typ
+	}
+
+	check.assignment(x, lhs.typ, "constant declaration")
+	if x.mode == invalid {
+		return
+	}
+
+	lhs.val = x.val
+}
+
+func (check *Checker) initVar(lhs *Var, x *operand, context string) Type {
+	if x.mode == invalid || x.typ == Typ[Invalid] || lhs.typ == Typ[Invalid] {
+		if lhs.typ == nil {
+			lhs.typ = Typ[Invalid]
+		}
+		return nil
+	}
+
+	// If the lhs doesn't have a type yet, use the type of x.
+	if lhs.typ == nil {
+		typ := x.typ
+		if isUntyped(typ) {
+			// convert untyped types to default types
+			if typ == Typ[UntypedNil] {
+				check.errorf(x.pos(), "use of untyped nil in %s", context)
+				lhs.typ = Typ[Invalid]
+				return nil
+			}
+			typ = Default(typ)
+		}
+		lhs.typ = typ
+	}
+
+	check.assignment(x, lhs.typ, context)
+	if x.mode == invalid {
+		return nil
+	}
+
+	return x.typ
+}
+
+func (check *Checker) assignVar(lhs ast.Expr, x *operand) Type {
+	if x.mode == invalid || x.typ == Typ[Invalid] {
+		return nil
+	}
+
+	// Determine if the lhs is a (possibly parenthesized) identifier.
+	ident, _ := unparen(lhs).(*ast.Ident)
+
+	// Don't evaluate lhs if it is the blank identifier.
+	if ident != nil && ident.Name == "_" {
+		check.recordDef(ident, nil)
+		check.assignment(x, nil, "assignment to _ identifier")
+		if x.mode == invalid {
+			return nil
+		}
+		return x.typ
+	}
+
+	// If the lhs is an identifier denoting a variable v, this assignment
+	// is not a 'use' of v. Remember current value of v.used and restore
+	// after evaluating the lhs via check.expr.
+	var v *Var
+	var v_used bool
+	if ident != nil {
+		if _, obj := check.scope.LookupParent(ident.Name, token.NoPos); obj != nil {
+			// It's ok to mark non-local variables, but ignore variables
+			// from other packages to avoid potential race conditions with
+			// dot-imported variables.
+			if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
+				v = w
+				v_used = v.used
+			}
+		}
+	}
+
+	var z operand
+	check.expr(&z, lhs)
+	if v != nil {
+		v.used = v_used // restore v.used
+	}
+
+	if z.mode == invalid || z.typ == Typ[Invalid] {
+		return nil
+	}
+
+	// spec: "Each left-hand side operand must be addressable, a map index
+	// expression, or the blank identifier. Operands may be parenthesized."
+	switch z.mode {
+	case invalid:
+		return nil
+	case variable, mapindex:
+		// ok
+	default:
+		if sel, ok := z.expr.(*ast.SelectorExpr); ok {
+			var op operand
+			check.expr(&op, sel.X)
+			if op.mode == mapindex {
+				check.errorf(z.pos(), "cannot assign to struct field %s in map", ExprString(z.expr))
+				return nil
+			}
+		}
+		check.errorf(z.pos(), "cannot assign to %s", &z)
+		return nil
+	}
+
+	check.assignment(x, z.typ, "assignment")
+	if x.mode == invalid {
+		return nil
+	}
+
+	return x.typ
+}
+
+// If returnPos is valid, initVars is called to type-check the assignment of
+// return expressions, and returnPos is the position of the return statement.
+func (check *Checker) initVars(lhs []*Var, rhs []ast.Expr, returnPos token.Pos) {
+	l := len(lhs)
+	get, r, commaOk := unpack(func(x *operand, i int) { check.multiExpr(x, rhs[i]) }, len(rhs), l == 2 && !returnPos.IsValid())
+	if get == nil || l != r {
+		// invalidate lhs and use rhs
+		for _, obj := range lhs {
+			if obj.typ == nil {
+				obj.typ = Typ[Invalid]
+			}
+		}
+		if get == nil {
+			return // error reported by unpack
+		}
+		check.useGetter(get, r)
+		if returnPos.IsValid() {
+			check.errorf(returnPos, "wrong number of return values (want %d, got %d)", l, r)
+			return
+		}
+		check.errorf(rhs[0].Pos(), "cannot initialize %d variables with %d values", l, r)
+		return
+	}
+
+	context := "assignment"
+	if returnPos.IsValid() {
+		context = "return statement"
+	}
+
+	var x operand
+	if commaOk {
+		var a [2]Type
+		for i := range a {
+			get(&x, i)
+			a[i] = check.initVar(lhs[i], &x, context)
+		}
+		check.recordCommaOkTypes(rhs[0], a)
+		return
+	}
+
+	for i, lhs := range lhs {
+		get(&x, i)
+		check.initVar(lhs, &x, context)
+	}
+}
+
+func (check *Checker) assignVars(lhs, rhs []ast.Expr) {
+	l := len(lhs)
+	get, r, commaOk := unpack(func(x *operand, i int) { check.multiExpr(x, rhs[i]) }, len(rhs), l == 2)
+	if get == nil {
+		check.useLHS(lhs...)
+		return // error reported by unpack
+	}
+	if l != r {
+		check.useGetter(get, r)
+		check.errorf(rhs[0].Pos(), "cannot assign %d values to %d variables", r, l)
+		return
+	}
+
+	var x operand
+	if commaOk {
+		var a [2]Type
+		for i := range a {
+			get(&x, i)
+			a[i] = check.assignVar(lhs[i], &x)
+		}
+		check.recordCommaOkTypes(rhs[0], a)
+		return
+	}
+
+	for i, lhs := range lhs {
+		get(&x, i)
+		check.assignVar(lhs, &x)
+	}
+}
+
+func (check *Checker) shortVarDecl(pos token.Pos, lhs, rhs []ast.Expr) {
+	scope := check.scope
+
+	// collect lhs variables
+	var newVars []*Var
+	var lhsVars = make([]*Var, len(lhs))
+	for i, lhs := range lhs {
+		var obj *Var
+		if ident, _ := lhs.(*ast.Ident); ident != nil {
+			// Use the correct obj if the ident is redeclared. The
+			// variable's scope starts after the declaration; so we
+			// must use Scope.Lookup here and call Scope.Insert
+			// (via check.declare) later.
+			name := ident.Name
+			if alt := scope.Lookup(name); alt != nil {
+				// redeclared object must be a variable
+				if alt, _ := alt.(*Var); alt != nil {
+					obj = alt
+				} else {
+					check.errorf(lhs.Pos(), "cannot assign to %s", lhs)
+				}
+				check.recordUse(ident, alt)
+			} else {
+				// declare new variable, possibly a blank (_) variable
+				obj = NewVar(ident.Pos(), check.pkg, name, nil)
+				if name != "_" {
+					newVars = append(newVars, obj)
+				}
+				check.recordDef(ident, obj)
+			}
+		} else {
+			check.errorf(lhs.Pos(), "cannot declare %s", lhs)
+		}
+		if obj == nil {
+			obj = NewVar(lhs.Pos(), check.pkg, "_", nil) // dummy variable
+		}
+		lhsVars[i] = obj
+	}
+
+	check.initVars(lhsVars, rhs, token.NoPos)
+
+	// declare new variables
+	if len(newVars) > 0 {
+		// spec: "The scope of a constant or variable identifier declared inside
+		// a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl
+		// for short variable declarations) and ends at the end of the innermost
+		// containing block."
+		scopePos := rhs[len(rhs)-1].End()
+		for _, obj := range newVars {
+			check.declare(scope, nil, obj, scopePos) // recordObject already called
+		}
+	} else {
+		check.softErrorf(pos, "no new variables on left side of :=")
+	}
+}

third_party/forked/golang/go/types/builtins.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of builtin function calls.
+
+package types
+
+import (
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+// builtin type-checks a call to the built-in specified by id and
+// returns true if the call is valid, with *x holding the result;
+// but x.expr is not set. If the call is invalid, the result is
+// false, and *x is undefined.
+//
+func (check *Checker) builtin(x *operand, call *ast.CallExpr, id builtinId) (_ bool) {
+	// append is the only built-in that permits the use of ... for the last argument
+	bin := predeclaredFuncs[id]
+	if call.Ellipsis.IsValid() && id != _Append {
+		check.invalidOp(call.Ellipsis, "invalid use of ... with built-in %s", bin.name)
+		check.use(call.Args...)
+		return
+	}
+
+	// For len(x) and cap(x) we need to know if x contains any function calls or
+	// receive operations. Save/restore current setting and set hasCallOrRecv to
+	// false for the evaluation of x so that we can check it afterwards.
+	// Note: We must do this _before_ calling unpack because unpack evaluates the
+	//       first argument before we even call arg(x, 0)!
+	if id == _Len || id == _Cap {
+		defer func(b bool) {
+			check.hasCallOrRecv = b
+		}(check.hasCallOrRecv)
+		check.hasCallOrRecv = false
+	}
+
+	// determine actual arguments
+	var arg getter
+	nargs := len(call.Args)
+	switch id {
+	default:
+		// make argument getter
+		arg, nargs, _ = unpack(func(x *operand, i int) { check.multiExpr(x, call.Args[i]) }, nargs, false)
+		if arg == nil {
+			return
+		}
+		// evaluate first argument, if present
+		if nargs > 0 {
+			arg(x, 0)
+			if x.mode == invalid {
+				return
+			}
+		}
+	case _Make, _New, _Offsetof, _Trace:
+		// arguments require special handling
+	}
+
+	// check argument count
+	{
+		msg := ""
+		if nargs < bin.nargs {
+			msg = "not enough"
+		} else if !bin.variadic && nargs > bin.nargs {
+			msg = "too many"
+		}
+		if msg != "" {
+			check.invalidOp(call.Rparen, "%s arguments for %s (expected %d, found %d)", msg, call, bin.nargs, nargs)
+			return
+		}
+	}
+
+	switch id {
+	case _Append:
+		// append(s S, x ...T) S, where T is the element type of S
+		// spec: "The variadic function append appends zero or more values x to s of type
+		// S, which must be a slice type, and returns the resulting slice, also of type S.
+		// The values x are passed to a parameter of type ...T where T is the element type
+		// of S and the respective parameter passing rules apply."
+		S := x.typ
+		var T Type
+		if s, _ := S.Underlying().(*Slice); s != nil {
+			T = s.elem
+		} else {
+			check.invalidArg(x.pos(), "%s is not a slice", x)
+			return
+		}
+
+		// remember arguments that have been evaluated already
+		alist := []operand{*x}
+
+		// spec: "As a special case, append also accepts a first argument assignable
+		// to type []byte with a second argument of string type followed by ... .
+		// This form appends the bytes of the string.
+		if nargs == 2 && call.Ellipsis.IsValid() && x.assignableTo(check.conf, NewSlice(universeByte), nil) {
+			arg(x, 1)
+			if x.mode == invalid {
+				return
+			}
+			if isString(x.typ) {
+				if check.Types != nil {
+					sig := makeSig(S, S, x.typ)
+					sig.variadic = true
+					check.recordBuiltinType(call.Fun, sig)
+				}
+				x.mode = value
+				x.typ = S
+				break
+			}
+			alist = append(alist, *x)
+			// fallthrough
+		}
+
+		// check general case by creating custom signature
+		sig := makeSig(S, S, NewSlice(T)) // []T required for variadic signature
+		sig.variadic = true
+		check.arguments(x, call, sig, func(x *operand, i int) {
+			// only evaluate arguments that have not been evaluated before
+			if i < len(alist) {
+				*x = alist[i]
+				return
+			}
+			arg(x, i)
+		}, nargs)
+		// ok to continue even if check.arguments reported errors
+
+		x.mode = value
+		x.typ = S
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, sig)
+		}
+
+	case _Cap, _Len:
+		// cap(x)
+		// len(x)
+		mode := invalid
+		var typ Type
+		var val constant.Value
+		switch typ = implicitArrayDeref(x.typ.Underlying()); t := typ.(type) {
+		case *Basic:
+			if isString(t) && id == _Len {
+				if x.mode == constant_ {
+					mode = constant_
+					val = constant.MakeInt64(int64(len(constant.StringVal(x.val))))
+				} else {
+					mode = value
+				}
+			}
+
+		case *Array:
+			mode = value
+			// spec: "The expressions len(s) and cap(s) are constants
+			// if the type of s is an array or pointer to an array and
+			// the expression s does not contain channel receives or
+			// function calls; in this case s is not evaluated."
+			if !check.hasCallOrRecv {
+				mode = constant_
+				if t.len >= 0 {
+					val = constant.MakeInt64(t.len)
+				} else {
+					val = constant.MakeUnknown()
+				}
+			}
+
+		case *Slice, *Chan:
+			mode = value
+
+		case *Map:
+			if id == _Len {
+				mode = value
+			}
+		}
+
+		if mode == invalid {
+			check.invalidArg(x.pos(), "%s for %s", x, bin.name)
+			return
+		}
+
+		x.mode = mode
+		x.typ = Typ[Int]
+		x.val = val
+		if check.Types != nil && mode != constant_ {
+			check.recordBuiltinType(call.Fun, makeSig(x.typ, typ))
+		}
+
+	case _Close:
+		// close(c)
+		c, _ := x.typ.Underlying().(*Chan)
+		if c == nil {
+			check.invalidArg(x.pos(), "%s is not a channel", x)
+			return
+		}
+		if c.dir == RecvOnly {
+			check.invalidArg(x.pos(), "%s must not be a receive-only channel", x)
+			return
+		}
+
+		x.mode = novalue
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(nil, c))
+		}
+
+	case _Complex:
+		// complex(x, y floatT) complexT
+		var y operand
+		arg(&y, 1)
+		if y.mode == invalid {
+			return
+		}
+
+		// convert or check untyped arguments
+		d := 0
+		if isUntyped(x.typ) {
+			d |= 1
+		}
+		if isUntyped(y.typ) {
+			d |= 2
+		}
+		switch d {
+		case 0:
+			// x and y are typed => nothing to do
+		case 1:
+			// only x is untyped => convert to type of y
+			check.convertUntyped(x, y.typ)
+		case 2:
+			// only y is untyped => convert to type of x
+			check.convertUntyped(&y, x.typ)
+		case 3:
+			// x and y are untyped =>
+			// 1) if both are constants, convert them to untyped
+			//    floating-point numbers if possible,
+			// 2) if one of them is not constant (possible because
+			//    it contains a shift that is yet untyped), convert
+			//    both of them to float64 since they must have the
+			//    same type to succeed (this will result in an error
+			//    because shifts of floats are not permitted)
+			if x.mode == constant_ && y.mode == constant_ {
+				toFloat := func(x *operand) {
+					if isNumeric(x.typ) && constant.Sign(constant.Imag(x.val)) == 0 {
+						x.typ = Typ[UntypedFloat]
+					}
+				}
+				toFloat(x)
+				toFloat(&y)
+			} else {
+				check.convertUntyped(x, Typ[Float64])
+				check.convertUntyped(&y, Typ[Float64])
+				// x and y should be invalid now, but be conservative
+				// and check below
+			}
+		}
+		if x.mode == invalid || y.mode == invalid {
+			return
+		}
+
+		// both argument types must be identical
+		if !Identical(x.typ, y.typ) {
+			check.invalidArg(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
+			return
+		}
+
+		// the argument types must be of floating-point type
+		if !isFloat(x.typ) {
+			check.invalidArg(x.pos(), "arguments have type %s, expected floating-point", x.typ)
+			return
+		}
+
+		// if both arguments are constants, the result is a constant
+		if x.mode == constant_ && y.mode == constant_ {
+			x.val = constant.BinaryOp(constant.ToFloat(x.val), token.ADD, constant.MakeImag(constant.ToFloat(y.val)))
+		} else {
+			x.mode = value
+		}
+
+		// determine result type
+		var res BasicKind
+		switch x.typ.Underlying().(*Basic).kind {
+		case Float32:
+			res = Complex64
+		case Float64:
+			res = Complex128
+		case UntypedFloat:
+			res = UntypedComplex
+		default:
+			unreachable()
+		}
+		resTyp := Typ[res]
+
+		if check.Types != nil && x.mode != constant_ {
+			check.recordBuiltinType(call.Fun, makeSig(resTyp, x.typ, x.typ))
+		}
+
+		x.typ = resTyp
+
+	case _Copy:
+		// copy(x, y []T) int
+		var dst Type
+		if t, _ := x.typ.Underlying().(*Slice); t != nil {
+			dst = t.elem
+		}
+
+		var y operand
+		arg(&y, 1)
+		if y.mode == invalid {
+			return
+		}
+		var src Type
+		switch t := y.typ.Underlying().(type) {
+		case *Basic:
+			if isString(y.typ) {
+				src = universeByte
+			}
+		case *Slice:
+			src = t.elem
+		}
+
+		if dst == nil || src == nil {
+			check.invalidArg(x.pos(), "copy expects slice arguments; found %s and %s", x, &y)
+			return
+		}
+
+		if !Identical(dst, src) {
+			check.invalidArg(x.pos(), "arguments to copy %s and %s have different element types %s and %s", x, &y, dst, src)
+			return
+		}
+
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(Typ[Int], x.typ, y.typ))
+		}
+		x.mode = value
+		x.typ = Typ[Int]
+
+	case _Delete:
+		// delete(m, k)
+		m, _ := x.typ.Underlying().(*Map)
+		if m == nil {
+			check.invalidArg(x.pos(), "%s is not a map", x)
+			return
+		}
+		arg(x, 1) // k
+		if x.mode == invalid {
+			return
+		}
+
+		if !x.assignableTo(check.conf, m.key, nil) {
+			check.invalidArg(x.pos(), "%s is not assignable to %s", x, m.key)
+			return
+		}
+
+		x.mode = novalue
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(nil, m, m.key))
+		}
+
+	case _Imag, _Real:
+		// imag(complexT) floatT
+		// real(complexT) floatT
+
+		// convert or check untyped argument
+		if isUntyped(x.typ) {
+			if x.mode == constant_ {
+				// an untyped constant number can alway be considered
+				// as a complex constant
+				if isNumeric(x.typ) {
+					x.typ = Typ[UntypedComplex]
+				}
+			} else {
+				// an untyped non-constant argument may appear if
+				// it contains a (yet untyped non-constant) shift
+				// expression: convert it to complex128 which will
+				// result in an error (shift of complex value)
+				check.convertUntyped(x, Typ[Complex128])
+				// x should be invalid now, but be conservative and check
+				if x.mode == invalid {
+					return
+				}
+			}
+		}
+
+		// the argument must be of complex type
+		if !isComplex(x.typ) {
+			check.invalidArg(x.pos(), "argument has type %s, expected complex type", x.typ)
+			return
+		}
+
+		// if the argument is a constant, the result is a constant
+		if x.mode == constant_ {
+			if id == _Real {
+				x.val = constant.Real(x.val)
+			} else {
+				x.val = constant.Imag(x.val)
+			}
+		} else {
+			x.mode = value
+		}
+
+		// determine result type
+		var res BasicKind
+		switch x.typ.Underlying().(*Basic).kind {
+		case Complex64:
+			res = Float32
+		case Complex128:
+			res = Float64
+		case UntypedComplex:
+			res = UntypedFloat
+		default:
+			unreachable()
+		}
+		resTyp := Typ[res]
+
+		if check.Types != nil && x.mode != constant_ {
+			check.recordBuiltinType(call.Fun, makeSig(resTyp, x.typ))
+		}
+
+		x.typ = resTyp
+
+	case _Make:
+		// make(T, n)
+		// make(T, n, m)
+		// (no argument evaluated yet)
+		arg0 := call.Args[0]
+		T := check.typ(arg0)
+		if T == Typ[Invalid] {
+			return
+		}
+
+		var min int // minimum number of arguments
+		switch T.Underlying().(type) {
+		case *Slice:
+			min = 2
+		case *Map, *Chan:
+			min = 1
+		default:
+			check.invalidArg(arg0.Pos(), "cannot make %s; type must be slice, map, or channel", arg0)
+			return
+		}
+		if nargs < min || min+1 < nargs {
+			check.errorf(call.Pos(), "%v expects %d or %d arguments; found %d", call, min, min+1, nargs)
+			return
+		}
+		var sizes []int64 // constant integer arguments, if any
+		for _, arg := range call.Args[1:] {
+			if s, ok := check.index(arg, -1); ok && s >= 0 {
+				sizes = append(sizes, s)
+			}
+		}
+		if len(sizes) == 2 && sizes[0] > sizes[1] {
+			check.invalidArg(call.Args[1].Pos(), "length and capacity swapped")
+			// safe to continue
+		}
+		x.mode = value
+		x.typ = T
+		if check.Types != nil {
+			params := [...]Type{T, Typ[Int], Typ[Int]}
+			check.recordBuiltinType(call.Fun, makeSig(x.typ, params[:1+len(sizes)]...))
+		}
+
+	case _New:
+		// new(T)
+		// (no argument evaluated yet)
+		T := check.typ(call.Args[0])
+		if T == Typ[Invalid] {
+			return
+		}
+
+		x.mode = value
+		x.typ = &Pointer{base: T}
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(x.typ, T))
+		}
+
+	case _Panic:
+		// panic(x)
+		check.assignment(x, &emptyInterface, "argument to panic")
+		if x.mode == invalid {
+			return
+		}
+
+		x.mode = novalue
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(nil, &emptyInterface))
+		}
+
+	case _Print, _Println:
+		// print(x, y, ...)
+		// println(x, y, ...)
+		var params []Type
+		if nargs > 0 {
+			params = make([]Type, nargs)
+			for i := 0; i < nargs; i++ {
+				if i > 0 {
+					arg(x, i) // first argument already evaluated
+				}
+				check.assignment(x, nil, "argument to "+predeclaredFuncs[id].name)
+				if x.mode == invalid {
+					// TODO(gri) "use" all arguments?
+					return
+				}
+				params[i] = x.typ
+			}
+		}
+
+		x.mode = novalue
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(nil, params...))
+		}
+
+	case _Recover:
+		// recover() interface{}
+		x.mode = value
+		x.typ = &emptyInterface
+		if check.Types != nil {
+			check.recordBuiltinType(call.Fun, makeSig(x.typ))
+		}
+
+	case _Alignof:
+		// unsafe.Alignof(x T) uintptr
+		check.assignment(x, nil, "argument to unsafe.Alignof")
+		if x.mode == invalid {
+			return
+		}
+
+		x.mode = constant_
+		x.val = constant.MakeInt64(check.conf.alignof(x.typ))
+		x.typ = Typ[Uintptr]
+		// result is constant - no need to record signature
+
+	case _Offsetof:
+		// unsafe.Offsetof(x T) uintptr, where x must be a selector
+		// (no argument evaluated yet)
+		arg0 := call.Args[0]
+		selx, _ := unparen(arg0).(*ast.SelectorExpr)
+		if selx == nil {
+			check.invalidArg(arg0.Pos(), "%s is not a selector expression", arg0)
+			check.use(arg0)
+			return
+		}
+
+		check.expr(x, selx.X)
+		if x.mode == invalid {
+			return
+		}
+
+		base := derefStructPtr(x.typ)
+		sel := selx.Sel.Name
+		obj, index, indirect := LookupFieldOrMethod(base, false, check.pkg, sel)
+		switch obj.(type) {
+		case nil:
+			check.invalidArg(x.pos(), "%s has no single field %s", base, sel)
+			return
+		case *Func:
+			// TODO(gri) Using derefStructPtr may result in methods being found
+			// that don't actually exist. An error either way, but the error
+			// message is confusing. See: https://play.golang.org/p/al75v23kUy ,
+			// but go/types reports: "invalid argument: x.m is a method value".
+			check.invalidArg(arg0.Pos(), "%s is a method value", arg0)
+			return
+		}
+		if indirect {
+			check.invalidArg(x.pos(), "field %s is embedded via a pointer in %s", sel, base)
+			return
+		}
+
+		// TODO(gri) Should we pass x.typ instead of base (and indirect report if derefStructPtr indirected)?
+		check.recordSelection(selx, FieldVal, base, obj, index, false)
+
+		offs := check.conf.offsetof(base, index)
+		x.mode = constant_
+		x.val = constant.MakeInt64(offs)
+		x.typ = Typ[Uintptr]
+		// result is constant - no need to record signature
+
+	case _Sizeof:
+		// unsafe.Sizeof(x T) uintptr
+		check.assignment(x, nil, "argument to unsafe.Sizeof")
+		if x.mode == invalid {
+			return
+		}
+
+		x.mode = constant_
+		x.val = constant.MakeInt64(check.conf.sizeof(x.typ))
+		x.typ = Typ[Uintptr]
+		// result is constant - no need to record signature
+
+	case _Assert:
+		// assert(pred) causes a typechecker error if pred is false.
+		// The result of assert is the value of pred if there is no error.
+		// Note: assert is only available in self-test mode.
+		if x.mode != constant_ || !isBoolean(x.typ) {
+			check.invalidArg(x.pos(), "%s is not a boolean constant", x)
+			return
+		}
+		if x.val.Kind() != constant.Bool {
+			check.errorf(x.pos(), "internal error: value of %s should be a boolean constant", x)
+			return
+		}
+		if !constant.BoolVal(x.val) {
+			check.errorf(call.Pos(), "%v failed", call)
+			// compile-time assertion failure - safe to continue
+		}
+		// result is constant - no need to record signature
+
+	case _Trace:
+		// trace(x, y, z, ...) dumps the positions, expressions, and
+		// values of its arguments. The result of trace is the value
+		// of the first argument.
+		// Note: trace is only available in self-test mode.
+		// (no argument evaluated yet)
+		if nargs == 0 {
+			check.dump("%s: trace() without arguments", call.Pos())
+			x.mode = novalue
+			break
+		}
+		var t operand
+		x1 := x
+		for _, arg := range call.Args {
+			check.rawExpr(x1, arg, nil) // permit trace for types, e.g.: new(trace(T))
+			check.dump("%s: %s", x1.pos(), x1)
+			x1 = &t // use incoming x only for first argument
+		}
+		// trace is only available in test mode - no need to record signature
+
+	default:
+		unreachable()
+	}
+
+	return true
+}
+
+// makeSig makes a signature for the given argument and result types.
+// Default types are used for untyped arguments, and res may be nil.
+func makeSig(res Type, args ...Type) *Signature {
+	list := make([]*Var, len(args))
+	for i, param := range args {
+		list[i] = NewVar(token.NoPos, nil, "", Default(param))
+	}
+	params := NewTuple(list...)
+	var result *Tuple
+	if res != nil {
+		assert(!isUntyped(res))
+		result = NewTuple(NewVar(token.NoPos, nil, "", res))
+	}
+	return &Signature{params: params, results: result}
+}
+
+// implicitArrayDeref returns A if typ is of the form *A and A is an array;
+// otherwise it returns typ.
+//
+func implicitArrayDeref(typ Type) Type {
+	if p, ok := typ.(*Pointer); ok {
+		if a, ok := p.base.Underlying().(*Array); ok {
+			return a
+		}
+	}
+	return typ
+}
+
+// unparen returns e with any enclosing parentheses stripped.
+func unparen(e ast.Expr) ast.Expr {
+	for {
+		p, ok := e.(*ast.ParenExpr)
+		if !ok {
+			return e
+		}
+		e = p.X
+	}
+}

third_party/forked/golang/go/types/call.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of call and selector expressions.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+func (check *Checker) call(x *operand, e *ast.CallExpr) exprKind {
+	check.exprOrType(x, e.Fun)
+
+	switch x.mode {
+	case invalid:
+		check.use(e.Args...)
+		x.mode = invalid
+		x.expr = e
+		return statement
+
+	case typexpr:
+		// conversion
+		T := x.typ
+		x.mode = invalid
+		switch n := len(e.Args); n {
+		case 0:
+			check.errorf(e.Rparen, "missing argument in conversion to %s", T)
+		case 1:
+			check.expr(x, e.Args[0])
+			if x.mode != invalid {
+				check.conversion(x, T)
+			}
+		default:
+			check.errorf(e.Args[n-1].Pos(), "too many arguments in conversion to %s", T)
+		}
+		x.expr = e
+		return conversion
+
+	case builtin:
+		id := x.id
+		if !check.builtin(x, e, id) {
+			x.mode = invalid
+		}
+		x.expr = e
+		// a non-constant result implies a function call
+		if x.mode != invalid && x.mode != constant_ {
+			check.hasCallOrRecv = true
+		}
+		return predeclaredFuncs[id].kind
+
+	default:
+		// function/method call
+		sig, _ := x.typ.Underlying().(*Signature)
+		if sig == nil {
+			check.invalidOp(x.pos(), "cannot call non-function %s", x)
+			x.mode = invalid
+			x.expr = e
+			return statement
+		}
+
+		arg, n, _ := unpack(func(x *operand, i int) { check.multiExpr(x, e.Args[i]) }, len(e.Args), false)
+		if arg != nil {
+			check.arguments(x, e, sig, arg, n)
+		} else {
+			x.mode = invalid
+		}
+
+		// determine result
+		switch sig.results.Len() {
+		case 0:
+			x.mode = novalue
+		case 1:
+			x.mode = value
+			x.typ = sig.results.vars[0].typ // unpack tuple
+		default:
+			x.mode = value
+			x.typ = sig.results
+		}
+
+		x.expr = e
+		check.hasCallOrRecv = true
+
+		return statement
+	}
+}
+
+// use type-checks each argument.
+// Useful to make sure expressions are evaluated
+// (and variables are "used") in the presence of other errors.
+// The arguments may be nil.
+func (check *Checker) use(arg ...ast.Expr) {
+	var x operand
+	for _, e := range arg {
+		// The nil check below is necessary since certain AST fields
+		// may legally be nil (e.g., the ast.SliceExpr.High field).
+		if e != nil {
+			check.rawExpr(&x, e, nil)
+		}
+	}
+}
+
+// useLHS is like use, but doesn't "use" top-level identifiers.
+// It should be called instead of use if the arguments are
+// expressions on the lhs of an assignment.
+// The arguments must not be nil.
+func (check *Checker) useLHS(arg ...ast.Expr) {
+	var x operand
+	for _, e := range arg {
+		// If the lhs is an identifier denoting a variable v, this assignment
+		// is not a 'use' of v. Remember current value of v.used and restore
+		// after evaluating the lhs via check.rawExpr.
+		var v *Var
+		var v_used bool
+		if ident, _ := unparen(e).(*ast.Ident); ident != nil {
+			// never type-check the blank name on the lhs
+			if ident.Name == "_" {
+				continue
+			}
+			if _, obj := check.scope.LookupParent(ident.Name, token.NoPos); obj != nil {
+				// It's ok to mark non-local variables, but ignore variables
+				// from other packages to avoid potential race conditions with
+				// dot-imported variables.
+				if w, _ := obj.(*Var); w != nil && w.pkg == check.pkg {
+					v = w
+					v_used = v.used
+				}
+			}
+		}
+		check.rawExpr(&x, e, nil)
+		if v != nil {
+			v.used = v_used // restore v.used
+		}
+	}
+}
+
+// useGetter is like use, but takes a getter instead of a list of expressions.
+// It should be called instead of use if a getter is present to avoid repeated
+// evaluation of the first argument (since the getter was likely obtained via
+// unpack, which may have evaluated the first argument already).
+func (check *Checker) useGetter(get getter, n int) {
+	var x operand
+	for i := 0; i < n; i++ {
+		get(&x, i)
+	}
+}
+
+// A getter sets x as the i'th operand, where 0 <= i < n and n is the total
+// number of operands (context-specific, and maintained elsewhere). A getter
+// type-checks the i'th operand; the details of the actual check are getter-
+// specific.
+type getter func(x *operand, i int)
+
+// unpack takes a getter get and a number of operands n. If n == 1, unpack
+// calls the incoming getter for the first operand. If that operand is
+// invalid, unpack returns (nil, 0, false). Otherwise, if that operand is a
+// function call, or a comma-ok expression and allowCommaOk is set, the result
+// is a new getter and operand count providing access to the function results,
+// or comma-ok values, respectively. The third result value reports if it
+// is indeed the comma-ok case. In all other cases, the incoming getter and
+// operand count are returned unchanged, and the third result value is false.
+//
+// In other words, if there's exactly one operand that - after type-checking
+// by calling get - stands for multiple operands, the resulting getter provides
+// access to those operands instead.
+//
+// If the returned getter is called at most once for a given operand index i
+// (including i == 0), that operand is guaranteed to cause only one call of
+// the incoming getter with that i.
+//
+func unpack(get getter, n int, allowCommaOk bool) (getter, int, bool) {
+	if n != 1 {
+		// zero or multiple values
+		return get, n, false
+	}
+	// possibly result of an n-valued function call or comma,ok value
+	var x0 operand
+	get(&x0, 0)
+	if x0.mode == invalid {
+		return nil, 0, false
+	}
+
+	if t, ok := x0.typ.(*Tuple); ok {
+		// result of an n-valued function call
+		return func(x *operand, i int) {
+			x.mode = value
+			x.expr = x0.expr
+			x.typ = t.At(i).typ
+		}, t.Len(), false
+	}
+
+	if x0.mode == mapindex || x0.mode == commaok {
+		// comma-ok value
+		if allowCommaOk {
+			a := [2]Type{x0.typ, Typ[UntypedBool]}
+			return func(x *operand, i int) {
+				x.mode = value
+				x.expr = x0.expr
+				x.typ = a[i]
+			}, 2, true
+		}
+		x0.mode = value
+	}
+
+	// single value
+	return func(x *operand, i int) {
+		if i != 0 {
+			unreachable()
+		}
+		*x = x0
+	}, 1, false
+}
+
+// arguments checks argument passing for the call with the given signature.
+// The arg function provides the operand for the i'th argument.
+func (check *Checker) arguments(x *operand, call *ast.CallExpr, sig *Signature, arg getter, n int) {
+	if call.Ellipsis.IsValid() {
+		// last argument is of the form x...
+		if !sig.variadic {
+			check.errorf(call.Ellipsis, "cannot use ... in call to non-variadic %s", call.Fun)
+			check.useGetter(arg, n)
+			return
+		}
+		if len(call.Args) == 1 && n > 1 {
+			// f()... is not permitted if f() is multi-valued
+			check.errorf(call.Ellipsis, "cannot use ... with %d-valued %s", n, call.Args[0])
+			check.useGetter(arg, n)
+			return
+		}
+	}
+
+	// evaluate arguments
+	for i := 0; i < n; i++ {
+		arg(x, i)
+		if x.mode != invalid {
+			var ellipsis token.Pos
+			if i == n-1 && call.Ellipsis.IsValid() {
+				ellipsis = call.Ellipsis
+			}
+			check.argument(call.Fun, sig, i, x, ellipsis)
+		}
+	}
+
+	// check argument count
+	if sig.variadic {
+		// a variadic function accepts an "empty"
+		// last argument: count one extra
+		n++
+	}
+	if n < sig.params.Len() {
+		check.errorf(call.Rparen, "too few arguments in call to %s", call.Fun)
+		// ok to continue
+	}
+}
+
+// argument checks passing of argument x to the i'th parameter of the given signature.
+// If ellipsis is valid, the argument is followed by ... at that position in the call.
+func (check *Checker) argument(fun ast.Expr, sig *Signature, i int, x *operand, ellipsis token.Pos) {
+	check.singleValue(x)
+	if x.mode == invalid {
+		return
+	}
+
+	n := sig.params.Len()
+
+	// determine parameter type
+	var typ Type
+	switch {
+	case i < n:
+		typ = sig.params.vars[i].typ
+	case sig.variadic:
+		typ = sig.params.vars[n-1].typ
+		if debug {
+			if _, ok := typ.(*Slice); !ok {
+				check.dump("%s: expected unnamed slice type, got %s", sig.params.vars[n-1].Pos(), typ)
+			}
+		}
+	default:
+		check.errorf(x.pos(), "too many arguments")
+		return
+	}
+
+	if ellipsis.IsValid() {
+		// argument is of the form x... and x is single-valued
+		if i != n-1 {
+			check.errorf(ellipsis, "can only use ... with matching parameter")
+			return
+		}
+		if _, ok := x.typ.Underlying().(*Slice); !ok && x.typ != Typ[UntypedNil] { // see issue #18268
+			check.errorf(x.pos(), "cannot use %s as parameter of type %s", x, typ)
+			return
+		}
+	} else if sig.variadic && i >= n-1 {
+		// use the variadic parameter slice's element type
+		typ = typ.(*Slice).elem
+	}
+
+	check.assignment(x, typ, check.sprintf("argument to %s", fun))
+}
+
+func (check *Checker) selector(x *operand, e *ast.SelectorExpr) {
+	// these must be declared before the "goto Error" statements
+	var (
+		obj      Object
+		index    []int
+		indirect bool
+	)
+
+	sel := e.Sel.Name
+	// If the identifier refers to a package, handle everything here
+	// so we don't need a "package" mode for operands: package names
+	// can only appear in qualified identifiers which are mapped to
+	// selector expressions.
+	if ident, ok := e.X.(*ast.Ident); ok {
+		_, obj := check.scope.LookupParent(ident.Name, check.pos)
+		if pname, _ := obj.(*PkgName); pname != nil {
+			assert(pname.pkg == check.pkg)
+			check.recordUse(ident, pname)
+			pname.used = true
+			pkg := pname.imported
+			exp := pkg.scope.Lookup(sel)
+			if exp == nil {
+				if !pkg.fake {
+					check.errorf(e.Pos(), "%s not declared by package %s", sel, pkg.name)
+				}
+				goto Error
+			}
+			if !exp.Exported() {
+				check.errorf(e.Pos(), "%s not exported by package %s", sel, pkg.name)
+				// ok to continue
+			}
+			check.recordUse(e.Sel, exp)
+
+			// Simplified version of the code for *ast.Idents:
+			// - imported objects are always fully initialized
+			switch exp := exp.(type) {
+			case *Const:
+				assert(exp.Val() != nil)
+				x.mode = constant_
+				x.typ = exp.typ
+				x.val = exp.val
+			case *TypeName:
+				x.mode = typexpr
+				x.typ = exp.typ
+			case *Var:
+				x.mode = variable
+				x.typ = exp.typ
+			case *Func:
+				x.mode = value
+				x.typ = exp.typ
+			case *Builtin:
+				x.mode = builtin
+				x.typ = exp.typ
+				x.id = exp.id
+			default:
+				check.dump("unexpected object %v", exp)
+				unreachable()
+			}
+			x.expr = e
+			return
+		}
+	}
+
+	check.exprOrType(x, e.X)
+	if x.mode == invalid {
+		goto Error
+	}
+
+	obj, index, indirect = LookupFieldOrMethod(x.typ, x.mode == variable, check.pkg, sel)
+	if obj == nil {
+		switch {
+		case index != nil:
+			// TODO(gri) should provide actual type where the conflict happens
+			check.invalidOp(e.Pos(), "ambiguous selector %s", sel)
+		case indirect:
+			check.invalidOp(e.Pos(), "%s is not in method set of %s", sel, x.typ)
+		default:
+			check.invalidOp(e.Pos(), "%s has no field or method %s", x, sel)
+		}
+		goto Error
+	}
+
+	if x.mode == typexpr {
+		// method expression
+		m, _ := obj.(*Func)
+		if m == nil {
+			check.invalidOp(e.Pos(), "%s has no method %s", x, sel)
+			goto Error
+		}
+
+		check.recordSelection(e, MethodExpr, x.typ, m, index, indirect)
+
+		// the receiver type becomes the type of the first function
+		// argument of the method expression's function type
+		var params []*Var
+		sig := m.typ.(*Signature)
+		if sig.params != nil {
+			params = sig.params.vars
+		}
+		x.mode = value
+		x.typ = &Signature{
+			params:   NewTuple(append([]*Var{NewVar(token.NoPos, check.pkg, "", x.typ)}, params...)...),
+			results:  sig.results,
+			variadic: sig.variadic,
+		}
+
+		check.addDeclDep(m)
+
+	} else {
+		// regular selector
+		switch obj := obj.(type) {
+		case *Var:
+			check.recordSelection(e, FieldVal, x.typ, obj, index, indirect)
+			if x.mode == variable || indirect {
+				x.mode = variable
+			} else {
+				x.mode = value
+			}
+			x.typ = obj.typ
+
+		case *Func:
+			// TODO(gri) If we needed to take into account the receiver's
+			// addressability, should we report the type &(x.typ) instead?
+			check.recordSelection(e, MethodVal, x.typ, obj, index, indirect)
+
+			if debug {
+				// Verify that LookupFieldOrMethod and MethodSet.Lookup agree.
+				typ := x.typ
+				if x.mode == variable {
+					// If typ is not an (unnamed) pointer or an interface,
+					// use *typ instead, because the method set of *typ
+					// includes the methods of typ.
+					// Variables are addressable, so we can always take their
+					// address.
+					if _, ok := typ.(*Pointer); !ok && !IsInterface(typ) {
+						typ = &Pointer{base: typ}
+					}
+				}
+				// If we created a synthetic pointer type above, we will throw
+				// away the method set computed here after use.
+				// TODO(gri) Method set computation should probably always compute
+				// both, the value and the pointer receiver method set and represent
+				// them in a single structure.
+				// TODO(gri) Consider also using a method set cache for the lifetime
+				// of checker once we rely on MethodSet lookup instead of individual
+				// lookup.
+				mset := NewMethodSet(typ)
+				if m := mset.Lookup(check.pkg, sel); m == nil || m.obj != obj {
+					check.dump("%s: (%s).%v -> %s", e.Pos(), typ, obj.name, m)
+					check.dump("%s\n", mset)
+					panic("method sets and lookup don't agree")
+				}
+			}
+
+			x.mode = value
+
+			// remove receiver
+			sig := *obj.typ.(*Signature)
+			sig.recv = nil
+			x.typ = &sig
+
+			check.addDeclDep(obj)
+
+		default:
+			unreachable()
+		}
+	}
+
+	// everything went well
+	x.expr = e
+	return
+
+Error:
+	x.mode = invalid
+	x.expr = e
+}

third_party/forked/golang/go/types/check.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements the Check function, which drives type-checking.
+
+package types
+
+import (
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+// debugging/development support
+const (
+	debug = false // leave on during development
+	trace = false // turn on for detailed type resolution traces
+)
+
+// If Strict is set, the type-checker enforces additional
+// rules not specified by the Go 1 spec, but which will
+// catch guaranteed run-time errors if the respective
+// code is executed. In other words, programs passing in
+// Strict mode are Go 1 compliant, but not all Go 1 programs
+// will pass in Strict mode. The additional rules are:
+//
+// - A type assertion x.(T) where T is an interface type
+//   is invalid if any (statically known) method that exists
+//   for both x and T have different signatures.
+//
+const strict = false
+
+// exprInfo stores information about an untyped expression.
+type exprInfo struct {
+	isLhs bool // expression is lhs operand of a shift with delayed type-check
+	mode  operandMode
+	typ   *Basic
+	val   constant.Value // constant value; or nil (if not a constant)
+}
+
+// funcInfo stores the information required for type-checking a function.
+type funcInfo struct {
+	name string    // for debugging/tracing only
+	decl *declInfo // for cycle detection
+	sig  *Signature
+	body *ast.BlockStmt
+}
+
+// A context represents the context within which an object is type-checked.
+type context struct {
+	decl          *declInfo      // package-level declaration whose init expression/function body is checked
+	scope         *Scope         // top-most scope for lookups
+	iota          constant.Value // value of iota in a constant declaration; nil otherwise
+	sig           *Signature     // function signature if inside a function; nil otherwise
+	hasLabel      bool           // set if a function makes use of labels (only ~1% of functions); unused outside functions
+	hasCallOrRecv bool           // set if an expression contains a function call or channel receive operation
+}
+
+// An importKey identifies an imported package by import path and source directory
+// (directory containing the file containing the import). In practice, the directory
+// may always be the same, or may not matter. Given an (import path, directory), an
+// importer must always return the same package (but given two different import paths,
+// an importer may still return the same package by mapping them to the same package
+// paths).
+type importKey struct {
+	path, dir string
+}
+
+// A Checker maintains the state of the type checker.
+// It must be created with NewChecker.
+type Checker struct {
+	// package information
+	// (initialized by NewChecker, valid for the life-time of checker)
+	conf *Config
+	fset *token.FileSet
+	pkg  *Package
+	*Info
+	objMap map[Object]*declInfo   // maps package-level object to declaration info
+	impMap map[importKey]*Package // maps (import path, source directory) to (complete or fake) package
+
+	// information collected during type-checking of a set of package files
+	// (initialized by Files, valid only for the duration of check.Files;
+	// maps and lists are allocated on demand)
+	files            []*ast.File                       // package files
+	unusedDotImports map[*Scope]map[*Package]token.Pos // positions of unused dot-imported packages for each file scope
+
+	firstErr error                 // first error encountered
+	methods  map[string][]*Func    // maps type names to associated methods
+	untyped  map[ast.Expr]exprInfo // map of expressions without final type
+	funcs    []funcInfo            // list of functions to type-check
+	delayed  []func()              // delayed checks requiring fully setup types
+
+	// context within which the current object is type-checked
+	// (valid only for the duration of type-checking a specific object)
+	context
+	pos token.Pos // if valid, identifiers are looked up as if at position pos (used by Eval)
+
+	// debugging
+	indent int // indentation for tracing
+}
+
+// addUnusedImport adds the position of a dot-imported package
+// pkg to the map of dot imports for the given file scope.
+func (check *Checker) addUnusedDotImport(scope *Scope, pkg *Package, pos token.Pos) {
+	mm := check.unusedDotImports
+	if mm == nil {
+		mm = make(map[*Scope]map[*Package]token.Pos)
+		check.unusedDotImports = mm
+	}
+	m := mm[scope]
+	if m == nil {
+		m = make(map[*Package]token.Pos)
+		mm[scope] = m
+	}
+	m[pkg] = pos
+}
+
+// addDeclDep adds the dependency edge (check.decl -> to) if check.decl exists
+func (check *Checker) addDeclDep(to Object) {
+	from := check.decl
+	if from == nil {
+		return // not in a package-level init expression
+	}
+	if _, found := check.objMap[to]; !found {
+		return // to is not a package-level object
+	}
+	from.addDep(to)
+}
+
+func (check *Checker) assocMethod(tname string, meth *Func) {
+	m := check.methods
+	if m == nil {
+		m = make(map[string][]*Func)
+		check.methods = m
+	}
+	m[tname] = append(m[tname], meth)
+}
+
+func (check *Checker) rememberUntyped(e ast.Expr, lhs bool, mode operandMode, typ *Basic, val constant.Value) {
+	m := check.untyped
+	if m == nil {
+		m = make(map[ast.Expr]exprInfo)
+		check.untyped = m
+	}
+	m[e] = exprInfo{lhs, mode, typ, val}
+}
+
+func (check *Checker) later(name string, decl *declInfo, sig *Signature, body *ast.BlockStmt) {
+	check.funcs = append(check.funcs, funcInfo{name, decl, sig, body})
+}
+
+func (check *Checker) delay(f func()) {
+	check.delayed = append(check.delayed, f)
+}
+
+// NewChecker returns a new Checker instance for a given package.
+// Package files may be added incrementally via checker.Files.
+func NewChecker(conf *Config, fset *token.FileSet, pkg *Package, info *Info) *Checker {
+	// make sure we have a configuration
+	if conf == nil {
+		conf = new(Config)
+	}
+
+	// make sure we have an info struct
+	if info == nil {
+		info = new(Info)
+	}
+
+	return &Checker{
+		conf:   conf,
+		fset:   fset,
+		pkg:    pkg,
+		Info:   info,
+		objMap: make(map[Object]*declInfo),
+		impMap: make(map[importKey]*Package),
+	}
+}
+
+// initFiles initializes the files-specific portion of checker.
+// The provided files must all belong to the same package.
+func (check *Checker) initFiles(files []*ast.File) {
+	// start with a clean slate (check.Files may be called multiple times)
+	check.files = nil
+	check.unusedDotImports = nil
+
+	check.firstErr = nil
+	check.methods = nil
+	check.untyped = nil
+	check.funcs = nil
+	check.delayed = nil
+
+	// determine package name and collect valid files
+	pkg := check.pkg
+	for _, file := range files {
+		switch name := file.Name.Name; pkg.name {
+		case "":
+			if name != "_" {
+				pkg.name = name
+			} else {
+				check.errorf(file.Name.Pos(), "invalid package name _")
+			}
+			fallthrough
+
+		case name:
+			check.files = append(check.files, file)
+
+		default:
+			check.errorf(file.Package, "package %s; expected %s", name, pkg.name)
+			// ignore this file
+		}
+	}
+}
+
+// A bailout panic is used for early termination.
+type bailout struct{}
+
+func (check *Checker) handleBailout(err *error) {
+	switch p := recover().(type) {
+	case nil, bailout:
+		// normal return or early exit
+		*err = check.firstErr
+	default:
+		// re-panic
+		panic(p)
+	}
+}
+
+// Files checks the provided files as part of the checker's package.
+func (check *Checker) Files(files []*ast.File) error { return check.checkFiles(files) }
+
+func (check *Checker) checkFiles(files []*ast.File) (err error) {
+	defer check.handleBailout(&err)
+
+	check.initFiles(files)
+
+	check.collectObjects()
+
+	check.packageObjects(check.resolveOrder())
+
+	check.functionBodies()
+
+	check.initOrder()
+
+	if !check.conf.DisableUnusedImportCheck {
+		check.unusedImports()
+	}
+
+	// perform delayed checks
+	for _, f := range check.delayed {
+		f()
+	}
+
+	check.recordUntyped()
+
+	check.pkg.complete = true
+	return
+}
+
+func (check *Checker) recordUntyped() {
+	if !debug && check.Types == nil {
+		return // nothing to do
+	}
+
+	for x, info := range check.untyped {
+		if debug && isTyped(info.typ) {
+			check.dump("%s: %s (type %s) is typed", x.Pos(), x, info.typ)
+			unreachable()
+		}
+		check.recordTypeAndValue(x, info.mode, info.typ, info.val)
+	}
+}
+
+func (check *Checker) recordTypeAndValue(x ast.Expr, mode operandMode, typ Type, val constant.Value) {
+	assert(x != nil)
+	assert(typ != nil)
+	if mode == invalid {
+		return // omit
+	}
+	assert(typ != nil)
+	if mode == constant_ {
+		assert(val != nil)
+		assert(typ == Typ[Invalid] || isConstType(typ))
+	}
+	if m := check.Types; m != nil {
+		m[x] = TypeAndValue{mode, typ, val}
+	}
+}
+
+func (check *Checker) recordBuiltinType(f ast.Expr, sig *Signature) {
+	// f must be a (possibly parenthesized) identifier denoting a built-in
+	// (built-ins in package unsafe always produce a constant result and
+	// we don't record their signatures, so we don't see qualified idents
+	// here): record the signature for f and possible children.
+	for {
+		check.recordTypeAndValue(f, builtin, sig, nil)
+		switch p := f.(type) {
+		case *ast.Ident:
+			return // we're done
+		case *ast.ParenExpr:
+			f = p.X
+		default:
+			unreachable()
+		}
+	}
+}
+
+func (check *Checker) recordCommaOkTypes(x ast.Expr, a [2]Type) {
+	assert(x != nil)
+	if a[0] == nil || a[1] == nil {
+		return
+	}
+	assert(isTyped(a[0]) && isTyped(a[1]) && isBoolean(a[1]))
+	if m := check.Types; m != nil {
+		for {
+			tv := m[x]
+			assert(tv.Type != nil) // should have been recorded already
+			pos := x.Pos()
+			tv.Type = NewTuple(
+				NewVar(pos, check.pkg, "", a[0]),
+				NewVar(pos, check.pkg, "", a[1]),
+			)
+			m[x] = tv
+			// if x is a parenthesized expression (p.X), update p.X
+			p, _ := x.(*ast.ParenExpr)
+			if p == nil {
+				break
+			}
+			x = p.X
+		}
+	}
+}
+
+func (check *Checker) recordDef(id *ast.Ident, obj Object) {
+	assert(id != nil)
+	if m := check.Defs; m != nil {
+		m[id] = obj
+	}
+}
+
+func (check *Checker) recordUse(id *ast.Ident, obj Object) {
+	assert(id != nil)
+	assert(obj != nil)
+	if m := check.Uses; m != nil {
+		m[id] = obj
+	}
+}
+
+func (check *Checker) recordImplicit(node ast.Node, obj Object) {
+	assert(node != nil)
+	assert(obj != nil)
+	if m := check.Implicits; m != nil {
+		m[node] = obj
+	}
+}
+
+func (check *Checker) recordSelection(x *ast.SelectorExpr, kind SelectionKind, recv Type, obj Object, index []int, indirect bool) {
+	assert(obj != nil && (recv == nil || len(index) > 0))
+	check.recordUse(x.Sel, obj)
+	if m := check.Selections; m != nil {
+		m[x] = &Selection{kind, recv, obj, index, indirect}
+	}
+}
+
+func (check *Checker) recordScope(node ast.Node, scope *Scope) {
+	assert(node != nil)
+	assert(scope != nil)
+	if m := check.Scopes; m != nil {
+		m[node] = scope
+	}
+}

third_party/forked/golang/go/types/conversions.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of conversions.
+
+package types
+
+import "go/constant"
+
+// Conversion type-checks the conversion T(x).
+// The result is in x.
+func (check *Checker) conversion(x *operand, T Type) {
+	constArg := x.mode == constant_
+
+	var ok bool
+	switch {
+	case constArg && isConstType(T):
+		// constant conversion
+		switch t := T.Underlying().(*Basic); {
+		case representableConst(x.val, check.conf, t, &x.val):
+			ok = true
+		case isInteger(x.typ) && isString(t):
+			codepoint := int64(-1)
+			if i, ok := constant.Int64Val(x.val); ok {
+				codepoint = i
+			}
+			// If codepoint < 0 the absolute value is too large (or unknown) for
+			// conversion. This is the same as converting any other out-of-range
+			// value - let string(codepoint) do the work.
+			x.val = constant.MakeString(string(codepoint))
+			ok = true
+		}
+	case x.convertibleTo(check.conf, T):
+		// non-constant conversion
+		x.mode = value
+		ok = true
+	}
+
+	if !ok {
+		check.errorf(x.pos(), "cannot convert %s to %s", x, T)
+		x.mode = invalid
+		return
+	}
+
+	// The conversion argument types are final. For untyped values the
+	// conversion provides the type, per the spec: "A constant may be
+	// given a type explicitly by a constant declaration or conversion,...".
+	if isUntyped(x.typ) {
+		final := T
+		// - For conversions to interfaces, use the argument's default type.
+		// - For conversions of untyped constants to non-constant types, also
+		//   use the default type (e.g., []byte("foo") should report string
+		//   not []byte as type for the constant "foo").
+		// - Keep untyped nil for untyped nil arguments.
+		// - For integer to string conversions, keep the argument type.
+		//   (See also the TODO below.)
+		if IsInterface(T) || constArg && !isConstType(T) {
+			final = Default(x.typ)
+		} else if isInteger(x.typ) && isString(T) {
+			final = x.typ
+		}
+		check.updateExprType(x.expr, final, true)
+	}
+
+	x.typ = T
+}
+
+// TODO(gri) convertibleTo checks if T(x) is valid. It assumes that the type
+// of x is fully known, but that's not the case for say string(1<<s + 1.0):
+// Here, the type of 1<<s + 1.0 will be UntypedFloat which will lead to the
+// (correct!) refusal of the conversion. But the reported error is essentially
+// "cannot convert untyped float value to string", yet the correct error (per
+// the spec) is that we cannot shift a floating-point value: 1 in 1<<s should
+// be converted to UntypedFloat because of the addition of 1.0. Fixing this
+// is tricky because we'd have to run updateExprType on the argument first.
+// (Issue #21982.)
+
+func (x *operand) convertibleTo(conf *Config, T Type) bool {
+	// "x is assignable to T"
+	if x.assignableTo(conf, T, nil) {
+		return true
+	}
+
+	// "x's type and T have identical underlying types if tags are ignored"
+	V := x.typ
+	Vu := V.Underlying()
+	Tu := T.Underlying()
+	if IdenticalIgnoreTags(Vu, Tu) {
+		return true
+	}
+
+	// "x's type and T are unnamed pointer types and their pointer base types
+	// have identical underlying types if tags are ignored"
+	if V, ok := V.(*Pointer); ok {
+		if T, ok := T.(*Pointer); ok {
+			if IdenticalIgnoreTags(V.base.Underlying(), T.base.Underlying()) {
+				return true
+			}
+		}
+	}
+
+	// "x's type and T are both integer or floating point types"
+	if (isInteger(V) || isFloat(V)) && (isInteger(T) || isFloat(T)) {
+		return true
+	}
+
+	// "x's type and T are both complex types"
+	if isComplex(V) && isComplex(T) {
+		return true
+	}
+
+	// "x is an integer or a slice of bytes or runes and T is a string type"
+	if (isInteger(V) || isBytesOrRunes(Vu)) && isString(T) {
+		return true
+	}
+
+	// "x is a string and T is a slice of bytes or runes"
+	if isString(V) && isBytesOrRunes(Tu) {
+		return true
+	}
+
+	// package unsafe:
+	// "any pointer or value of underlying type uintptr can be converted into a unsafe.Pointer"
+	if (isPointer(Vu) || isUintptr(Vu)) && isUnsafePointer(T) {
+		return true
+	}
+	// "and vice versa"
+	if isUnsafePointer(V) && (isPointer(Tu) || isUintptr(Tu)) {
+		return true
+	}
+
+	return false
+}
+
+func isUintptr(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.kind == Uintptr
+}
+
+func isUnsafePointer(typ Type) bool {
+	// TODO(gri): Is this (typ.Underlying() instead of just typ) correct?
+	//            The spec does not say so, but gc claims it is. See also
+	//            issue 6326.
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.kind == UnsafePointer
+}
+
+func isPointer(typ Type) bool {
+	_, ok := typ.Underlying().(*Pointer)
+	return ok
+}
+
+func isBytesOrRunes(typ Type) bool {
+	if s, ok := typ.(*Slice); ok {
+		t, ok := s.elem.Underlying().(*Basic)
+		return ok && (t.kind == Byte || t.kind == Rune)
+	}
+	return false
+}

third_party/forked/golang/go/types/decl.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+func (check *Checker) reportAltDecl(obj Object) {
+	if pos := obj.Pos(); pos.IsValid() {
+		// We use "other" rather than "previous" here because
+		// the first declaration seen may not be textually
+		// earlier in the source.
+		check.errorf(pos, "\tother declaration of %s", obj.Name()) // secondary error, \t indented
+	}
+}
+
+func (check *Checker) declare(scope *Scope, id *ast.Ident, obj Object, pos token.Pos) {
+	// spec: "The blank identifier, represented by the underscore
+	// character _, may be used in a declaration like any other
+	// identifier but the declaration does not introduce a new
+	// binding."
+	if obj.Name() != "_" {
+		if alt := scope.Insert(obj); alt != nil {
+			check.errorf(obj.Pos(), "%s redeclared in this block", obj.Name())
+			check.reportAltDecl(alt)
+			return
+		}
+		obj.setScopePos(pos)
+	}
+	if id != nil {
+		check.recordDef(id, obj)
+	}
+}
+
+// objDecl type-checks the declaration of obj in its respective (file) context.
+// See check.typ for the details on def and path.
+func (check *Checker) objDecl(obj Object, def *Named, path []*TypeName) {
+	if obj.Type() != nil {
+		return // already checked - nothing to do
+	}
+
+	if trace {
+		check.trace(obj.Pos(), "-- declaring %s", obj.Name())
+		check.indent++
+		defer func() {
+			check.indent--
+			check.trace(obj.Pos(), "=> %s", obj)
+		}()
+	}
+
+	d := check.objMap[obj]
+	if d == nil {
+		check.dump("%s: %s should have been declared", obj.Pos(), obj.Name())
+		unreachable()
+	}
+
+	// save/restore current context and setup object context
+	defer func(ctxt context) {
+		check.context = ctxt
+	}(check.context)
+	check.context = context{
+		scope: d.file,
+	}
+
+	// Const and var declarations must not have initialization
+	// cycles. We track them by remembering the current declaration
+	// in check.decl. Initialization expressions depending on other
+	// consts, vars, or functions, add dependencies to the current
+	// check.decl.
+	switch obj := obj.(type) {
+	case *Const:
+		check.decl = d // new package-level const decl
+		check.constDecl(obj, d.typ, d.init)
+	case *Var:
+		check.decl = d // new package-level var decl
+		check.varDecl(obj, d.lhs, d.typ, d.init)
+	case *TypeName:
+		// invalid recursive types are detected via path
+		check.typeDecl(obj, d.typ, def, path, d.alias)
+	case *Func:
+		// functions may be recursive - no need to track dependencies
+		check.funcDecl(obj, d)
+	default:
+		unreachable()
+	}
+}
+
+func (check *Checker) constDecl(obj *Const, typ, init ast.Expr) {
+	assert(obj.typ == nil)
+
+	if obj.visited {
+		obj.typ = Typ[Invalid]
+		return
+	}
+	obj.visited = true
+
+	// use the correct value of iota
+	assert(check.iota == nil)
+	check.iota = obj.val
+	defer func() { check.iota = nil }()
+
+	// provide valid constant value under all circumstances
+	obj.val = constant.MakeUnknown()
+
+	// determine type, if any
+	if typ != nil {
+		t := check.typ(typ)
+		if !isConstType(t) {
+			// don't report an error if the type is an invalid C (defined) type
+			// (issue #22090)
+			if t.Underlying() != Typ[Invalid] {
+				check.errorf(typ.Pos(), "invalid constant type %s", t)
+			}
+			obj.typ = Typ[Invalid]
+			return
+		}
+		obj.typ = t
+	}
+
+	// check initialization
+	var x operand
+	if init != nil {
+		check.expr(&x, init)
+	}
+	check.initConst(obj, &x)
+}
+
+func (check *Checker) varDecl(obj *Var, lhs []*Var, typ, init ast.Expr) {
+	assert(obj.typ == nil)
+
+	if obj.visited {
+		obj.typ = Typ[Invalid]
+		return
+	}
+	obj.visited = true
+
+	// var declarations cannot use iota
+	assert(check.iota == nil)
+
+	// determine type, if any
+	if typ != nil {
+		obj.typ = check.typ(typ)
+		// We cannot spread the type to all lhs variables if there
+		// are more than one since that would mark them as checked
+		// (see Checker.objDecl) and the assignment of init exprs,
+		// if any, would not be checked.
+		//
+		// TODO(gri) If we have no init expr, we should distribute
+		// a given type otherwise we need to re-evalate the type
+		// expr for each lhs variable, leading to duplicate work.
+	}
+
+	// check initialization
+	if init == nil {
+		if typ == nil {
+			// error reported before by arityMatch
+			obj.typ = Typ[Invalid]
+		}
+		return
+	}
+
+	if lhs == nil || len(lhs) == 1 {
+		assert(lhs == nil || lhs[0] == obj)
+		var x operand
+		check.expr(&x, init)
+		check.initVar(obj, &x, "variable declaration")
+		return
+	}
+
+	if debug {
+		// obj must be one of lhs
+		found := false
+		for _, lhs := range lhs {
+			if obj == lhs {
+				found = true
+				break
+			}
+		}
+		if !found {
+			panic("inconsistent lhs")
+		}
+	}
+
+	// We have multiple variables on the lhs and one init expr.
+	// Make sure all variables have been given the same type if
+	// one was specified, otherwise they assume the type of the
+	// init expression values (was issue #15755).
+	if typ != nil {
+		for _, lhs := range lhs {
+			lhs.typ = obj.typ
+		}
+	}
+
+	check.initVars(lhs, []ast.Expr{init}, token.NoPos)
+}
+
+// underlying returns the underlying type of typ; possibly by following
+// forward chains of named types. Such chains only exist while named types
+// are incomplete.
+func underlying(typ Type) Type {
+	for {
+		n, _ := typ.(*Named)
+		if n == nil {
+			break
+		}
+		typ = n.underlying
+	}
+	return typ
+}
+
+func (n *Named) setUnderlying(typ Type) {
+	if n != nil {
+		n.underlying = typ
+	}
+}
+
+func (check *Checker) typeDecl(obj *TypeName, typ ast.Expr, def *Named, path []*TypeName, alias bool) {
+	assert(obj.typ == nil)
+
+	// type declarations cannot use iota
+	assert(check.iota == nil)
+
+	if alias {
+
+		obj.typ = Typ[Invalid]
+		obj.typ = check.typExpr(typ, nil, append(path, obj))
+
+	} else {
+
+		named := &Named{obj: obj}
+		def.setUnderlying(named)
+		obj.typ = named // make sure recursive type declarations terminate
+
+		// determine underlying type of named
+		check.typExpr(typ, named, append(path, obj))
+
+		// The underlying type of named may be itself a named type that is
+		// incomplete:
+		//
+		//	type (
+		//		A B
+		//		B *C
+		//		C A
+		//	)
+		//
+		// The type of C is the (named) type of A which is incomplete,
+		// and which has as its underlying type the named type B.
+		// Determine the (final, unnamed) underlying type by resolving
+		// any forward chain (they always end in an unnamed type).
+		named.underlying = underlying(named.underlying)
+
+	}
+
+	// check and add associated methods
+	// TODO(gri) It's easy to create pathological cases where the
+	// current approach is incorrect: In general we need to know
+	// and add all methods _before_ type-checking the type.
+	// See https://play.golang.org/p/WMpE0q2wK8
+	check.addMethodDecls(obj)
+}
+
+func (check *Checker) addMethodDecls(obj *TypeName) {
+	// get associated methods
+	methods := check.methods[obj.name]
+	if len(methods) == 0 {
+		return // no methods
+	}
+	delete(check.methods, obj.name)
+
+	// use an objset to check for name conflicts
+	var mset objset
+
+	// spec: "If the base type is a struct type, the non-blank method
+	// and field names must be distinct."
+	base, _ := obj.typ.(*Named) // nil if receiver base type is type alias
+	if base != nil {
+		if t, _ := base.underlying.(*Struct); t != nil {
+			for _, fld := range t.fields {
+				if fld.name != "_" {
+					assert(mset.insert(fld) == nil)
+				}
+			}
+		}
+
+		// Checker.Files may be called multiple times; additional package files
+		// may add methods to already type-checked types. Add pre-existing methods
+		// so that we can detect redeclarations.
+		for _, m := range base.methods {
+			assert(m.name != "_")
+			assert(mset.insert(m) == nil)
+		}
+	}
+
+	// type-check methods
+	for _, m := range methods {
+		// spec: "For a base type, the non-blank names of methods bound
+		// to it must be unique."
+		if m.name != "_" {
+			if alt := mset.insert(m); alt != nil {
+				switch alt.(type) {
+				case *Var:
+					check.errorf(m.pos, "field and method with the same name %s", m.name)
+				case *Func:
+					check.errorf(m.pos, "method %s already declared for %s", m.name, obj)
+				default:
+					unreachable()
+				}
+				check.reportAltDecl(alt)
+				continue
+			}
+		}
+
+		// type-check
+		check.objDecl(m, nil, nil)
+
+		// methods with blank _ names cannot be found - don't keep them
+		if base != nil && m.name != "_" {
+			base.methods = append(base.methods, m)
+		}
+	}
+}
+
+func (check *Checker) funcDecl(obj *Func, decl *declInfo) {
+	assert(obj.typ == nil)
+
+	// func declarations cannot use iota
+	assert(check.iota == nil)
+
+	sig := new(Signature)
+	obj.typ = sig // guard against cycles
+	fdecl := decl.fdecl
+	check.funcType(sig, fdecl.Recv, fdecl.Type)
+	if sig.recv == nil && obj.name == "init" && (sig.params.Len() > 0 || sig.results.Len() > 0) {
+		check.errorf(fdecl.Pos(), "func init must have no arguments and no return values")
+		// ok to continue
+	}
+
+	// function body must be type-checked after global declarations
+	// (functions implemented elsewhere have no body)
+	if !check.conf.IgnoreFuncBodies && fdecl.Body != nil {
+		check.later(obj.name, decl, sig, fdecl.Body)
+	}
+}
+
+func (check *Checker) declStmt(decl ast.Decl) {
+	pkg := check.pkg
+
+	switch d := decl.(type) {
+	case *ast.BadDecl:
+		// ignore
+
+	case *ast.GenDecl:
+		var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
+		for iota, spec := range d.Specs {
+			switch s := spec.(type) {
+			case *ast.ValueSpec:
+				switch d.Tok {
+				case token.CONST:
+					// determine which init exprs to use
+					switch {
+					case s.Type != nil || len(s.Values) > 0:
+						last = s
+					case last == nil:
+						last = new(ast.ValueSpec) // make sure last exists
+					}
+
+					// declare all constants
+					lhs := make([]*Const, len(s.Names))
+					for i, name := range s.Names {
+						obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(iota)))
+						lhs[i] = obj
+
+						var init ast.Expr
+						if i < len(last.Values) {
+							init = last.Values[i]
+						}
+
+						check.constDecl(obj, last.Type, init)
+					}
+
+					check.arityMatch(s, last)
+
+					// spec: "The scope of a constant or variable identifier declared
+					// inside a function begins at the end of the ConstSpec or VarSpec
+					// (ShortVarDecl for short variable declarations) and ends at the
+					// end of the innermost containing block."
+					scopePos := s.End()
+					for i, name := range s.Names {
+						check.declare(check.scope, name, lhs[i], scopePos)
+					}
+
+				case token.VAR:
+					lhs0 := make([]*Var, len(s.Names))
+					for i, name := range s.Names {
+						lhs0[i] = NewVar(name.Pos(), pkg, name.Name, nil)
+					}
+
+					// initialize all variables
+					for i, obj := range lhs0 {
+						var lhs []*Var
+						var init ast.Expr
+						switch len(s.Values) {
+						case len(s.Names):
+							// lhs and rhs match
+							init = s.Values[i]
+						case 1:
+							// rhs is expected to be a multi-valued expression
+							lhs = lhs0
+							init = s.Values[0]
+						default:
+							if i < len(s.Values) {
+								init = s.Values[i]
+							}
+						}
+						check.varDecl(obj, lhs, s.Type, init)
+						if len(s.Values) == 1 {
+							// If we have a single lhs variable we are done either way.
+							// If we have a single rhs expression, it must be a multi-
+							// valued expression, in which case handling the first lhs
+							// variable will cause all lhs variables to have a type
+							// assigned, and we are done as well.
+							if debug {
+								for _, obj := range lhs0 {
+									assert(obj.typ != nil)
+								}
+							}
+							break
+						}
+					}
+
+					check.arityMatch(s, nil)
+
+					// declare all variables
+					// (only at this point are the variable scopes (parents) set)
+					scopePos := s.End() // see constant declarations
+					for i, name := range s.Names {
+						// see constant declarations
+						check.declare(check.scope, name, lhs0[i], scopePos)
+					}
+
+				default:
+					check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
+				}
+
+			case *ast.TypeSpec:
+				obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Name, nil)
+				// spec: "The scope of a type identifier declared inside a function
+				// begins at the identifier in the TypeSpec and ends at the end of
+				// the innermost containing block."
+				scopePos := s.Name.Pos()
+				check.declare(check.scope, s.Name, obj, scopePos)
+				check.typeDecl(obj, s.Type, nil, nil, s.Assign.IsValid())
+
+			default:
+				check.invalidAST(s.Pos(), "const, type, or var declaration expected")
+			}
+		}
+
+	default:
+		check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
+	}
+}

third_party/forked/golang/go/types/errors.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements various error reporters.
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"strings"
+)
+
+func assert(p bool) {
+	if !p {
+		panic("assertion failed")
+	}
+}
+
+func unreachable() {
+	panic("unreachable")
+}
+
+func (check *Checker) qualifier(pkg *Package) string {
+	if pkg != check.pkg {
+		return pkg.path
+	}
+	return ""
+}
+
+func (check *Checker) sprintf(format string, args ...interface{}) string {
+	for i, arg := range args {
+		switch a := arg.(type) {
+		case nil:
+			arg = "<nil>"
+		case operand:
+			panic("internal error: should always pass *operand")
+		case *operand:
+			arg = operandString(a, check.qualifier)
+		case token.Pos:
+			arg = check.fset.Position(a).String()
+		case ast.Expr:
+			arg = ExprString(a)
+		case Object:
+			arg = ObjectString(a, check.qualifier)
+		case Type:
+			arg = TypeString(a, check.qualifier)
+		}
+		args[i] = arg
+	}
+	return fmt.Sprintf(format, args...)
+}
+
+func (check *Checker) trace(pos token.Pos, format string, args ...interface{}) {
+	fmt.Printf("%s:\t%s%s\n",
+		check.fset.Position(pos),
+		strings.Repeat(".  ", check.indent),
+		check.sprintf(format, args...),
+	)
+}
+
+// dump is only needed for debugging
+func (check *Checker) dump(format string, args ...interface{}) {
+	fmt.Println(check.sprintf(format, args...))
+}
+
+func (check *Checker) err(pos token.Pos, msg string, soft bool) {
+	err := Error{check.fset, pos, msg, soft}
+	if check.firstErr == nil {
+		check.firstErr = err
+	}
+	f := check.conf.Error
+	if f == nil {
+		panic(bailout{}) // report only first error
+	}
+	f(err)
+}
+
+func (check *Checker) error(pos token.Pos, msg string) {
+	check.err(pos, msg, false)
+}
+
+func (check *Checker) errorf(pos token.Pos, format string, args ...interface{}) {
+	check.err(pos, check.sprintf(format, args...), false)
+}
+
+func (check *Checker) softErrorf(pos token.Pos, format string, args ...interface{}) {
+	check.err(pos, check.sprintf(format, args...), true)
+}
+
+func (check *Checker) invalidAST(pos token.Pos, format string, args ...interface{}) {
+	check.errorf(pos, "invalid AST: "+format, args...)
+}
+
+func (check *Checker) invalidArg(pos token.Pos, format string, args ...interface{}) {
+	check.errorf(pos, "invalid argument: "+format, args...)
+}
+
+func (check *Checker) invalidOp(pos token.Pos, format string, args ...interface{}) {
+	check.errorf(pos, "invalid operation: "+format, args...)
+}

third_party/forked/golang/go/types/eval.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"fmt"
+	"go/parser"
+	"go/token"
+)
+
+// Eval returns the type and, if constant, the value for the
+// expression expr, evaluated at position pos of package pkg,
+// which must have been derived from type-checking an AST with
+// complete position information relative to the provided file
+// set.
+//
+// If the expression contains function literals, their bodies
+// are ignored (i.e., the bodies are not type-checked).
+//
+// If pkg == nil, the Universe scope is used and the provided
+// position pos is ignored. If pkg != nil, and pos is invalid,
+// the package scope is used. Otherwise, pos must belong to the
+// package.
+//
+// An error is returned if pos is not within the package or
+// if the node cannot be evaluated.
+//
+// Note: Eval should not be used instead of running Check to compute
+// types and values, but in addition to Check. Eval will re-evaluate
+// its argument each time, and it also does not know about the context
+// in which an expression is used (e.g., an assignment). Thus, top-
+// level untyped constants will return an untyped type rather then the
+// respective context-specific type.
+//
+func Eval(fset *token.FileSet, pkg *Package, pos token.Pos, expr string) (TypeAndValue, error) {
+	// determine scope
+	var scope *Scope
+	if pkg == nil {
+		scope = Universe
+		pos = token.NoPos
+	} else if !pos.IsValid() {
+		scope = pkg.scope
+	} else {
+		// The package scope extent (position information) may be
+		// incorrect (files spread across a wide range of fset
+		// positions) - ignore it and just consider its children
+		// (file scopes).
+		for _, fscope := range pkg.scope.children {
+			if scope = fscope.Innermost(pos); scope != nil {
+				break
+			}
+		}
+		if scope == nil || debug {
+			s := scope
+			for s != nil && s != pkg.scope {
+				s = s.parent
+			}
+			// s == nil || s == pkg.scope
+			if s == nil {
+				return TypeAndValue{}, fmt.Errorf("no position %s found in package %s", fset.Position(pos), pkg.name)
+			}
+		}
+	}
+
+	// parse expressions
+	node, err := parser.ParseExprFrom(fset, "eval", expr, 0)
+	if err != nil {
+		return TypeAndValue{}, err
+	}
+
+	// initialize checker
+	check := NewChecker(nil, fset, pkg, nil)
+	check.scope = scope
+	check.pos = pos
+	defer check.handleBailout(&err)
+
+	// evaluate node
+	var x operand
+	check.rawExpr(&x, node, nil)
+	return TypeAndValue{x.mode, x.typ, x.val}, err
+}

third_party/forked/golang/go/types/expr.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of expressions.
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"math"
+)
+
+/*
+Basic algorithm:
+
+Expressions are checked recursively, top down. Expression checker functions
+are generally of the form:
+
+  func f(x *operand, e *ast.Expr, ...)
+
+where e is the expression to be checked, and x is the result of the check.
+The check performed by f may fail in which case x.mode == invalid, and
+related error messages will have been issued by f.
+
+If a hint argument is present, it is the composite literal element type
+of an outer composite literal; it is used to type-check composite literal
+elements that have no explicit type specification in the source
+(e.g.: []T{{...}, {...}}, the hint is the type T in this case).
+
+All expressions are checked via rawExpr, which dispatches according
+to expression kind. Upon returning, rawExpr is recording the types and
+constant values for all expressions that have an untyped type (those types
+may change on the way up in the expression tree). Usually these are constants,
+but the results of comparisons or non-constant shifts of untyped constants
+may also be untyped, but not constant.
+
+Untyped expressions may eventually become fully typed (i.e., not untyped),
+typically when the value is assigned to a variable, or is used otherwise.
+The updateExprType method is used to record this final type and update
+the recorded types: the type-checked expression tree is again traversed down,
+and the new type is propagated as needed. Untyped constant expression values
+that become fully typed must now be representable by the full type (constant
+sub-expression trees are left alone except for their roots). This mechanism
+ensures that a client sees the actual (run-time) type an untyped value would
+have. It also permits type-checking of lhs shift operands "as if the shift
+were not present": when updateExprType visits an untyped lhs shift operand
+and assigns it it's final type, that type must be an integer type, and a
+constant lhs must be representable as an integer.
+
+When an expression gets its final type, either on the way out from rawExpr,
+on the way down in updateExprType, or at the end of the type checker run,
+the type (and constant value, if any) is recorded via Info.Types, if present.
+*/
+
+type opPredicates map[token.Token]func(Type) bool
+
+var unaryOpPredicates = opPredicates{
+	token.ADD: isNumeric,
+	token.SUB: isNumeric,
+	token.XOR: isInteger,
+	token.NOT: isBoolean,
+}
+
+func (check *Checker) op(m opPredicates, x *operand, op token.Token) bool {
+	if pred := m[op]; pred != nil {
+		if !pred(x.typ) {
+			check.invalidOp(x.pos(), "operator %s not defined for %s", op, x)
+			return false
+		}
+	} else {
+		check.invalidAST(x.pos(), "unknown operator %s", op)
+		return false
+	}
+	return true
+}
+
+// The unary expression e may be nil. It's passed in for better error messages only.
+func (check *Checker) unary(x *operand, e *ast.UnaryExpr, op token.Token) {
+	switch op {
+	case token.AND:
+		// spec: "As an exception to the addressability
+		// requirement x may also be a composite literal."
+		if _, ok := unparen(x.expr).(*ast.CompositeLit); !ok && x.mode != variable {
+			check.invalidOp(x.pos(), "cannot take address of %s", x)
+			x.mode = invalid
+			return
+		}
+		x.mode = value
+		x.typ = &Pointer{base: x.typ}
+		return
+
+	case token.ARROW:
+		typ, ok := x.typ.Underlying().(*Chan)
+		if !ok {
+			check.invalidOp(x.pos(), "cannot receive from non-channel %s", x)
+			x.mode = invalid
+			return
+		}
+		if typ.dir == SendOnly {
+			check.invalidOp(x.pos(), "cannot receive from send-only channel %s", x)
+			x.mode = invalid
+			return
+		}
+		x.mode = commaok
+		x.typ = typ.elem
+		check.hasCallOrRecv = true
+		return
+	}
+
+	if !check.op(unaryOpPredicates, x, op) {
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant_ {
+		typ := x.typ.Underlying().(*Basic)
+		var prec uint
+		if isUnsigned(typ) {
+			prec = uint(check.conf.sizeof(typ) * 8)
+		}
+		x.val = constant.UnaryOp(op, x.val, prec)
+		// Typed constants must be representable in
+		// their type after each constant operation.
+		if isTyped(typ) {
+			if e != nil {
+				x.expr = e // for better error message
+			}
+			check.representable(x, typ)
+		}
+		return
+	}
+
+	x.mode = value
+	// x.typ remains unchanged
+}
+
+func isShift(op token.Token) bool {
+	return op == token.SHL || op == token.SHR
+}
+
+func isComparison(op token.Token) bool {
+	// Note: tokens are not ordered well to make this much easier
+	switch op {
+	case token.EQL, token.NEQ, token.LSS, token.LEQ, token.GTR, token.GEQ:
+		return true
+	}
+	return false
+}
+
+func fitsFloat32(x constant.Value) bool {
+	f32, _ := constant.Float32Val(x)
+	f := float64(f32)
+	return !math.IsInf(f, 0)
+}
+
+func roundFloat32(x constant.Value) constant.Value {
+	f32, _ := constant.Float32Val(x)
+	f := float64(f32)
+	if !math.IsInf(f, 0) {
+		return constant.MakeFloat64(f)
+	}
+	return nil
+}
+
+func fitsFloat64(x constant.Value) bool {
+	f, _ := constant.Float64Val(x)
+	return !math.IsInf(f, 0)
+}
+
+func roundFloat64(x constant.Value) constant.Value {
+	f, _ := constant.Float64Val(x)
+	if !math.IsInf(f, 0) {
+		return constant.MakeFloat64(f)
+	}
+	return nil
+}
+
+// representableConst reports whether x can be represented as
+// value of the given basic type and for the configuration
+// provided (only needed for int/uint sizes).
+//
+// If rounded != nil, *rounded is set to the rounded value of x for
+// representable floating-point and complex values, and to an Int
+// value for integer values; it is left alone otherwise.
+// It is ok to provide the addressof the first argument for rounded.
+func representableConst(x constant.Value, conf *Config, typ *Basic, rounded *constant.Value) bool {
+	if x.Kind() == constant.Unknown {
+		return true // avoid follow-up errors
+	}
+
+	switch {
+	case isInteger(typ):
+		x := constant.ToInt(x)
+		if x.Kind() != constant.Int {
+			return false
+		}
+		if rounded != nil {
+			*rounded = x
+		}
+		if x, ok := constant.Int64Val(x); ok {
+			switch typ.kind {
+			case Int:
+				var s = uint(conf.sizeof(typ)) * 8
+				return int64(-1)<<(s-1) <= x && x <= int64(1)<<(s-1)-1
+			case Int8:
+				const s = 8
+				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
+			case Int16:
+				const s = 16
+				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
+			case Int32:
+				const s = 32
+				return -1<<(s-1) <= x && x <= 1<<(s-1)-1
+			case Int64, UntypedInt:
+				return true
+			case Uint, Uintptr:
+				if s := uint(conf.sizeof(typ)) * 8; s < 64 {
+					return 0 <= x && x <= int64(1)<<s-1
+				}
+				return 0 <= x
+			case Uint8:
+				const s = 8
+				return 0 <= x && x <= 1<<s-1
+			case Uint16:
+				const s = 16
+				return 0 <= x && x <= 1<<s-1
+			case Uint32:
+				const s = 32
+				return 0 <= x && x <= 1<<s-1
+			case Uint64:
+				return 0 <= x
+			default:
+				unreachable()
+			}
+		}
+		// x does not fit into int64
+		switch n := constant.BitLen(x); typ.kind {
+		case Uint, Uintptr:
+			var s = uint(conf.sizeof(typ)) * 8
+			return constant.Sign(x) >= 0 && n <= int(s)
+		case Uint64:
+			return constant.Sign(x) >= 0 && n <= 64
+		case UntypedInt:
+			return true
+		}
+
+	case isFloat(typ):
+		x := constant.ToFloat(x)
+		if x.Kind() != constant.Float {
+			return false
+		}
+		switch typ.kind {
+		case Float32:
+			if rounded == nil {
+				return fitsFloat32(x)
+			}
+			r := roundFloat32(x)
+			if r != nil {
+				*rounded = r
+				return true
+			}
+		case Float64:
+			if rounded == nil {
+				return fitsFloat64(x)
+			}
+			r := roundFloat64(x)
+			if r != nil {
+				*rounded = r
+				return true
+			}
+		case UntypedFloat:
+			return true
+		default:
+			unreachable()
+		}
+
+	case isComplex(typ):
+		x := constant.ToComplex(x)
+		if x.Kind() != constant.Complex {
+			return false
+		}
+		switch typ.kind {
+		case Complex64:
+			if rounded == nil {
+				return fitsFloat32(constant.Real(x)) && fitsFloat32(constant.Imag(x))
+			}
+			re := roundFloat32(constant.Real(x))
+			im := roundFloat32(constant.Imag(x))
+			if re != nil && im != nil {
+				*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+				return true
+			}
+		case Complex128:
+			if rounded == nil {
+				return fitsFloat64(constant.Real(x)) && fitsFloat64(constant.Imag(x))
+			}
+			re := roundFloat64(constant.Real(x))
+			im := roundFloat64(constant.Imag(x))
+			if re != nil && im != nil {
+				*rounded = constant.BinaryOp(re, token.ADD, constant.MakeImag(im))
+				return true
+			}
+		case UntypedComplex:
+			return true
+		default:
+			unreachable()
+		}
+
+	case isString(typ):
+		return x.Kind() == constant.String
+
+	case isBoolean(typ):
+		return x.Kind() == constant.Bool
+	}
+
+	return false
+}
+
+// representable checks that a constant operand is representable in the given basic type.
+func (check *Checker) representable(x *operand, typ *Basic) {
+	assert(x.mode == constant_)
+	if !representableConst(x.val, check.conf, typ, &x.val) {
+		var msg string
+		if isNumeric(x.typ) && isNumeric(typ) {
+			// numeric conversion : error msg
+			//
+			// integer -> integer : overflows
+			// integer -> float   : overflows (actually not possible)
+			// float   -> integer : truncated
+			// float   -> float   : overflows
+			//
+			if !isInteger(x.typ) && isInteger(typ) {
+				msg = "%s truncated to %s"
+			} else {
+				msg = "%s overflows %s"
+			}
+		} else {
+			msg = "cannot convert %s to %s"
+		}
+		check.errorf(x.pos(), msg, x, typ)
+		x.mode = invalid
+	}
+}
+
+// updateExprType updates the type of x to typ and invokes itself
+// recursively for the operands of x, depending on expression kind.
+// If typ is still an untyped and not the final type, updateExprType
+// only updates the recorded untyped type for x and possibly its
+// operands. Otherwise (i.e., typ is not an untyped type anymore,
+// or it is the final type for x), the type and value are recorded.
+// Also, if x is a constant, it must be representable as a value of typ,
+// and if x is the (formerly untyped) lhs operand of a non-constant
+// shift, it must be an integer value.
+//
+func (check *Checker) updateExprType(x ast.Expr, typ Type, final bool) {
+	old, found := check.untyped[x]
+	if !found {
+		return // nothing to do
+	}
+
+	// update operands of x if necessary
+	switch x := x.(type) {
+	case *ast.BadExpr,
+		*ast.FuncLit,
+		*ast.CompositeLit,
+		*ast.IndexExpr,
+		*ast.SliceExpr,
+		*ast.TypeAssertExpr,
+		*ast.StarExpr,
+		*ast.KeyValueExpr,
+		*ast.ArrayType,
+		*ast.StructType,
+		*ast.FuncType,
+		*ast.InterfaceType,
+		*ast.MapType,
+		*ast.ChanType:
+		// These expression are never untyped - nothing to do.
+		// The respective sub-expressions got their final types
+		// upon assignment or use.
+		if debug {
+			check.dump("%s: found old type(%s): %s (new: %s)", x.Pos(), x, old.typ, typ)
+			unreachable()
+		}
+		return
+
+	case *ast.CallExpr:
+		// Resulting in an untyped constant (e.g., built-in complex).
+		// The respective calls take care of calling updateExprType
+		// for the arguments if necessary.
+
+	case *ast.Ident, *ast.BasicLit, *ast.SelectorExpr:
+		// An identifier denoting a constant, a constant literal,
+		// or a qualified identifier (imported untyped constant).
+		// No operands to take care of.
+
+	case *ast.ParenExpr:
+		check.updateExprType(x.X, typ, final)
+
+	case *ast.UnaryExpr:
+		// If x is a constant, the operands were constants.
+		// The operands don't need to be updated since they
+		// never get "materialized" into a typed value. If
+		// left in the untyped map, they will be processed
+		// at the end of the type check.
+		if old.val != nil {
+			break
+		}
+		check.updateExprType(x.X, typ, final)
+
+	case *ast.BinaryExpr:
+		if old.val != nil {
+			break // see comment for unary expressions
+		}
+		if isComparison(x.Op) {
+			// The result type is independent of operand types
+			// and the operand types must have final types.
+		} else if isShift(x.Op) {
+			// The result type depends only on lhs operand.
+			// The rhs type was updated when checking the shift.
+			check.updateExprType(x.X, typ, final)
+		} else {
+			// The operand types match the result type.
+			check.updateExprType(x.X, typ, final)
+			check.updateExprType(x.Y, typ, final)
+		}
+
+	default:
+		unreachable()
+	}
+
+	// If the new type is not final and still untyped, just
+	// update the recorded type.
+	if !final && isUntyped(typ) {
+		old.typ = typ.Underlying().(*Basic)
+		check.untyped[x] = old
+		return
+	}
+
+	// Otherwise we have the final (typed or untyped type).
+	// Remove it from the map of yet untyped expressions.
+	delete(check.untyped, x)
+
+	if old.isLhs {
+		// If x is the lhs of a shift, its final type must be integer.
+		// We already know from the shift check that it is representable
+		// as an integer if it is a constant.
+		if !isInteger(typ) {
+			check.invalidOp(x.Pos(), "shifted operand %s (type %s) must be integer", x, typ)
+			return
+		}
+	} else if old.val != nil {
+		// If x is a constant, it must be representable as a value of typ.
+		c := operand{old.mode, x, old.typ, old.val, 0}
+		check.convertUntyped(&c, typ)
+		if c.mode == invalid {
+			return
+		}
+	}
+
+	// Everything's fine, record final type and value for x.
+	check.recordTypeAndValue(x, old.mode, typ, old.val)
+}
+
+// updateExprVal updates the value of x to val.
+func (check *Checker) updateExprVal(x ast.Expr, val constant.Value) {
+	if info, ok := check.untyped[x]; ok {
+		info.val = val
+		check.untyped[x] = info
+	}
+}
+
+// convertUntyped attempts to set the type of an untyped value to the target type.
+func (check *Checker) convertUntyped(x *operand, target Type) {
+	if x.mode == invalid || isTyped(x.typ) || target == Typ[Invalid] {
+		return
+	}
+
+	// TODO(gri) Sloppy code - clean up. This function is central
+	//           to assignment and expression checking.
+
+	if isUntyped(target) {
+		// both x and target are untyped
+		xkind := x.typ.(*Basic).kind
+		tkind := target.(*Basic).kind
+		if isNumeric(x.typ) && isNumeric(target) {
+			if xkind < tkind {
+				x.typ = target
+				check.updateExprType(x.expr, target, false)
+			}
+		} else if xkind != tkind {
+			goto Error
+		}
+		return
+	}
+
+	// typed target
+	switch t := target.Underlying().(type) {
+	case *Basic:
+		if x.mode == constant_ {
+			check.representable(x, t)
+			if x.mode == invalid {
+				return
+			}
+			// expression value may have been rounded - update if needed
+			check.updateExprVal(x.expr, x.val)
+		} else {
+			// Non-constant untyped values may appear as the
+			// result of comparisons (untyped bool), intermediate
+			// (delayed-checked) rhs operands of shifts, and as
+			// the value nil.
+			switch x.typ.(*Basic).kind {
+			case UntypedBool:
+				if !isBoolean(target) {
+					goto Error
+				}
+			case UntypedInt, UntypedRune, UntypedFloat, UntypedComplex:
+				if !isNumeric(target) {
+					goto Error
+				}
+			case UntypedString:
+				// Non-constant untyped string values are not
+				// permitted by the spec and should not occur.
+				unreachable()
+			case UntypedNil:
+				// Unsafe.Pointer is a basic type that includes nil.
+				if !hasNil(target) {
+					goto Error
+				}
+			default:
+				goto Error
+			}
+		}
+	case *Interface:
+		if !x.isNil() && !t.Empty() /* empty interfaces are ok */ {
+			goto Error
+		}
+		// Update operand types to the default type rather then
+		// the target (interface) type: values must have concrete
+		// dynamic types. If the value is nil, keep it untyped
+		// (this is important for tools such as go vet which need
+		// the dynamic type for argument checking of say, print
+		// functions)
+		if x.isNil() {
+			target = Typ[UntypedNil]
+		} else {
+			// cannot assign untyped values to non-empty interfaces
+			if !t.Empty() {
+				goto Error
+			}
+			target = Default(x.typ)
+		}
+	case *Pointer, *Signature, *Slice, *Map, *Chan:
+		if !x.isNil() {
+			goto Error
+		}
+		// keep nil untyped - see comment for interfaces, above
+		target = Typ[UntypedNil]
+	default:
+		goto Error
+	}
+
+	x.typ = target
+	check.updateExprType(x.expr, target, true) // UntypedNils are final
+	return
+
+Error:
+	check.errorf(x.pos(), "cannot convert %s to %s", x, target)
+	x.mode = invalid
+}
+
+func (check *Checker) comparison(x, y *operand, op token.Token) {
+	// spec: "In any comparison, the first operand must be assignable
+	// to the type of the second operand, or vice versa."
+	err := ""
+	if x.assignableTo(check.conf, y.typ, nil) || y.assignableTo(check.conf, x.typ, nil) {
+		defined := false
+		switch op {
+		case token.EQL, token.NEQ:
+			// spec: "The equality operators == and != apply to operands that are comparable."
+			defined = Comparable(x.typ) || x.isNil() && hasNil(y.typ) || y.isNil() && hasNil(x.typ)
+		case token.LSS, token.LEQ, token.GTR, token.GEQ:
+			// spec: The ordering operators <, <=, >, and >= apply to operands that are ordered."
+			defined = isOrdered(x.typ)
+		default:
+			unreachable()
+		}
+		if !defined {
+			typ := x.typ
+			if x.isNil() {
+				typ = y.typ
+			}
+			err = check.sprintf("operator %s not defined for %s", op, typ)
+		}
+	} else {
+		err = check.sprintf("mismatched types %s and %s", x.typ, y.typ)
+	}
+
+	if err != "" {
+		check.errorf(x.pos(), "cannot compare %s %s %s (%s)", x.expr, op, y.expr, err)
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant_ && y.mode == constant_ {
+		x.val = constant.MakeBool(constant.Compare(x.val, op, y.val))
+		// The operands are never materialized; no need to update
+		// their types.
+	} else {
+		x.mode = value
+		// The operands have now their final types, which at run-
+		// time will be materialized. Update the expression trees.
+		// If the current types are untyped, the materialized type
+		// is the respective default type.
+		check.updateExprType(x.expr, Default(x.typ), true)
+		check.updateExprType(y.expr, Default(y.typ), true)
+	}
+
+	// spec: "Comparison operators compare two operands and yield
+	//        an untyped boolean value."
+	x.typ = Typ[UntypedBool]
+}
+
+func (check *Checker) shift(x, y *operand, e *ast.BinaryExpr, op token.Token) {
+	untypedx := isUntyped(x.typ)
+
+	var xval constant.Value
+	if x.mode == constant_ {
+		xval = constant.ToInt(x.val)
+	}
+
+	if isInteger(x.typ) || untypedx && xval != nil && xval.Kind() == constant.Int {
+		// The lhs is of integer type or an untyped constant representable
+		// as an integer. Nothing to do.
+	} else {
+		// shift has no chance
+		check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
+		x.mode = invalid
+		return
+	}
+
+	// spec: "The right operand in a shift expression must have unsigned
+	// integer type or be an untyped constant representable by a value of
+	// type uint."
+	switch {
+	case isUnsigned(y.typ):
+		// nothing to do
+	case isUntyped(y.typ):
+		check.convertUntyped(y, Typ[Uint])
+		if y.mode == invalid {
+			x.mode = invalid
+			return
+		}
+	default:
+		check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
+		x.mode = invalid
+		return
+	}
+
+	if x.mode == constant_ {
+		if y.mode == constant_ {
+			// rhs must be an integer value
+			yval := constant.ToInt(y.val)
+			if yval.Kind() != constant.Int {
+				check.invalidOp(y.pos(), "shift count %s must be unsigned integer", y)
+				x.mode = invalid
+				return
+			}
+			// rhs must be within reasonable bounds
+			const shiftBound = 1023 - 1 + 52 // so we can express smallestFloat64
+			s, ok := constant.Uint64Val(yval)
+			if !ok || s > shiftBound {
+				check.invalidOp(y.pos(), "invalid shift count %s", y)
+				x.mode = invalid
+				return
+			}
+			// The lhs is representable as an integer but may not be an integer
+			// (e.g., 2.0, an untyped float) - this can only happen for untyped
+			// non-integer numeric constants. Correct the type so that the shift
+			// result is of integer type.
+			if !isInteger(x.typ) {
+				x.typ = Typ[UntypedInt]
+			}
+			// x is a constant so xval != nil and it must be of Int kind.
+			x.val = constant.Shift(xval, op, uint(s))
+			// Typed constants must be representable in
+			// their type after each constant operation.
+			if isTyped(x.typ) {
+				if e != nil {
+					x.expr = e // for better error message
+				}
+				check.representable(x, x.typ.Underlying().(*Basic))
+			}
+			return
+		}
+
+		// non-constant shift with constant lhs
+		if untypedx {
+			// spec: "If the left operand of a non-constant shift
+			// expression is an untyped constant, the type of the
+			// constant is what it would be if the shift expression
+			// were replaced by its left operand alone.".
+			//
+			// Delay operand checking until we know the final type
+			// by marking the lhs expression as lhs shift operand.
+			//
+			// Usually (in correct programs), the lhs expression
+			// is in the untyped map. However, it is possible to
+			// create incorrect programs where the same expression
+			// is evaluated twice (via a declaration cycle) such
+			// that the lhs expression type is determined in the
+			// first round and thus deleted from the map, and then
+			// not found in the second round (double insertion of
+			// the same expr node still just leads to one entry for
+			// that node, and it can only be deleted once).
+			// Be cautious and check for presence of entry.
+			// Example: var e, f = int(1<<""[f]) // issue 11347
+			if info, found := check.untyped[x.expr]; found {
+				info.isLhs = true
+				check.untyped[x.expr] = info
+			}
+			// keep x's type
+			x.mode = value
+			return
+		}
+	}
+
+	// constant rhs must be >= 0
+	if y.mode == constant_ && constant.Sign(y.val) < 0 {
+		check.invalidOp(y.pos(), "shift count %s must not be negative", y)
+	}
+
+	// non-constant shift - lhs must be an integer
+	if !isInteger(x.typ) {
+		check.invalidOp(x.pos(), "shifted operand %s must be integer", x)
+		x.mode = invalid
+		return
+	}
+
+	x.mode = value
+}
+
+var binaryOpPredicates = opPredicates{
+	token.ADD: func(typ Type) bool { return isNumeric(typ) || isString(typ) },
+	token.SUB: isNumeric,
+	token.MUL: isNumeric,
+	token.QUO: isNumeric,
+	token.REM: isInteger,
+
+	token.AND:     isInteger,
+	token.OR:      isInteger,
+	token.XOR:     isInteger,
+	token.AND_NOT: isInteger,
+
+	token.LAND: isBoolean,
+	token.LOR:  isBoolean,
+}
+
+// The binary expression e may be nil. It's passed in for better error messages only.
+func (check *Checker) binary(x *operand, e *ast.BinaryExpr, lhs, rhs ast.Expr, op token.Token) {
+	var y operand
+
+	check.expr(x, lhs)
+	check.expr(&y, rhs)
+
+	if x.mode == invalid {
+		return
+	}
+	if y.mode == invalid {
+		x.mode = invalid
+		x.expr = y.expr
+		return
+	}
+
+	if isShift(op) {
+		check.shift(x, &y, e, op)
+		return
+	}
+
+	check.convertUntyped(x, y.typ)
+	if x.mode == invalid {
+		return
+	}
+	check.convertUntyped(&y, x.typ)
+	if y.mode == invalid {
+		x.mode = invalid
+		return
+	}
+
+	if isComparison(op) {
+		check.comparison(x, &y, op)
+		return
+	}
+
+	if !Identical(x.typ, y.typ) {
+		// only report an error if we have valid types
+		// (otherwise we had an error reported elsewhere already)
+		if x.typ != Typ[Invalid] && y.typ != Typ[Invalid] {
+			check.invalidOp(x.pos(), "mismatched types %s and %s", x.typ, y.typ)
+		}
+		x.mode = invalid
+		return
+	}
+
+	if !check.op(binaryOpPredicates, x, op) {
+		x.mode = invalid
+		return
+	}
+
+	if op == token.QUO || op == token.REM {
+		// check for zero divisor
+		if (x.mode == constant_ || isInteger(x.typ)) && y.mode == constant_ && constant.Sign(y.val) == 0 {
+			check.invalidOp(y.pos(), "division by zero")
+			x.mode = invalid
+			return
+		}
+
+		// check for divisor underflow in complex division (see issue 20227)
+		if x.mode == constant_ && y.mode == constant_ && isComplex(x.typ) {
+			re, im := constant.Real(y.val), constant.Imag(y.val)
+			re2, im2 := constant.BinaryOp(re, token.MUL, re), constant.BinaryOp(im, token.MUL, im)
+			if constant.Sign(re2) == 0 && constant.Sign(im2) == 0 {
+				check.invalidOp(y.pos(), "division by zero")
+				x.mode = invalid
+				return
+			}
+		}
+	}
+
+	if x.mode == constant_ && y.mode == constant_ {
+		xval := x.val
+		yval := y.val
+		typ := x.typ.Underlying().(*Basic)
+		// force integer division of integer operands
+		if op == token.QUO && isInteger(typ) {
+			op = token.QUO_ASSIGN
+		}
+		x.val = constant.BinaryOp(xval, op, yval)
+		// Typed constants must be representable in
+		// their type after each constant operation.
+		if isTyped(typ) {
+			if e != nil {
+				x.expr = e // for better error message
+			}
+			check.representable(x, typ)
+		}
+		return
+	}
+
+	x.mode = value
+	// x.typ is unchanged
+}
+
+// index checks an index expression for validity.
+// If max >= 0, it is the upper bound for index.
+// If index is valid and the result i >= 0, then i is the constant value of index.
+func (check *Checker) index(index ast.Expr, max int64) (i int64, valid bool) {
+	var x operand
+	check.expr(&x, index)
+	if x.mode == invalid {
+		return
+	}
+
+	// an untyped constant must be representable as Int
+	check.convertUntyped(&x, Typ[Int])
+	if x.mode == invalid {
+		return
+	}
+
+	// the index must be of integer type
+	if !isInteger(x.typ) {
+		check.invalidArg(x.pos(), "index %s must be integer", &x)
+		return
+	}
+
+	// a constant index i must be in bounds
+	if x.mode == constant_ {
+		if constant.Sign(x.val) < 0 {
+			check.invalidArg(x.pos(), "index %s must not be negative", &x)
+			return
+		}
+		i, valid = constant.Int64Val(constant.ToInt(x.val))
+		if !valid || max >= 0 && i >= max {
+			check.errorf(x.pos(), "index %s is out of bounds", &x)
+			return i, false
+		}
+		// 0 <= i [ && i < max ]
+		return i, true
+	}
+
+	return -1, true
+}
+
+// indexElts checks the elements (elts) of an array or slice composite literal
+// against the literal's element type (typ), and the element indices against
+// the literal length if known (length >= 0). It returns the length of the
+// literal (maximum index value + 1).
+//
+func (check *Checker) indexedElts(elts []ast.Expr, typ Type, length int64) int64 {
+	visited := make(map[int64]bool, len(elts))
+	var index, max int64
+	for _, e := range elts {
+		// determine and check index
+		validIndex := false
+		eval := e
+		if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
+			if i, ok := check.index(kv.Key, length); ok {
+				if i >= 0 {
+					index = i
+					validIndex = true
+				} else {
+					check.errorf(e.Pos(), "index %s must be integer constant", kv.Key)
+				}
+			}
+			eval = kv.Value
+		} else if length >= 0 && index >= length {
+			check.errorf(e.Pos(), "index %d is out of bounds (>= %d)", index, length)
+		} else {
+			validIndex = true
+		}
+
+		// if we have a valid index, check for duplicate entries
+		if validIndex {
+			if visited[index] {
+				check.errorf(e.Pos(), "duplicate index %d in array or slice literal", index)
+			}
+			visited[index] = true
+		}
+		index++
+		if index > max {
+			max = index
+		}
+
+		// check element against composite literal element type
+		var x operand
+		check.exprWithHint(&x, eval, typ)
+		check.assignment(&x, typ, "array or slice literal")
+	}
+	return max
+}
+
+// exprKind describes the kind of an expression; the kind
+// determines if an expression is valid in 'statement context'.
+type exprKind int
+
+const (
+	conversion exprKind = iota
+	expression
+	statement
+)
+
+// rawExpr typechecks expression e and initializes x with the expression
+// value or type. If an error occurred, x.mode is set to invalid.
+// If hint != nil, it is the type of a composite literal element.
+//
+func (check *Checker) rawExpr(x *operand, e ast.Expr, hint Type) exprKind {
+	if trace {
+		check.trace(e.Pos(), "%s", e)
+		check.indent++
+		defer func() {
+			check.indent--
+			check.trace(e.Pos(), "=> %s", x)
+		}()
+	}
+
+	kind := check.exprInternal(x, e, hint)
+
+	// convert x into a user-friendly set of values
+	// TODO(gri) this code can be simplified
+	var typ Type
+	var val constant.Value
+	switch x.mode {
+	case invalid:
+		typ = Typ[Invalid]
+	case novalue:
+		typ = (*Tuple)(nil)
+	case constant_:
+		typ = x.typ
+		val = x.val
+	default:
+		typ = x.typ
+	}
+	assert(x.expr != nil && typ != nil)
+
+	if isUntyped(typ) {
+		// delay type and value recording until we know the type
+		// or until the end of type checking
+		check.rememberUntyped(x.expr, false, x.mode, typ.(*Basic), val)
+	} else {
+		check.recordTypeAndValue(e, x.mode, typ, val)
+	}
+
+	return kind
+}
+
+// exprInternal contains the core of type checking of expressions.
+// Must only be called by rawExpr.
+//
+func (check *Checker) exprInternal(x *operand, e ast.Expr, hint Type) exprKind {
+	// make sure x has a valid state in case of bailout
+	// (was issue 5770)
+	x.mode = invalid
+	x.typ = Typ[Invalid]
+
+	switch e := e.(type) {
+	case *ast.BadExpr:
+		goto Error // error was reported before
+
+	case *ast.Ident:
+		check.ident(x, e, nil, nil)
+
+	case *ast.Ellipsis:
+		// ellipses are handled explicitly where they are legal
+		// (array composite literals and parameter lists)
+		check.error(e.Pos(), "invalid use of '...'")
+		goto Error
+
+	case *ast.BasicLit:
+		x.setConst(e.Kind, e.Value)
+		if x.mode == invalid {
+			check.invalidAST(e.Pos(), "invalid literal %v", e.Value)
+			goto Error
+		}
+
+	case *ast.FuncLit:
+		if sig, ok := check.typ(e.Type).(*Signature); ok {
+			// Anonymous functions are considered part of the
+			// init expression/func declaration which contains
+			// them: use existing package-level declaration info.
+			//
+			// TODO(gri) We delay type-checking of regular (top-level)
+			//           function bodies until later. Why don't we do
+			//           it for closures of top-level expressions?
+			//           (We can't easily do it for local closures
+			//           because the surrounding scopes must reflect
+			//           the exact position where the closure appears
+			//           in the source; e.g., variables declared below
+			//           must not be visible).
+			check.funcBody(check.decl, "", sig, e.Body)
+			x.mode = value
+			x.typ = sig
+		} else {
+			check.invalidAST(e.Pos(), "invalid function literal %s", e)
+			goto Error
+		}
+
+	case *ast.CompositeLit:
+		var typ, base Type
+
+		switch {
+		case e.Type != nil:
+			// composite literal type present - use it
+			// [...]T array types may only appear with composite literals.
+			// Check for them here so we don't have to handle ... in general.
+			if atyp, _ := e.Type.(*ast.ArrayType); atyp != nil && atyp.Len != nil {
+				if ellip, _ := atyp.Len.(*ast.Ellipsis); ellip != nil && ellip.Elt == nil {
+					// We have an "open" [...]T array type.
+					// Create a new ArrayType with unknown length (-1)
+					// and finish setting it up after analyzing the literal.
+					typ = &Array{len: -1, elem: check.typ(atyp.Elt)}
+					base = typ
+					break
+				}
+			}
+			typ = check.typ(e.Type)
+			base = typ
+
+		case hint != nil:
+			// no composite literal type present - use hint (element type of enclosing type)
+			typ = hint
+			base, _ = deref(typ.Underlying()) // *T implies &T{}
+
+		default:
+			// TODO(gri) provide better error messages depending on context
+			check.error(e.Pos(), "missing type in composite literal")
+			goto Error
+		}
+
+		switch utyp := base.Underlying().(type) {
+		case *Struct:
+			if len(e.Elts) == 0 {
+				break
+			}
+			fields := utyp.fields
+			if _, ok := e.Elts[0].(*ast.KeyValueExpr); ok {
+				// all elements must have keys
+				visited := make([]bool, len(fields))
+				for _, e := range e.Elts {
+					kv, _ := e.(*ast.KeyValueExpr)
+					if kv == nil {
+						check.error(e.Pos(), "mixture of field:value and value elements in struct literal")
+						continue
+					}
+					key, _ := kv.Key.(*ast.Ident)
+					if key == nil {
+						check.errorf(kv.Pos(), "invalid field name %s in struct literal", kv.Key)
+						continue
+					}
+					i := fieldIndex(utyp.fields, check.pkg, key.Name)
+					if i < 0 {
+						check.errorf(kv.Pos(), "unknown field %s in struct literal", key.Name)
+						continue
+					}
+					fld := fields[i]
+					check.recordUse(key, fld)
+					// 0 <= i < len(fields)
+					if visited[i] {
+						check.errorf(kv.Pos(), "duplicate field name %s in struct literal", key.Name)
+						continue
+					}
+					visited[i] = true
+					check.expr(x, kv.Value)
+					etyp := fld.typ
+					check.assignment(x, etyp, "struct literal")
+				}
+			} else {
+				// no element must have a key
+				for i, e := range e.Elts {
+					if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
+						check.error(kv.Pos(), "mixture of field:value and value elements in struct literal")
+						continue
+					}
+					check.expr(x, e)
+					if i >= len(fields) {
+						check.error(x.pos(), "too many values in struct literal")
+						break // cannot continue
+					}
+					// i < len(fields)
+					fld := fields[i]
+					if !fld.Exported() && fld.pkg != check.pkg {
+						check.errorf(x.pos(), "implicit assignment to unexported field %s in %s literal", fld.name, typ)
+						continue
+					}
+					etyp := fld.typ
+					check.assignment(x, etyp, "struct literal")
+				}
+				if len(e.Elts) < len(fields) {
+					check.error(e.Rbrace, "too few values in struct literal")
+					// ok to continue
+				}
+			}
+
+		case *Array:
+			// Prevent crash if the array referred to is not yet set up.
+			// This is a stop-gap solution; a better approach would use the mechanism of
+			// Checker.ident (typexpr.go) using a path of types. But that would require
+			// passing the path everywhere (all expression-checking methods, not just
+			// type expression checking), and we're not set up for that (quite possibly
+			// an indication that cycle detection needs to be rethought). Was issue #18643.
+			if utyp.elem == nil {
+				check.error(e.Pos(), "illegal cycle in type declaration")
+				goto Error
+			}
+			n := check.indexedElts(e.Elts, utyp.elem, utyp.len)
+			// If we have an "open" [...]T array, set the length now that we know it
+			// and record the type for [...] (usually done by check.typExpr which is
+			// not called for [...]).
+			if utyp.len < 0 {
+				utyp.len = n
+				check.recordTypeAndValue(e.Type, typexpr, utyp, nil)
+			}
+
+		case *Slice:
+			// Prevent crash if the slice referred to is not yet set up.
+			// See analogous comment for *Array.
+			if utyp.elem == nil {
+				check.error(e.Pos(), "illegal cycle in type declaration")
+				goto Error
+			}
+			check.indexedElts(e.Elts, utyp.elem, -1)
+
+		case *Map:
+			// Prevent crash if the map referred to is not yet set up.
+			// See analogous comment for *Array.
+			if utyp.key == nil || utyp.elem == nil {
+				check.error(e.Pos(), "illegal cycle in type declaration")
+				goto Error
+			}
+			visited := make(map[interface{}][]Type, len(e.Elts))
+			for _, e := range e.Elts {
+				kv, _ := e.(*ast.KeyValueExpr)
+				if kv == nil {
+					check.error(e.Pos(), "missing key in map literal")
+					continue
+				}
+				check.exprWithHint(x, kv.Key, utyp.key)
+				check.assignment(x, utyp.key, "map literal")
+				if x.mode == invalid {
+					continue
+				}
+				if x.mode == constant_ {
+					duplicate := false
+					// if the key is of interface type, the type is also significant when checking for duplicates
+					xkey := keyVal(x.val)
+					if _, ok := utyp.key.Underlying().(*Interface); ok {
+						for _, vtyp := range visited[xkey] {
+							if Identical(vtyp, x.typ) {
+								duplicate = true
+								break
+							}
+						}
+						visited[xkey] = append(visited[xkey], x.typ)
+					} else {
+						_, duplicate = visited[xkey]
+						visited[xkey] = nil
+					}
+					if duplicate {
+						check.errorf(x.pos(), "duplicate key %s in map literal", x.val)
+						continue
+					}
+				}
+				check.exprWithHint(x, kv.Value, utyp.elem)
+				check.assignment(x, utyp.elem, "map literal")
+			}
+
+		default:
+			// when "using" all elements unpack KeyValueExpr
+			// explicitly because check.use doesn't accept them
+			for _, e := range e.Elts {
+				if kv, _ := e.(*ast.KeyValueExpr); kv != nil {
+					// Ideally, we should also "use" kv.Key but we can't know
+					// if it's an externally defined struct key or not. Going
+					// forward anyway can lead to other errors. Give up instead.
+					e = kv.Value
+				}
+				check.use(e)
+			}
+			// if utyp is invalid, an error was reported before
+			if utyp != Typ[Invalid] {
+				check.errorf(e.Pos(), "invalid composite literal type %s", typ)
+				goto Error
+			}
+		}
+
+		x.mode = value
+		x.typ = typ
+
+	case *ast.ParenExpr:
+		kind := check.rawExpr(x, e.X, nil)
+		x.expr = e
+		return kind
+
+	case *ast.SelectorExpr:
+		check.selector(x, e)
+
+	case *ast.IndexExpr:
+		check.expr(x, e.X)
+		if x.mode == invalid {
+			check.use(e.Index)
+			goto Error
+		}
+
+		valid := false
+		length := int64(-1) // valid if >= 0
+		switch typ := x.typ.Underlying().(type) {
+		case *Basic:
+			if isString(typ) {
+				valid = true
+				if x.mode == constant_ {
+					length = int64(len(constant.StringVal(x.val)))
+				}
+				// an indexed string always yields a byte value
+				// (not a constant) even if the string and the
+				// index are constant
+				x.mode = value
+				x.typ = universeByte // use 'byte' name
+			}
+
+		case *Array:
+			valid = true
+			length = typ.len
+			if x.mode != variable {
+				x.mode = value
+			}
+			x.typ = typ.elem
+
+		case *Pointer:
+			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
+				valid = true
+				length = typ.len
+				x.mode = variable
+				x.typ = typ.elem
+			}
+
+		case *Slice:
+			valid = true
+			x.mode = variable
+			x.typ = typ.elem
+
+		case *Map:
+			var key operand
+			check.expr(&key, e.Index)
+			check.assignment(&key, typ.key, "map index")
+			if x.mode == invalid {
+				goto Error
+			}
+			x.mode = mapindex
+			x.typ = typ.elem
+			x.expr = e
+			return expression
+		}
+
+		if !valid {
+			check.invalidOp(x.pos(), "cannot index %s", x)
+			goto Error
+		}
+
+		if e.Index == nil {
+			check.invalidAST(e.Pos(), "missing index for %s", x)
+			goto Error
+		}
+
+		check.index(e.Index, length)
+		// ok to continue
+
+	case *ast.SliceExpr:
+		check.expr(x, e.X)
+		if x.mode == invalid {
+			check.use(e.Low, e.High, e.Max)
+			goto Error
+		}
+
+		valid := false
+		length := int64(-1) // valid if >= 0
+		switch typ := x.typ.Underlying().(type) {
+		case *Basic:
+			if isString(typ) {
+				if e.Slice3 {
+					check.invalidOp(x.pos(), "3-index slice of string")
+					goto Error
+				}
+				valid = true
+				if x.mode == constant_ {
+					length = int64(len(constant.StringVal(x.val)))
+				}
+				// spec: "For untyped string operands the result
+				// is a non-constant value of type string."
+				if typ.kind == UntypedString {
+					x.typ = Typ[String]
+				}
+			}
+
+		case *Array:
+			valid = true
+			length = typ.len
+			if x.mode != variable {
+				check.invalidOp(x.pos(), "cannot slice %s (value not addressable)", x)
+				goto Error
+			}
+			x.typ = &Slice{elem: typ.elem}
+
+		case *Pointer:
+			if typ, _ := typ.base.Underlying().(*Array); typ != nil {
+				valid = true
+				length = typ.len
+				x.typ = &Slice{elem: typ.elem}
+			}
+
+		case *Slice:
+			valid = true
+			// x.typ doesn't change
+		}
+
+		if !valid {
+			check.invalidOp(x.pos(), "cannot slice %s", x)
+			goto Error
+		}
+
+		x.mode = value
+
+		// spec: "Only the first index may be omitted; it defaults to 0."
+		if e.Slice3 && (e.High == nil || e.Max == nil) {
+			check.error(e.Rbrack, "2nd and 3rd index required in 3-index slice")
+			goto Error
+		}
+
+		// check indices
+		var ind [3]int64
+		for i, expr := range []ast.Expr{e.Low, e.High, e.Max} {
+			x := int64(-1)
+			switch {
+			case expr != nil:
+				// The "capacity" is only known statically for strings, arrays,
+				// and pointers to arrays, and it is the same as the length for
+				// those types.
+				max := int64(-1)
+				if length >= 0 {
+					max = length + 1
+				}
+				if t, ok := check.index(expr, max); ok && t >= 0 {
+					x = t
+				}
+			case i == 0:
+				// default is 0 for the first index
+				x = 0
+			case length >= 0:
+				// default is length (== capacity) otherwise
+				x = length
+			}
+			ind[i] = x
+		}
+
+		// constant indices must be in range
+		// (check.index already checks that existing indices >= 0)
+	L:
+		for i, x := range ind[:len(ind)-1] {
+			if x > 0 {
+				for _, y := range ind[i+1:] {
+					if y >= 0 && x > y {
+						check.errorf(e.Rbrack, "invalid slice indices: %d > %d", x, y)
+						break L // only report one error, ok to continue
+					}
+				}
+			}
+		}
+
+	case *ast.TypeAssertExpr:
+		check.expr(x, e.X)
+		if x.mode == invalid {
+			goto Error
+		}
+		xtyp, _ := x.typ.Underlying().(*Interface)
+		if xtyp == nil {
+			check.invalidOp(x.pos(), "%s is not an interface", x)
+			goto Error
+		}
+		// x.(type) expressions are handled explicitly in type switches
+		if e.Type == nil {
+			check.invalidAST(e.Pos(), "use of .(type) outside type switch")
+			goto Error
+		}
+		T := check.typ(e.Type)
+		if T == Typ[Invalid] {
+			goto Error
+		}
+		check.typeAssertion(x.pos(), x, xtyp, T)
+		x.mode = commaok
+		x.typ = T
+
+	case *ast.CallExpr:
+		return check.call(x, e)
+
+	case *ast.StarExpr:
+		check.exprOrType(x, e.X)
+		switch x.mode {
+		case invalid:
+			goto Error
+		case typexpr:
+			x.typ = &Pointer{base: x.typ}
+		default:
+			if typ, ok := x.typ.Underlying().(*Pointer); ok {
+				x.mode = variable
+				x.typ = typ.base
+			} else {
+				check.invalidOp(x.pos(), "cannot indirect %s", x)
+				goto Error
+			}
+		}
+
+	case *ast.UnaryExpr:
+		check.expr(x, e.X)
+		if x.mode == invalid {
+			goto Error
+		}
+		check.unary(x, e, e.Op)
+		if x.mode == invalid {
+			goto Error
+		}
+		if e.Op == token.ARROW {
+			x.expr = e
+			return statement // receive operations may appear in statement context
+		}
+
+	case *ast.BinaryExpr:
+		check.binary(x, e, e.X, e.Y, e.Op)
+		if x.mode == invalid {
+			goto Error
+		}
+
+	case *ast.KeyValueExpr:
+		// key:value expressions are handled in composite literals
+		check.invalidAST(e.Pos(), "no key:value expected")
+		goto Error
+
+	case *ast.ArrayType, *ast.StructType, *ast.FuncType,
+		*ast.InterfaceType, *ast.MapType, *ast.ChanType:
+		x.mode = typexpr
+		x.typ = check.typ(e)
+		// Note: rawExpr (caller of exprInternal) will call check.recordTypeAndValue
+		// even though check.typ has already called it. This is fine as both
+		// times the same expression and type are recorded. It is also not a
+		// performance issue because we only reach here for composite literal
+		// types, which are comparatively rare.
+
+	default:
+		panic(fmt.Sprintf("%s: unknown expression type %T", check.fset.Position(e.Pos()), e))
+	}
+
+	// everything went well
+	x.expr = e
+	return expression
+
+Error:
+	x.mode = invalid
+	x.expr = e
+	return statement // avoid follow-up errors
+}
+
+func keyVal(x constant.Value) interface{} {
+	switch x.Kind() {
+	case constant.Bool:
+		return constant.BoolVal(x)
+	case constant.String:
+		return constant.StringVal(x)
+	case constant.Int:
+		if v, ok := constant.Int64Val(x); ok {
+			return v
+		}
+		if v, ok := constant.Uint64Val(x); ok {
+			return v
+		}
+	case constant.Float:
+		v, _ := constant.Float64Val(x)
+		return v
+	case constant.Complex:
+		r, _ := constant.Float64Val(constant.Real(x))
+		i, _ := constant.Float64Val(constant.Imag(x))
+		return complex(r, i)
+	}
+	return x
+}
+
+// typeAssertion checks that x.(T) is legal; xtyp must be the type of x.
+func (check *Checker) typeAssertion(pos token.Pos, x *operand, xtyp *Interface, T Type) {
+	method, wrongType := assertableTo(xtyp, T)
+	if method == nil {
+		return
+	}
+
+	var msg string
+	if wrongType {
+		msg = "wrong type for method"
+	} else {
+		msg = "missing method"
+	}
+	check.errorf(pos, "%s cannot have dynamic type %s (%s %s)", x, T, msg, method.name)
+}
+
+func (check *Checker) singleValue(x *operand) {
+	if x.mode == value {
+		// tuple types are never named - no need for underlying type below
+		if t, ok := x.typ.(*Tuple); ok {
+			assert(t.Len() != 1)
+			check.errorf(x.pos(), "%d-valued %s where single value is expected", t.Len(), x)
+			x.mode = invalid
+		}
+	}
+}
+
+// expr typechecks expression e and initializes x with the expression value.
+// The result must be a single value.
+// If an error occurred, x.mode is set to invalid.
+//
+func (check *Checker) expr(x *operand, e ast.Expr) {
+	check.multiExpr(x, e)
+	check.singleValue(x)
+}
+
+// multiExpr is like expr but the result may be a multi-value.
+func (check *Checker) multiExpr(x *operand, e ast.Expr) {
+	check.rawExpr(x, e, nil)
+	var msg string
+	switch x.mode {
+	default:
+		return
+	case novalue:
+		msg = "%s used as value"
+	case builtin:
+		msg = "%s must be called"
+	case typexpr:
+		msg = "%s is not an expression"
+	}
+	check.errorf(x.pos(), msg, x)
+	x.mode = invalid
+}
+
+// exprWithHint typechecks expression e and initializes x with the expression value;
+// hint is the type of a composite literal element.
+// If an error occurred, x.mode is set to invalid.
+//
+func (check *Checker) exprWithHint(x *operand, e ast.Expr, hint Type) {
+	assert(hint != nil)
+	check.rawExpr(x, e, hint)
+	check.singleValue(x)
+	var msg string
+	switch x.mode {
+	default:
+		return
+	case novalue:
+		msg = "%s used as value"
+	case builtin:
+		msg = "%s must be called"
+	case typexpr:
+		msg = "%s is not an expression"
+	}
+	check.errorf(x.pos(), msg, x)
+	x.mode = invalid
+}
+
+// exprOrType typechecks expression or type e and initializes x with the expression value or type.
+// If an error occurred, x.mode is set to invalid.
+//
+func (check *Checker) exprOrType(x *operand, e ast.Expr) {
+	check.rawExpr(x, e, nil)
+	check.singleValue(x)
+	if x.mode == novalue {
+		check.errorf(x.pos(), "%s used as value or type", x)
+		x.mode = invalid
+	}
+}

third_party/forked/golang/go/types/exprstring.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements printing of expressions.
+
+package types
+
+import (
+	"bytes"
+	"go/ast"
+)
+
+// ExprString returns the (possibly shortened) string representation for x.
+// Shortened representations are suitable for user interfaces but may not
+// necessarily follow Go syntax.
+func ExprString(x ast.Expr) string {
+	var buf bytes.Buffer
+	WriteExpr(&buf, x)
+	return buf.String()
+}
+
+// WriteExpr writes the (possibly shortened) string representation for x to buf.
+// Shortened representations are suitable for user interfaces but may not
+// necessarily follow Go syntax.
+func WriteExpr(buf *bytes.Buffer, x ast.Expr) {
+	// The AST preserves source-level parentheses so there is
+	// no need to introduce them here to correct for different
+	// operator precedences. (This assumes that the AST was
+	// generated by a Go parser.)
+
+	switch x := x.(type) {
+	default:
+		buf.WriteString("(bad expr)") // nil, ast.BadExpr, ast.KeyValueExpr
+
+	case *ast.Ident:
+		buf.WriteString(x.Name)
+
+	case *ast.Ellipsis:
+		buf.WriteString("...")
+		if x.Elt != nil {
+			WriteExpr(buf, x.Elt)
+		}
+
+	case *ast.BasicLit:
+		buf.WriteString(x.Value)
+
+	case *ast.FuncLit:
+		buf.WriteByte('(')
+		WriteExpr(buf, x.Type)
+		buf.WriteString(" literal)") // shortened
+
+	case *ast.CompositeLit:
+		buf.WriteByte('(')
+		WriteExpr(buf, x.Type)
+		buf.WriteString(" literal)") // shortened
+
+	case *ast.ParenExpr:
+		buf.WriteByte('(')
+		WriteExpr(buf, x.X)
+		buf.WriteByte(')')
+
+	case *ast.SelectorExpr:
+		WriteExpr(buf, x.X)
+		buf.WriteByte('.')
+		buf.WriteString(x.Sel.Name)
+
+	case *ast.IndexExpr:
+		WriteExpr(buf, x.X)
+		buf.WriteByte('[')
+		WriteExpr(buf, x.Index)
+		buf.WriteByte(']')
+
+	case *ast.SliceExpr:
+		WriteExpr(buf, x.X)
+		buf.WriteByte('[')
+		if x.Low != nil {
+			WriteExpr(buf, x.Low)
+		}
+		buf.WriteByte(':')
+		if x.High != nil {
+			WriteExpr(buf, x.High)
+		}
+		if x.Slice3 {
+			buf.WriteByte(':')
+			if x.Max != nil {
+				WriteExpr(buf, x.Max)
+			}
+		}
+		buf.WriteByte(']')
+
+	case *ast.TypeAssertExpr:
+		WriteExpr(buf, x.X)
+		buf.WriteString(".(")
+		WriteExpr(buf, x.Type)
+		buf.WriteByte(')')
+
+	case *ast.CallExpr:
+		WriteExpr(buf, x.Fun)
+		buf.WriteByte('(')
+		for i, arg := range x.Args {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			WriteExpr(buf, arg)
+		}
+		if x.Ellipsis.IsValid() {
+			buf.WriteString("...")
+		}
+		buf.WriteByte(')')
+
+	case *ast.StarExpr:
+		buf.WriteByte('*')
+		WriteExpr(buf, x.X)
+
+	case *ast.UnaryExpr:
+		buf.WriteString(x.Op.String())
+		WriteExpr(buf, x.X)
+
+	case *ast.BinaryExpr:
+		WriteExpr(buf, x.X)
+		buf.WriteByte(' ')
+		buf.WriteString(x.Op.String())
+		buf.WriteByte(' ')
+		WriteExpr(buf, x.Y)
+
+	case *ast.ArrayType:
+		buf.WriteByte('[')
+		if x.Len != nil {
+			WriteExpr(buf, x.Len)
+		}
+		buf.WriteByte(']')
+		WriteExpr(buf, x.Elt)
+
+	case *ast.StructType:
+		buf.WriteString("struct{")
+		writeFieldList(buf, x.Fields, "; ", false)
+		buf.WriteByte('}')
+
+	case *ast.FuncType:
+		buf.WriteString("func")
+		writeSigExpr(buf, x)
+
+	case *ast.InterfaceType:
+		buf.WriteString("interface{")
+		writeFieldList(buf, x.Methods, "; ", true)
+		buf.WriteByte('}')
+
+	case *ast.MapType:
+		buf.WriteString("map[")
+		WriteExpr(buf, x.Key)
+		buf.WriteByte(']')
+		WriteExpr(buf, x.Value)
+
+	case *ast.ChanType:
+		var s string
+		switch x.Dir {
+		case ast.SEND:
+			s = "chan<- "
+		case ast.RECV:
+			s = "<-chan "
+		default:
+			s = "chan "
+		}
+		buf.WriteString(s)
+		WriteExpr(buf, x.Value)
+	}
+}
+
+func writeSigExpr(buf *bytes.Buffer, sig *ast.FuncType) {
+	buf.WriteByte('(')
+	writeFieldList(buf, sig.Params, ", ", false)
+	buf.WriteByte(')')
+
+	res := sig.Results
+	n := res.NumFields()
+	if n == 0 {
+		// no result
+		return
+	}
+
+	buf.WriteByte(' ')
+	if n == 1 && len(res.List[0].Names) == 0 {
+		// single unnamed result
+		WriteExpr(buf, res.List[0].Type)
+		return
+	}
+
+	// multiple or named result(s)
+	buf.WriteByte('(')
+	writeFieldList(buf, res, ", ", false)
+	buf.WriteByte(')')
+}
+
+func writeFieldList(buf *bytes.Buffer, fields *ast.FieldList, sep string, iface bool) {
+	for i, f := range fields.List {
+		if i > 0 {
+			buf.WriteString(sep)
+		}
+
+		// field list names
+		for i, name := range f.Names {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			buf.WriteString(name.Name)
+		}
+
+		// types of interface methods consist of signatures only
+		if sig, _ := f.Type.(*ast.FuncType); sig != nil && iface {
+			writeSigExpr(buf, sig)
+			continue
+		}
+
+		// named fields are separated with a blank from the field type
+		if len(f.Names) > 0 {
+			buf.WriteByte(' ')
+		}
+
+		WriteExpr(buf, f.Type)
+
+		// ignore tag
+	}
+}

third_party/forked/golang/go/types/gotype.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build ignore
+
+// Build this command explicitly: go build gotype.go
+
+/*
+The gotype command, like the front-end of a Go compiler, parses and
+type-checks a single Go package. Errors are reported if the analysis
+fails; otherwise gotype is quiet (unless -v is set).
+
+Without a list of paths, gotype reads from standard input, which
+must provide a single Go source file defining a complete package.
+
+With a single directory argument, gotype checks the Go files in
+that directory, comprising a single package. Use -t to include the
+(in-package) _test.go files. Use -x to type check only external
+test files.
+
+Otherwise, each path must be the filename of a Go file belonging
+to the same package.
+
+Imports are processed by importing directly from the source of
+imported packages (default), or by importing from compiled and
+installed packages (by setting -c to the respective compiler).
+
+The -c flag must be set to a compiler ("gc", "gccgo") when type-
+checking packages containing imports with relative import paths
+(import "./mypkg") because the source importer cannot know which
+files to include for such packages.
+
+Usage:
+	gotype [flags] [path...]
+
+The flags are:
+	-t
+		include local test files in a directory (ignored if -x is provided)
+	-x
+		consider only external test files in a directory
+	-e
+		report all errors (not just the first 10)
+	-v
+		verbose mode
+	-c
+		compiler used for installed packages (gc, gccgo, or source); default: source
+
+Flags controlling additional output:
+	-ast
+		print AST (forces -seq)
+	-trace
+		print parse trace (forces -seq)
+	-comments
+		parse comments (ignored unless -ast or -trace is provided)
+
+Examples:
+
+To check the files a.go, b.go, and c.go:
+
+	gotype a.go b.go c.go
+
+To check an entire package including (in-package) tests in the directory dir and print the processed files:
+
+	gotype -t -v dir
+
+To check the external test package (if any) in the current directory, based on installed packages compiled with
+cmd/compile:
+
+	gotype -c=gc -x .
+
+To verify the output of a pipe:
+
+	echo "package foo" | gotype
+
+*/
+package main
+
+import (
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/build"
+	"go/importer"
+	"go/parser"
+	"go/scanner"
+	"go/token"
+	"go/types"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"sync"
+	"time"
+)
+
+var (
+	// main operation modes
+	testFiles  = flag.Bool("t", false, "include in-package test files in a directory")
+	xtestFiles = flag.Bool("x", false, "consider only external test files in a directory")
+	allErrors  = flag.Bool("e", false, "report all errors, not just the first 10")
+	verbose    = flag.Bool("v", false, "verbose mode")
+	compiler   = flag.String("c", "source", "compiler used for installed packages (gc, gccgo, or source)")
+
+	// additional output control
+	printAST      = flag.Bool("ast", false, "print AST (forces -seq)")
+	printTrace    = flag.Bool("trace", false, "print parse trace (forces -seq)")
+	parseComments = flag.Bool("comments", false, "parse comments (ignored unless -ast or -trace is provided)")
+)
+
+var (
+	fset       = token.NewFileSet()
+	errorCount = 0
+	sequential = false
+	parserMode parser.Mode
+)
+
+func initParserMode() {
+	if *allErrors {
+		parserMode |= parser.AllErrors
+	}
+	if *printAST {
+		sequential = true
+	}
+	if *printTrace {
+		parserMode |= parser.Trace
+		sequential = true
+	}
+	if *parseComments && (*printAST || *printTrace) {
+		parserMode |= parser.ParseComments
+	}
+}
+
+const usageString = `usage: gotype [flags] [path ...]
+
+The gotype command, like the front-end of a Go compiler, parses and
+type-checks a single Go package. Errors are reported if the analysis
+fails; otherwise gotype is quiet (unless -v is set).
+
+Without a list of paths, gotype reads from standard input, which
+must provide a single Go source file defining a complete package.
+
+With a single directory argument, gotype checks the Go files in
+that directory, comprising a single package. Use -t to include the
+(in-package) _test.go files. Use -x to type check only external
+test files.
+
+Otherwise, each path must be the filename of a Go file belonging
+to the same package.
+
+Imports are processed by importing directly from the source of
+imported packages (default), or by importing from compiled and
+installed packages (by setting -c to the respective compiler).
+
+The -c flag must be set to a compiler ("gc", "gccgo") when type-
+checking packages containing imports with relative import paths
+(import "./mypkg") because the source importer cannot know which
+files to include for such packages.
+`
+
+func usage() {
+	fmt.Fprintln(os.Stderr, usageString)
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func report(err error) {
+	scanner.PrintError(os.Stderr, err)
+	if list, ok := err.(scanner.ErrorList); ok {
+		errorCount += len(list)
+		return
+	}
+	errorCount++
+}
+
+// parse may be called concurrently
+func parse(filename string, src interface{}) (*ast.File, error) {
+	if *verbose {
+		fmt.Println(filename)
+	}
+	file, err := parser.ParseFile(fset, filename, src, parserMode) // ok to access fset concurrently
+	if *printAST {
+		ast.Print(fset, file)
+	}
+	return file, err
+}
+
+func parseStdin() (*ast.File, error) {
+	src, err := ioutil.ReadAll(os.Stdin)
+	if err != nil {
+		return nil, err
+	}
+	return parse("<standard input>", src)
+}
+
+func parseFiles(dir string, filenames []string) ([]*ast.File, error) {
+	files := make([]*ast.File, len(filenames))
+	errors := make([]error, len(filenames))
+
+	var wg sync.WaitGroup
+	for i, filename := range filenames {
+		wg.Add(1)
+		go func(i int, filepath string) {
+			defer wg.Done()
+			files[i], errors[i] = parse(filepath, nil)
+		}(i, filepath.Join(dir, filename))
+		if sequential {
+			wg.Wait()
+		}
+	}
+	wg.Wait()
+
+	// if there are errors, return the first one for deterministic results
+	for _, err := range errors {
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return files, nil
+}
+
+func parseDir(dir string) ([]*ast.File, error) {
+	ctxt := build.Default
+	pkginfo, err := ctxt.ImportDir(dir, 0)
+	if _, nogo := err.(*build.NoGoError); err != nil && !nogo {
+		return nil, err
+	}
+
+	if *xtestFiles {
+		return parseFiles(dir, pkginfo.XTestGoFiles)
+	}
+
+	filenames := append(pkginfo.GoFiles, pkginfo.CgoFiles...)
+	if *testFiles {
+		filenames = append(filenames, pkginfo.TestGoFiles...)
+	}
+	return parseFiles(dir, filenames)
+}
+
+func getPkgFiles(args []string) ([]*ast.File, error) {
+	if len(args) == 0 {
+		// stdin
+		file, err := parseStdin()
+		if err != nil {
+			return nil, err
+		}
+		return []*ast.File{file}, nil
+	}
+
+	if len(args) == 1 {
+		// possibly a directory
+		path := args[0]
+		info, err := os.Stat(path)
+		if err != nil {
+			return nil, err
+		}
+		if info.IsDir() {
+			return parseDir(path)
+		}
+	}
+
+	// list of files
+	return parseFiles("", args)
+}
+
+func checkPkgFiles(files []*ast.File) {
+	type bailout struct{}
+
+	// if checkPkgFiles is called multiple times, set up conf only once
+	conf := types.Config{
+		FakeImportC: true,
+		Error: func(err error) {
+			if !*allErrors && errorCount >= 10 {
+				panic(bailout{})
+			}
+			report(err)
+		},
+		Importer: importer.For(*compiler, nil),
+		Sizes:    types.SizesFor(build.Default.Compiler, build.Default.GOARCH),
+	}
+
+	defer func() {
+		switch p := recover().(type) {
+		case nil, bailout:
+			// normal return or early exit
+		default:
+			// re-panic
+			panic(p)
+		}
+	}()
+
+	const path = "pkg" // any non-empty string will do for now
+	conf.Check(path, fset, files, nil)
+}
+
+func printStats(d time.Duration) {
+	fileCount := 0
+	lineCount := 0
+	fset.Iterate(func(f *token.File) bool {
+		fileCount++
+		lineCount += f.LineCount()
+		return true
+	})
+
+	fmt.Printf(
+		"%s (%d files, %d lines, %d lines/s)\n",
+		d, fileCount, lineCount, int64(float64(lineCount)/d.Seconds()),
+	)
+}
+
+func main() {
+	flag.Usage = usage
+	flag.Parse()
+	initParserMode()
+
+	start := time.Now()
+
+	files, err := getPkgFiles(flag.Args())
+	if err != nil {
+		report(err)
+		os.Exit(2)
+	}
+
+	checkPkgFiles(files)
+	if errorCount > 0 {
+		os.Exit(2)
+	}
+
+	if *verbose {
+		printStats(time.Since(start))
+	}
+}

third_party/forked/golang/go/types/initorder.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"container/heap"
+	"fmt"
+)
+
+// initOrder computes the Info.InitOrder for package variables.
+func (check *Checker) initOrder() {
+	// An InitOrder may already have been computed if a package is
+	// built from several calls to (*Checker).Files. Clear it.
+	check.Info.InitOrder = check.Info.InitOrder[:0]
+
+	// Compute the object dependency graph and initialize
+	// a priority queue with the list of graph nodes.
+	pq := nodeQueue(dependencyGraph(check.objMap))
+	heap.Init(&pq)
+
+	const debug = false
+	if debug {
+		fmt.Printf("Computing initialization order for %s\n\n", check.pkg)
+		fmt.Println("Object dependency graph:")
+		for obj, d := range check.objMap {
+			// only print objects that may appear in the dependency graph
+			if obj, _ := obj.(dependency); obj != nil {
+				if len(d.deps) > 0 {
+					fmt.Printf("\t%s depends on\n", obj.Name())
+					for dep := range d.deps {
+						fmt.Printf("\t\t%s\n", dep.Name())
+					}
+				} else {
+					fmt.Printf("\t%s has no dependencies\n", obj.Name())
+				}
+			}
+		}
+		fmt.Println()
+
+		fmt.Println("Transposed object dependency graph (functions eliminated):")
+		for _, n := range pq {
+			fmt.Printf("\t%s depends on %d nodes\n", n.obj.Name(), n.ndeps)
+			for p := range n.pred {
+				fmt.Printf("\t\t%s is dependent\n", p.obj.Name())
+			}
+		}
+		fmt.Println()
+
+		fmt.Println("Processing nodes:")
+	}
+
+	// Determine initialization order by removing the highest priority node
+	// (the one with the fewest dependencies) and its edges from the graph,
+	// repeatedly, until there are no nodes left.
+	// In a valid Go program, those nodes always have zero dependencies (after
+	// removing all incoming dependencies), otherwise there are initialization
+	// cycles.
+	emitted := make(map[*declInfo]bool)
+	for len(pq) > 0 {
+		// get the next node
+		n := heap.Pop(&pq).(*graphNode)
+
+		if debug {
+			fmt.Printf("\t%s (src pos %d) depends on %d nodes now\n",
+				n.obj.Name(), n.obj.order(), n.ndeps)
+		}
+
+		// if n still depends on other nodes, we have a cycle
+		if n.ndeps > 0 {
+			cycle := findPath(check.objMap, n.obj, n.obj, make(objSet))
+			// If n.obj is not part of the cycle (e.g., n.obj->b->c->d->c),
+			// cycle will be nil. Don't report anything in that case since
+			// the cycle is reported when the algorithm gets to an object
+			// in the cycle.
+			// Furthermore, once an object in the cycle is encountered,
+			// the cycle will be broken (dependency count will be reduced
+			// below), and so the remaining nodes in the cycle don't trigger
+			// another error (unless they are part of multiple cycles).
+			if cycle != nil {
+				check.reportCycle(cycle)
+			}
+			// Ok to continue, but the variable initialization order
+			// will be incorrect at this point since it assumes no
+			// cycle errors.
+		}
+
+		// reduce dependency count of all dependent nodes
+		// and update priority queue
+		for p := range n.pred {
+			p.ndeps--
+			heap.Fix(&pq, p.index)
+		}
+
+		// record the init order for variables with initializers only
+		v, _ := n.obj.(*Var)
+		info := check.objMap[v]
+		if v == nil || !info.hasInitializer() {
+			continue
+		}
+
+		// n:1 variable declarations such as: a, b = f()
+		// introduce a node for each lhs variable (here: a, b);
+		// but they all have the same initializer - emit only
+		// one, for the first variable seen
+		if emitted[info] {
+			continue // initializer already emitted, if any
+		}
+		emitted[info] = true
+
+		infoLhs := info.lhs // possibly nil (see declInfo.lhs field comment)
+		if infoLhs == nil {
+			infoLhs = []*Var{v}
+		}
+		init := &Initializer{infoLhs, info.init}
+		check.Info.InitOrder = append(check.Info.InitOrder, init)
+	}
+
+	if debug {
+		fmt.Println()
+		fmt.Println("Initialization order:")
+		for _, init := range check.Info.InitOrder {
+			fmt.Printf("\t%s\n", init)
+		}
+		fmt.Println()
+	}
+}
+
+// findPath returns the (reversed) list of objects []Object{to, ... from}
+// such that there is a path of object dependencies from 'from' to 'to'.
+// If there is no such path, the result is nil.
+func findPath(objMap map[Object]*declInfo, from, to Object, visited objSet) []Object {
+	if visited[from] {
+		return nil // node already seen
+	}
+	visited[from] = true
+
+	for d := range objMap[from].deps {
+		if d == to {
+			return []Object{d}
+		}
+		if P := findPath(objMap, d, to, visited); P != nil {
+			return append(P, d)
+		}
+	}
+
+	return nil
+}
+
+// reportCycle reports an error for the given cycle.
+func (check *Checker) reportCycle(cycle []Object) {
+	obj := cycle[0]
+	check.errorf(obj.Pos(), "initialization cycle for %s", obj.Name())
+	// subtle loop: print cycle[i] for i = 0, n-1, n-2, ... 1 for len(cycle) = n
+	for i := len(cycle) - 1; i >= 0; i-- {
+		check.errorf(obj.Pos(), "\t%s refers to", obj.Name()) // secondary error, \t indented
+		obj = cycle[i]
+	}
+	// print cycle[0] again to close the cycle
+	check.errorf(obj.Pos(), "\t%s", obj.Name())
+}
+
+// ----------------------------------------------------------------------------
+// Object dependency graph
+
+// A dependency is an object that may be a dependency in an initialization
+// expression. Only constants, variables, and functions can be dependencies.
+// Constants are here because constant expression cycles are reported during
+// initialization order computation.
+type dependency interface {
+	Object
+	isDependency()
+}
+
+// A graphNode represents a node in the object dependency graph.
+// Each node p in n.pred represents an edge p->n, and each node
+// s in n.succ represents an edge n->s; with a->b indicating that
+// a depends on b.
+type graphNode struct {
+	obj        dependency // object represented by this node
+	pred, succ nodeSet    // consumers and dependencies of this node (lazily initialized)
+	index      int        // node index in graph slice/priority queue
+	ndeps      int        // number of outstanding dependencies before this object can be initialized
+}
+
+type nodeSet map[*graphNode]bool
+
+func (s *nodeSet) add(p *graphNode) {
+	if *s == nil {
+		*s = make(nodeSet)
+	}
+	(*s)[p] = true
+}
+
+// dependencyGraph computes the object dependency graph from the given objMap,
+// with any function nodes removed. The resulting graph contains only constants
+// and variables.
+func dependencyGraph(objMap map[Object]*declInfo) []*graphNode {
+	// M is the dependency (Object) -> graphNode mapping
+	M := make(map[dependency]*graphNode)
+	for obj := range objMap {
+		// only consider nodes that may be an initialization dependency
+		if obj, _ := obj.(dependency); obj != nil {
+			M[obj] = &graphNode{obj: obj}
+		}
+	}
+
+	// compute edges for graph M
+	// (We need to include all nodes, even isolated ones, because they still need
+	// to be scheduled for initialization in correct order relative to other nodes.)
+	for obj, n := range M {
+		// for each dependency obj -> d (= deps[i]), create graph edges n->s and s->n
+		for d := range objMap[obj].deps {
+			// only consider nodes that may be an initialization dependency
+			if d, _ := d.(dependency); d != nil {
+				d := M[d]
+				n.succ.add(d)
+				d.pred.add(n)
+			}
+		}
+	}
+
+	// remove function nodes and collect remaining graph nodes in G
+	// (Mutually recursive functions may introduce cycles among themselves
+	// which are permitted. Yet such cycles may incorrectly inflate the dependency
+	// count for variables which in turn may not get scheduled for initialization
+	// in correct order.)
+	var G []*graphNode
+	for obj, n := range M {
+		if _, ok := obj.(*Func); ok {
+			// connect each predecessor p of n with each successor s
+			// and drop the function node (don't collect it in G)
+			for p := range n.pred {
+				// ignore self-cycles
+				if p != n {
+					// Each successor s of n becomes a successor of p, and
+					// each predecessor p of n becomes a predecessor of s.
+					for s := range n.succ {
+						// ignore self-cycles
+						if s != n {
+							p.succ.add(s)
+							s.pred.add(p)
+							delete(s.pred, n) // remove edge to n
+						}
+					}
+					delete(p.succ, n) // remove edge to n
+				}
+			}
+		} else {
+			// collect non-function nodes
+			G = append(G, n)
+		}
+	}
+
+	// fill in index and ndeps fields
+	for i, n := range G {
+		n.index = i
+		n.ndeps = len(n.succ)
+	}
+
+	return G
+}
+
+// ----------------------------------------------------------------------------
+// Priority queue
+
+// nodeQueue implements the container/heap interface;
+// a nodeQueue may be used as a priority queue.
+type nodeQueue []*graphNode
+
+func (a nodeQueue) Len() int { return len(a) }
+
+func (a nodeQueue) Swap(i, j int) {
+	x, y := a[i], a[j]
+	a[i], a[j] = y, x
+	x.index, y.index = j, i
+}
+
+func (a nodeQueue) Less(i, j int) bool {
+	x, y := a[i], a[j]
+	// nodes are prioritized by number of incoming dependencies (1st key)
+	// and source order (2nd key)
+	return x.ndeps < y.ndeps || x.ndeps == y.ndeps && x.obj.order() < y.obj.order()
+}
+
+func (a *nodeQueue) Push(x interface{}) {
+	panic("unreachable")
+}
+
+func (a *nodeQueue) Pop() interface{} {
+	n := len(*a)
+	x := (*a)[n-1]
+	x.index = -1 // for safety
+	*a = (*a)[:n-1]
+	return x
+}

third_party/forked/golang/go/types/labels.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// labels checks correct label use in body.
+func (check *Checker) labels(body *ast.BlockStmt) {
+	// set of all labels in this body
+	all := NewScope(nil, body.Pos(), body.End(), "label")
+
+	fwdJumps := check.blockBranches(all, nil, nil, body.List)
+
+	// If there are any forward jumps left, no label was found for
+	// the corresponding goto statements. Either those labels were
+	// never defined, or they are inside blocks and not reachable
+	// for the respective gotos.
+	for _, jmp := range fwdJumps {
+		var msg string
+		name := jmp.Label.Name
+		if alt := all.Lookup(name); alt != nil {
+			msg = "goto %s jumps into block"
+			alt.(*Label).used = true // avoid another error
+		} else {
+			msg = "label %s not declared"
+		}
+		check.errorf(jmp.Label.Pos(), msg, name)
+	}
+
+	// spec: "It is illegal to define a label that is never used."
+	for _, obj := range all.elems {
+		if lbl := obj.(*Label); !lbl.used {
+			check.softErrorf(lbl.pos, "label %s declared but not used", lbl.name)
+		}
+	}
+}
+
+// A block tracks label declarations in a block and its enclosing blocks.
+type block struct {
+	parent *block                      // enclosing block
+	lstmt  *ast.LabeledStmt            // labeled statement to which this block belongs, or nil
+	labels map[string]*ast.LabeledStmt // allocated lazily
+}
+
+// insert records a new label declaration for the current block.
+// The label must not have been declared before in any block.
+func (b *block) insert(s *ast.LabeledStmt) {
+	name := s.Label.Name
+	if debug {
+		assert(b.gotoTarget(name) == nil)
+	}
+	labels := b.labels
+	if labels == nil {
+		labels = make(map[string]*ast.LabeledStmt)
+		b.labels = labels
+	}
+	labels[name] = s
+}
+
+// gotoTarget returns the labeled statement in the current
+// or an enclosing block with the given label name, or nil.
+func (b *block) gotoTarget(name string) *ast.LabeledStmt {
+	for s := b; s != nil; s = s.parent {
+		if t := s.labels[name]; t != nil {
+			return t
+		}
+	}
+	return nil
+}
+
+// enclosingTarget returns the innermost enclosing labeled
+// statement with the given label name, or nil.
+func (b *block) enclosingTarget(name string) *ast.LabeledStmt {
+	for s := b; s != nil; s = s.parent {
+		if t := s.lstmt; t != nil && t.Label.Name == name {
+			return t
+		}
+	}
+	return nil
+}
+
+// blockBranches processes a block's statement list and returns the set of outgoing forward jumps.
+// all is the scope of all declared labels, parent the set of labels declared in the immediately
+// enclosing block, and lstmt is the labeled statement this block is associated with (or nil).
+func (check *Checker) blockBranches(all *Scope, parent *block, lstmt *ast.LabeledStmt, list []ast.Stmt) []*ast.BranchStmt {
+	b := &block{parent: parent, lstmt: lstmt}
+
+	var (
+		varDeclPos         token.Pos
+		fwdJumps, badJumps []*ast.BranchStmt
+	)
+
+	// All forward jumps jumping over a variable declaration are possibly
+	// invalid (they may still jump out of the block and be ok).
+	// recordVarDecl records them for the given position.
+	recordVarDecl := func(pos token.Pos) {
+		varDeclPos = pos
+		badJumps = append(badJumps[:0], fwdJumps...) // copy fwdJumps to badJumps
+	}
+
+	jumpsOverVarDecl := func(jmp *ast.BranchStmt) bool {
+		if varDeclPos.IsValid() {
+			for _, bad := range badJumps {
+				if jmp == bad {
+					return true
+				}
+			}
+		}
+		return false
+	}
+
+	blockBranches := func(lstmt *ast.LabeledStmt, list []ast.Stmt) {
+		// Unresolved forward jumps inside the nested block
+		// become forward jumps in the current block.
+		fwdJumps = append(fwdJumps, check.blockBranches(all, b, lstmt, list)...)
+	}
+
+	var stmtBranches func(ast.Stmt)
+	stmtBranches = func(s ast.Stmt) {
+		switch s := s.(type) {
+		case *ast.DeclStmt:
+			if d, _ := s.Decl.(*ast.GenDecl); d != nil && d.Tok == token.VAR {
+				recordVarDecl(d.Pos())
+			}
+
+		case *ast.LabeledStmt:
+			// declare non-blank label
+			if name := s.Label.Name; name != "_" {
+				lbl := NewLabel(s.Label.Pos(), check.pkg, name)
+				if alt := all.Insert(lbl); alt != nil {
+					check.softErrorf(lbl.pos, "label %s already declared", name)
+					check.reportAltDecl(alt)
+					// ok to continue
+				} else {
+					b.insert(s)
+					check.recordDef(s.Label, lbl)
+				}
+				// resolve matching forward jumps and remove them from fwdJumps
+				i := 0
+				for _, jmp := range fwdJumps {
+					if jmp.Label.Name == name {
+						// match
+						lbl.used = true
+						check.recordUse(jmp.Label, lbl)
+						if jumpsOverVarDecl(jmp) {
+							check.softErrorf(
+								jmp.Label.Pos(),
+								"goto %s jumps over variable declaration at line %d",
+								name,
+								check.fset.Position(varDeclPos).Line,
+							)
+							// ok to continue
+						}
+					} else {
+						// no match - record new forward jump
+						fwdJumps[i] = jmp
+						i++
+					}
+				}
+				fwdJumps = fwdJumps[:i]
+				lstmt = s
+			}
+			stmtBranches(s.Stmt)
+
+		case *ast.BranchStmt:
+			if s.Label == nil {
+				return // checked in 1st pass (check.stmt)
+			}
+
+			// determine and validate target
+			name := s.Label.Name
+			switch s.Tok {
+			case token.BREAK:
+				// spec: "If there is a label, it must be that of an enclosing
+				// "for", "switch", or "select" statement, and that is the one
+				// whose execution terminates."
+				valid := false
+				if t := b.enclosingTarget(name); t != nil {
+					switch t.Stmt.(type) {
+					case *ast.SwitchStmt, *ast.TypeSwitchStmt, *ast.SelectStmt, *ast.ForStmt, *ast.RangeStmt:
+						valid = true
+					}
+				}
+				if !valid {
+					check.errorf(s.Label.Pos(), "invalid break label %s", name)
+					return
+				}
+
+			case token.CONTINUE:
+				// spec: "If there is a label, it must be that of an enclosing
+				// "for" statement, and that is the one whose execution advances."
+				valid := false
+				if t := b.enclosingTarget(name); t != nil {
+					switch t.Stmt.(type) {
+					case *ast.ForStmt, *ast.RangeStmt:
+						valid = true
+					}
+				}
+				if !valid {
+					check.errorf(s.Label.Pos(), "invalid continue label %s", name)
+					return
+				}
+
+			case token.GOTO:
+				if b.gotoTarget(name) == nil {
+					// label may be declared later - add branch to forward jumps
+					fwdJumps = append(fwdJumps, s)
+					return
+				}
+
+			default:
+				check.invalidAST(s.Pos(), "branch statement: %s %s", s.Tok, name)
+				return
+			}
+
+			// record label use
+			obj := all.Lookup(name)
+			obj.(*Label).used = true
+			check.recordUse(s.Label, obj)
+
+		case *ast.AssignStmt:
+			if s.Tok == token.DEFINE {
+				recordVarDecl(s.Pos())
+			}
+
+		case *ast.BlockStmt:
+			blockBranches(lstmt, s.List)
+
+		case *ast.IfStmt:
+			stmtBranches(s.Body)
+			if s.Else != nil {
+				stmtBranches(s.Else)
+			}
+
+		case *ast.CaseClause:
+			blockBranches(nil, s.Body)
+
+		case *ast.SwitchStmt:
+			stmtBranches(s.Body)
+
+		case *ast.TypeSwitchStmt:
+			stmtBranches(s.Body)
+
+		case *ast.CommClause:
+			blockBranches(nil, s.Body)
+
+		case *ast.SelectStmt:
+			stmtBranches(s.Body)
+
+		case *ast.ForStmt:
+			stmtBranches(s.Body)
+
+		case *ast.RangeStmt:
+			stmtBranches(s.Body)
+		}
+	}
+
+	for _, s := range list {
+		stmtBranches(s)
+	}
+
+	return fwdJumps
+}

third_party/forked/golang/go/types/lookup.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements various field and method lookup functions.
+
+package types
+
+// LookupFieldOrMethod looks up a field or method with given package and name
+// in T and returns the corresponding *Var or *Func, an index sequence, and a
+// bool indicating if there were any pointer indirections on the path to the
+// field or method. If addressable is set, T is the type of an addressable
+// variable (only matters for method lookups).
+//
+// The last index entry is the field or method index in the (possibly embedded)
+// type where the entry was found, either:
+//
+//	1) the list of declared methods of a named type; or
+//	2) the list of all methods (method set) of an interface type; or
+//	3) the list of fields of a struct type.
+//
+// The earlier index entries are the indices of the anonymous struct fields
+// traversed to get to the found entry, starting at depth 0.
+//
+// If no entry is found, a nil object is returned. In this case, the returned
+// index and indirect values have the following meaning:
+//
+//	- If index != nil, the index sequence points to an ambiguous entry
+//	(the same name appeared more than once at the same embedding level).
+//
+//	- If indirect is set, a method with a pointer receiver type was found
+//      but there was no pointer on the path from the actual receiver type to
+//	the method's formal receiver base type, nor was the receiver addressable.
+//
+func LookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
+	// Methods cannot be associated to a named pointer type
+	// (spec: "The type denoted by T is called the receiver base type;
+	// it must not be a pointer or interface type and it must be declared
+	// in the same package as the method.").
+	// Thus, if we have a named pointer type, proceed with the underlying
+	// pointer type but discard the result if it is a method since we would
+	// not have found it for T (see also issue 8590).
+	if t, _ := T.(*Named); t != nil {
+		if p, _ := t.underlying.(*Pointer); p != nil {
+			obj, index, indirect = lookupFieldOrMethod(p, false, pkg, name)
+			if _, ok := obj.(*Func); ok {
+				return nil, nil, false
+			}
+			return
+		}
+	}
+
+	return lookupFieldOrMethod(T, addressable, pkg, name)
+}
+
+// TODO(gri) The named type consolidation and seen maps below must be
+//           indexed by unique keys for a given type. Verify that named
+//           types always have only one representation (even when imported
+//           indirectly via different packages.)
+
+func lookupFieldOrMethod(T Type, addressable bool, pkg *Package, name string) (obj Object, index []int, indirect bool) {
+	// WARNING: The code in this function is extremely subtle - do not modify casually!
+	//          This function and NewMethodSet should be kept in sync.
+
+	if name == "_" {
+		return // blank fields/methods are never found
+	}
+
+	typ, isPtr := deref(T)
+
+	// *typ where typ is an interface has no methods.
+	if isPtr && IsInterface(typ) {
+		return
+	}
+
+	// Start with typ as single entry at shallowest depth.
+	current := []embeddedType{{typ, nil, isPtr, false}}
+
+	// Named types that we have seen already, allocated lazily.
+	// Used to avoid endless searches in case of recursive types.
+	// Since only Named types can be used for recursive types, we
+	// only need to track those.
+	// (If we ever allow type aliases to construct recursive types,
+	// we must use type identity rather than pointer equality for
+	// the map key comparison, as we do in consolidateMultiples.)
+	var seen map[*Named]bool
+
+	// search current depth
+	for len(current) > 0 {
+		var next []embeddedType // embedded types found at current depth
+
+		// look for (pkg, name) in all types at current depth
+		for _, e := range current {
+			typ := e.typ
+
+			// If we have a named type, we may have associated methods.
+			// Look for those first.
+			if named, _ := typ.(*Named); named != nil {
+				if seen[named] {
+					// We have seen this type before, at a more shallow depth
+					// (note that multiples of this type at the current depth
+					// were consolidated before). The type at that depth shadows
+					// this same type at the current depth, so we can ignore
+					// this one.
+					continue
+				}
+				if seen == nil {
+					seen = make(map[*Named]bool)
+				}
+				seen[named] = true
+
+				// look for a matching attached method
+				if i, m := lookupMethod(named.methods, pkg, name); m != nil {
+					// potential match
+					assert(m.typ != nil)
+					index = concat(e.index, i)
+					if obj != nil || e.multiples {
+						return nil, index, false // collision
+					}
+					obj = m
+					indirect = e.indirect
+					continue // we can't have a matching field or interface method
+				}
+
+				// continue with underlying type
+				typ = named.underlying
+			}
+
+			switch t := typ.(type) {
+			case *Struct:
+				// look for a matching field and collect embedded types
+				for i, f := range t.fields {
+					if f.sameId(pkg, name) {
+						assert(f.typ != nil)
+						index = concat(e.index, i)
+						if obj != nil || e.multiples {
+							return nil, index, false // collision
+						}
+						obj = f
+						indirect = e.indirect
+						continue // we can't have a matching interface method
+					}
+					// Collect embedded struct fields for searching the next
+					// lower depth, but only if we have not seen a match yet
+					// (if we have a match it is either the desired field or
+					// we have a name collision on the same depth; in either
+					// case we don't need to look further).
+					// Embedded fields are always of the form T or *T where
+					// T is a type name. If e.typ appeared multiple times at
+					// this depth, f.typ appears multiple times at the next
+					// depth.
+					if obj == nil && f.anonymous {
+						typ, isPtr := deref(f.typ)
+						// TODO(gri) optimization: ignore types that can't
+						// have fields or methods (only Named, Struct, and
+						// Interface types need to be considered).
+						next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
+					}
+				}
+
+			case *Interface:
+				// look for a matching method
+				// TODO(gri) t.allMethods is sorted - use binary search
+				if i, m := lookupMethod(t.allMethods, pkg, name); m != nil {
+					assert(m.typ != nil)
+					index = concat(e.index, i)
+					if obj != nil || e.multiples {
+						return nil, index, false // collision
+					}
+					obj = m
+					indirect = e.indirect
+				}
+			}
+		}
+
+		if obj != nil {
+			// found a potential match
+			// spec: "A method call x.m() is valid if the method set of (the type of) x
+			//        contains m and the argument list can be assigned to the parameter
+			//        list of m. If x is addressable and &x's method set contains m, x.m()
+			//        is shorthand for (&x).m()".
+			if f, _ := obj.(*Func); f != nil && ptrRecv(f) && !indirect && !addressable {
+				return nil, nil, true // pointer/addressable receiver required
+			}
+			return
+		}
+
+		current = consolidateMultiples(next)
+	}
+
+	return nil, nil, false // not found
+}
+
+// embeddedType represents an embedded type
+type embeddedType struct {
+	typ       Type
+	index     []int // embedded field indices, starting with index at depth 0
+	indirect  bool  // if set, there was a pointer indirection on the path to this field
+	multiples bool  // if set, typ appears multiple times at this depth
+}
+
+// consolidateMultiples collects multiple list entries with the same type
+// into a single entry marked as containing multiples. The result is the
+// consolidated list.
+func consolidateMultiples(list []embeddedType) []embeddedType {
+	if len(list) <= 1 {
+		return list // at most one entry - nothing to do
+	}
+
+	n := 0                     // number of entries w/ unique type
+	prev := make(map[Type]int) // index at which type was previously seen
+	for _, e := range list {
+		if i, found := lookupType(prev, e.typ); found {
+			list[i].multiples = true
+			// ignore this entry
+		} else {
+			prev[e.typ] = n
+			list[n] = e
+			n++
+		}
+	}
+	return list[:n]
+}
+
+func lookupType(m map[Type]int, typ Type) (int, bool) {
+	// fast path: maybe the types are equal
+	if i, found := m[typ]; found {
+		return i, true
+	}
+
+	for t, i := range m {
+		if Identical(t, typ) {
+			return i, true
+		}
+	}
+
+	return 0, false
+}
+
+// MissingMethod returns (nil, false) if V implements T, otherwise it
+// returns a missing method required by T and whether it is missing or
+// just has the wrong type.
+//
+// For non-interface types V, or if static is set, V implements T if all
+// methods of T are present in V. Otherwise (V is an interface and static
+// is not set), MissingMethod only checks that methods of T which are also
+// present in V have matching types (e.g., for a type assertion x.(T) where
+// x is of interface type V).
+//
+func MissingMethod(V Type, T *Interface, static bool) (method *Func, wrongType bool) {
+	// fast path for common case
+	if T.Empty() {
+		return
+	}
+
+	// TODO(gri) Consider using method sets here. Might be more efficient.
+
+	if ityp, _ := V.Underlying().(*Interface); ityp != nil {
+		// TODO(gri) allMethods is sorted - can do this more efficiently
+		for _, m := range T.allMethods {
+			_, obj := lookupMethod(ityp.allMethods, m.pkg, m.name)
+			switch {
+			case obj == nil:
+				if static {
+					return m, false
+				}
+			case !Identical(obj.Type(), m.typ):
+				return m, true
+			}
+		}
+		return
+	}
+
+	// A concrete type implements T if it implements all methods of T.
+	for _, m := range T.allMethods {
+		obj, _, _ := lookupFieldOrMethod(V, false, m.pkg, m.name)
+
+		f, _ := obj.(*Func)
+		if f == nil {
+			return m, false
+		}
+
+		if !Identical(f.typ, m.typ) {
+			return m, true
+		}
+	}
+
+	return
+}
+
+// assertableTo reports whether a value of type V can be asserted to have type T.
+// It returns (nil, false) as affirmative answer. Otherwise it returns a missing
+// method required by V and whether it is missing or just has the wrong type.
+func assertableTo(V *Interface, T Type) (method *Func, wrongType bool) {
+	// no static check is required if T is an interface
+	// spec: "If T is an interface type, x.(T) asserts that the
+	//        dynamic type of x implements the interface T."
+	if _, ok := T.Underlying().(*Interface); ok && !strict {
+		return
+	}
+	return MissingMethod(T, V, false)
+}
+
+// deref dereferences typ if it is a *Pointer and returns its base and true.
+// Otherwise it returns (typ, false).
+func deref(typ Type) (Type, bool) {
+	if p, _ := typ.(*Pointer); p != nil {
+		return p.base, true
+	}
+	return typ, false
+}
+
+// derefStructPtr dereferences typ if it is a (named or unnamed) pointer to a
+// (named or unnamed) struct and returns its base. Otherwise it returns typ.
+func derefStructPtr(typ Type) Type {
+	if p, _ := typ.Underlying().(*Pointer); p != nil {
+		if _, ok := p.base.Underlying().(*Struct); ok {
+			return p.base
+		}
+	}
+	return typ
+}
+
+// concat returns the result of concatenating list and i.
+// The result does not share its underlying array with list.
+func concat(list []int, i int) []int {
+	var t []int
+	t = append(t, list...)
+	return append(t, i)
+}
+
+// fieldIndex returns the index for the field with matching package and name, or a value < 0.
+func fieldIndex(fields []*Var, pkg *Package, name string) int {
+	if name != "_" {
+		for i, f := range fields {
+			if f.sameId(pkg, name) {
+				return i
+			}
+		}
+	}
+	return -1
+}
+
+// lookupMethod returns the index of and method with matching package and name, or (-1, nil).
+func lookupMethod(methods []*Func, pkg *Package, name string) (int, *Func) {
+	if name != "_" {
+		for i, m := range methods {
+			if m.sameId(pkg, name) {
+				return i, m
+			}
+		}
+	}
+	return -1, nil
+}

third_party/forked/golang/go/types/methodset.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements method sets.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"sort"
+)
+
+// A MethodSet is an ordered set of concrete or abstract (interface) methods;
+// a method is a MethodVal selection, and they are ordered by ascending m.Obj().Id().
+// The zero value for a MethodSet is a ready-to-use empty method set.
+type MethodSet struct {
+	list []*Selection
+}
+
+func (s *MethodSet) String() string {
+	if s.Len() == 0 {
+		return "MethodSet {}"
+	}
+
+	var buf bytes.Buffer
+	fmt.Fprintln(&buf, "MethodSet {")
+	for _, f := range s.list {
+		fmt.Fprintf(&buf, "\t%s\n", f)
+	}
+	fmt.Fprintln(&buf, "}")
+	return buf.String()
+}
+
+// Len returns the number of methods in s.
+func (s *MethodSet) Len() int { return len(s.list) }
+
+// At returns the i'th method in s for 0 <= i < s.Len().
+func (s *MethodSet) At(i int) *Selection { return s.list[i] }
+
+// Lookup returns the method with matching package and name, or nil if not found.
+func (s *MethodSet) Lookup(pkg *Package, name string) *Selection {
+	if s.Len() == 0 {
+		return nil
+	}
+
+	key := Id(pkg, name)
+	i := sort.Search(len(s.list), func(i int) bool {
+		m := s.list[i]
+		return m.obj.Id() >= key
+	})
+	if i < len(s.list) {
+		m := s.list[i]
+		if m.obj.Id() == key {
+			return m
+		}
+	}
+	return nil
+}
+
+// Shared empty method set.
+var emptyMethodSet MethodSet
+
+// NewMethodSet returns the method set for the given type T.
+// It always returns a non-nil method set, even if it is empty.
+func NewMethodSet(T Type) *MethodSet {
+	// WARNING: The code in this function is extremely subtle - do not modify casually!
+	//          This function and lookupFieldOrMethod should be kept in sync.
+
+	// method set up to the current depth, allocated lazily
+	var base methodSet
+
+	typ, isPtr := deref(T)
+
+	// *typ where typ is an interface has no methods.
+	if isPtr && IsInterface(typ) {
+		return &emptyMethodSet
+	}
+
+	// Start with typ as single entry at shallowest depth.
+	current := []embeddedType{{typ, nil, isPtr, false}}
+
+	// Named types that we have seen already, allocated lazily.
+	// Used to avoid endless searches in case of recursive types.
+	// Since only Named types can be used for recursive types, we
+	// only need to track those.
+	// (If we ever allow type aliases to construct recursive types,
+	// we must use type identity rather than pointer equality for
+	// the map key comparison, as we do in consolidateMultiples.)
+	var seen map[*Named]bool
+
+	// collect methods at current depth
+	for len(current) > 0 {
+		var next []embeddedType // embedded types found at current depth
+
+		// field and method sets at current depth, allocated lazily
+		var fset fieldSet
+		var mset methodSet
+
+		for _, e := range current {
+			typ := e.typ
+
+			// If we have a named type, we may have associated methods.
+			// Look for those first.
+			if named, _ := typ.(*Named); named != nil {
+				if seen[named] {
+					// We have seen this type before, at a more shallow depth
+					// (note that multiples of this type at the current depth
+					// were consolidated before). The type at that depth shadows
+					// this same type at the current depth, so we can ignore
+					// this one.
+					continue
+				}
+				if seen == nil {
+					seen = make(map[*Named]bool)
+				}
+				seen[named] = true
+
+				mset = mset.add(named.methods, e.index, e.indirect, e.multiples)
+
+				// continue with underlying type
+				typ = named.underlying
+			}
+
+			switch t := typ.(type) {
+			case *Struct:
+				for i, f := range t.fields {
+					fset = fset.add(f, e.multiples)
+
+					// Embedded fields are always of the form T or *T where
+					// T is a type name. If typ appeared multiple times at
+					// this depth, f.Type appears multiple times at the next
+					// depth.
+					if f.anonymous {
+						typ, isPtr := deref(f.typ)
+						// TODO(gri) optimization: ignore types that can't
+						// have fields or methods (only Named, Struct, and
+						// Interface types need to be considered).
+						next = append(next, embeddedType{typ, concat(e.index, i), e.indirect || isPtr, e.multiples})
+					}
+				}
+
+			case *Interface:
+				mset = mset.add(t.allMethods, e.index, true, e.multiples)
+			}
+		}
+
+		// Add methods and collisions at this depth to base if no entries with matching
+		// names exist already.
+		for k, m := range mset {
+			if _, found := base[k]; !found {
+				// Fields collide with methods of the same name at this depth.
+				if _, found := fset[k]; found {
+					m = nil // collision
+				}
+				if base == nil {
+					base = make(methodSet)
+				}
+				base[k] = m
+			}
+		}
+
+		// Multiple fields with matching names collide at this depth and shadow all
+		// entries further down; add them as collisions to base if no entries with
+		// matching names exist already.
+		for k, f := range fset {
+			if f == nil {
+				if _, found := base[k]; !found {
+					if base == nil {
+						base = make(methodSet)
+					}
+					base[k] = nil // collision
+				}
+			}
+		}
+
+		current = consolidateMultiples(next)
+	}
+
+	if len(base) == 0 {
+		return &emptyMethodSet
+	}
+
+	// collect methods
+	var list []*Selection
+	for _, m := range base {
+		if m != nil {
+			m.recv = T
+			list = append(list, m)
+		}
+	}
+	// sort by unique name
+	sort.Slice(list, func(i, j int) bool {
+		return list[i].obj.Id() < list[j].obj.Id()
+	})
+	return &MethodSet{list}
+}
+
+// A fieldSet is a set of fields and name collisions.
+// A collision indicates that multiple fields with the
+// same unique id appeared.
+type fieldSet map[string]*Var // a nil entry indicates a name collision
+
+// Add adds field f to the field set s.
+// If multiples is set, f appears multiple times
+// and is treated as a collision.
+func (s fieldSet) add(f *Var, multiples bool) fieldSet {
+	if s == nil {
+		s = make(fieldSet)
+	}
+	key := f.Id()
+	// if f is not in the set, add it
+	if !multiples {
+		if _, found := s[key]; !found {
+			s[key] = f
+			return s
+		}
+	}
+	s[key] = nil // collision
+	return s
+}
+
+// A methodSet is a set of methods and name collisions.
+// A collision indicates that multiple methods with the
+// same unique id appeared.
+type methodSet map[string]*Selection // a nil entry indicates a name collision
+
+// Add adds all functions in list to the method set s.
+// If multiples is set, every function in list appears multiple times
+// and is treated as a collision.
+func (s methodSet) add(list []*Func, index []int, indirect bool, multiples bool) methodSet {
+	if len(list) == 0 {
+		return s
+	}
+	if s == nil {
+		s = make(methodSet)
+	}
+	for i, f := range list {
+		key := f.Id()
+		// if f is not in the set, add it
+		if !multiples {
+			// TODO(gri) A found method may not be added because it's not in the method set
+			// (!indirect && ptrRecv(f)). A 2nd method on the same level may be in the method
+			// set and may not collide with the first one, thus leading to a false positive.
+			// Is that possible? Investigate.
+			if _, found := s[key]; !found && (indirect || !ptrRecv(f)) {
+				s[key] = &Selection{MethodVal, nil, f, concat(index, i), indirect}
+				continue
+			}
+		}
+		s[key] = nil // collision
+	}
+	return s
+}
+
+// ptrRecv reports whether the receiver is of the form *T.
+// The receiver must exist.
+func ptrRecv(f *Func) bool {
+	_, isPtr := deref(f.typ.(*Signature).recv.typ)
+	return isPtr
+}

third_party/forked/golang/go/types/object.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+// An Object describes a named language entity such as a package,
+// constant, type, variable, function (incl. methods), or label.
+// All objects implement the Object interface.
+//
+type Object interface {
+	Parent() *Scope // scope in which this object is declared; nil for methods and struct fields
+	Pos() token.Pos // position of object identifier in declaration
+	Pkg() *Package  // package to which this object belongs; nil for labels and objects in the Universe scope
+	Name() string   // package local object name
+	Type() Type     // object type
+	Exported() bool // reports whether the name starts with a capital letter
+	Id() string     // object name if exported, qualified name if not exported (see func Id)
+
+	// String returns a human-readable string of the object.
+	String() string
+
+	// order reflects a package-level object's source order: if object
+	// a is before object b in the source, then a.order() < b.order().
+	// order returns a value > 0 for package-level objects; it returns
+	// 0 for all other objects (including objects in file scopes).
+	order() uint32
+
+	// setOrder sets the order number of the object. It must be > 0.
+	setOrder(uint32)
+
+	// setParent sets the parent scope of the object.
+	setParent(*Scope)
+
+	// sameId reports whether obj.Id() and Id(pkg, name) are the same.
+	sameId(pkg *Package, name string) bool
+
+	// scopePos returns the start position of the scope of this Object
+	scopePos() token.Pos
+
+	// setScopePos sets the start position of the scope for this Object.
+	setScopePos(pos token.Pos)
+}
+
+// Id returns name if it is exported, otherwise it
+// returns the name qualified with the package path.
+func Id(pkg *Package, name string) string {
+	if ast.IsExported(name) {
+		return name
+	}
+	// unexported names need the package path for differentiation
+	// (if there's no package, make sure we don't start with '.'
+	// as that may change the order of methods between a setup
+	// inside a package and outside a package - which breaks some
+	// tests)
+	path := "_"
+	// pkg is nil for objects in Universe scope and possibly types
+	// introduced via Eval (see also comment in object.sameId)
+	if pkg != nil && pkg.path != "" {
+		path = pkg.path
+	}
+	return path + "." + name
+}
+
+// An object implements the common parts of an Object.
+type object struct {
+	parent    *Scope
+	pos       token.Pos
+	pkg       *Package
+	name      string
+	typ       Type
+	order_    uint32
+	scopePos_ token.Pos
+}
+
+func (obj *object) Parent() *Scope      { return obj.parent }
+func (obj *object) Pos() token.Pos      { return obj.pos }
+func (obj *object) Pkg() *Package       { return obj.pkg }
+func (obj *object) Name() string        { return obj.name }
+func (obj *object) Type() Type          { return obj.typ }
+func (obj *object) Exported() bool      { return ast.IsExported(obj.name) }
+func (obj *object) Id() string          { return Id(obj.pkg, obj.name) }
+func (obj *object) String() string      { panic("abstract") }
+func (obj *object) order() uint32       { return obj.order_ }
+func (obj *object) scopePos() token.Pos { return obj.scopePos_ }
+
+func (obj *object) setParent(parent *Scope)   { obj.parent = parent }
+func (obj *object) setOrder(order uint32)     { assert(order > 0); obj.order_ = order }
+func (obj *object) setScopePos(pos token.Pos) { obj.scopePos_ = pos }
+
+func (obj *object) sameId(pkg *Package, name string) bool {
+	// spec:
+	// "Two identifiers are different if they are spelled differently,
+	// or if they appear in different packages and are not exported.
+	// Otherwise, they are the same."
+	if name != obj.name {
+		return false
+	}
+	// obj.Name == name
+	if obj.Exported() {
+		return true
+	}
+	// not exported, so packages must be the same (pkg == nil for
+	// fields in Universe scope; this can only happen for types
+	// introduced via Eval)
+	if pkg == nil || obj.pkg == nil {
+		return pkg == obj.pkg
+	}
+	// pkg != nil && obj.pkg != nil
+	return pkg.path == obj.pkg.path
+}
+
+// A PkgName represents an imported Go package.
+// PkgNames don't have a type.
+type PkgName struct {
+	object
+	imported *Package
+	used     bool // set if the package was used
+}
+
+// NewPkgName returns a new PkgName object representing an imported package.
+// The remaining arguments set the attributes found with all Objects.
+func NewPkgName(pos token.Pos, pkg *Package, name string, imported *Package) *PkgName {
+	return &PkgName{object{nil, pos, pkg, name, Typ[Invalid], 0, token.NoPos}, imported, false}
+}
+
+// Imported returns the package that was imported.
+// It is distinct from Pkg(), which is the package containing the import statement.
+func (obj *PkgName) Imported() *Package { return obj.imported }
+
+// A Const represents a declared constant.
+type Const struct {
+	object
+	val     constant.Value
+	visited bool // for initialization cycle detection
+}
+
+// NewConst returns a new constant with value val.
+// The remaining arguments set the attributes found with all Objects.
+func NewConst(pos token.Pos, pkg *Package, name string, typ Type, val constant.Value) *Const {
+	return &Const{object{nil, pos, pkg, name, typ, 0, token.NoPos}, val, false}
+}
+
+func (obj *Const) Val() constant.Value { return obj.val }
+func (*Const) isDependency()           {} // a constant may be a dependency of an initialization expression
+
+// A TypeName represents a name for a (named or alias) type.
+type TypeName struct {
+	object
+}
+
+// NewTypeName returns a new type name denoting the given typ.
+// The remaining arguments set the attributes found with all Objects.
+//
+// The typ argument may be a defined (Named) type or an alias type.
+// It may also be nil such that the returned TypeName can be used as
+// argument for NewNamed, which will set the TypeName's type as a side-
+// effect.
+func NewTypeName(pos token.Pos, pkg *Package, name string, typ Type) *TypeName {
+	return &TypeName{object{nil, pos, pkg, name, typ, 0, token.NoPos}}
+}
+
+// IsAlias reports whether obj is an alias name for a type.
+func (obj *TypeName) IsAlias() bool {
+	switch t := obj.typ.(type) {
+	case nil:
+		return false
+	case *Basic:
+		// unsafe.Pointer is not an alias.
+		if obj.pkg == Unsafe {
+			return false
+		}
+		// Any user-defined type name for a basic type is an alias for a
+		// basic type (because basic types are pre-declared in the Universe
+		// scope, outside any package scope), and so is any type name with
+		// a different name than the name of the basic type it refers to.
+		// Additionally, we need to look for "byte" and "rune" because they
+		// are aliases but have the same names (for better error messages).
+		return obj.pkg != nil || t.name != obj.name || t == universeByte || t == universeRune
+	case *Named:
+		return obj != t.obj
+	default:
+		return true
+	}
+}
+
+// A Variable represents a declared variable (including function parameters and results, and struct fields).
+type Var struct {
+	object
+	anonymous bool // if set, the variable is an anonymous struct field, and name is the type name
+	visited   bool // for initialization cycle detection
+	isField   bool // var is struct field
+	used      bool // set if the variable was used
+}
+
+// NewVar returns a new variable.
+// The arguments set the attributes found with all Objects.
+func NewVar(pos token.Pos, pkg *Package, name string, typ Type) *Var {
+	return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}}
+}
+
+// NewParam returns a new variable representing a function parameter.
+func NewParam(pos token.Pos, pkg *Package, name string, typ Type) *Var {
+	return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}, used: true} // parameters are always 'used'
+}
+
+// NewField returns a new variable representing a struct field.
+// For anonymous (embedded) fields, the name is the unqualified
+// type name under which the field is accessible.
+func NewField(pos token.Pos, pkg *Package, name string, typ Type, anonymous bool) *Var {
+	return &Var{object: object{nil, pos, pkg, name, typ, 0, token.NoPos}, anonymous: anonymous, isField: true}
+}
+
+// Anonymous reports whether the variable is an anonymous field.
+func (obj *Var) Anonymous() bool { return obj.anonymous }
+
+// IsField reports whether the variable is a struct field.
+func (obj *Var) IsField() bool { return obj.isField }
+
+func (*Var) isDependency() {} // a variable may be a dependency of an initialization expression
+
+// A Func represents a declared function, concrete method, or abstract
+// (interface) method. Its Type() is always a *Signature.
+// An abstract method may belong to many interfaces due to embedding.
+type Func struct {
+	object
+}
+
+// NewFunc returns a new function with the given signature, representing
+// the function's type.
+func NewFunc(pos token.Pos, pkg *Package, name string, sig *Signature) *Func {
+	// don't store a nil signature
+	var typ Type
+	if sig != nil {
+		typ = sig
+	}
+	return &Func{object{nil, pos, pkg, name, typ, 0, token.NoPos}}
+}
+
+// FullName returns the package- or receiver-type-qualified name of
+// function or method obj.
+func (obj *Func) FullName() string {
+	var buf bytes.Buffer
+	writeFuncName(&buf, obj, nil)
+	return buf.String()
+}
+
+// Scope returns the scope of the function's body block.
+func (obj *Func) Scope() *Scope { return obj.typ.(*Signature).scope }
+
+func (*Func) isDependency() {} // a function may be a dependency of an initialization expression
+
+// A Label represents a declared label.
+// Labels don't have a type.
+type Label struct {
+	object
+	used bool // set if the label was used
+}
+
+// NewLabel returns a new label.
+func NewLabel(pos token.Pos, pkg *Package, name string) *Label {
+	return &Label{object{pos: pos, pkg: pkg, name: name, typ: Typ[Invalid]}, false}
+}
+
+// A Builtin represents a built-in function.
+// Builtins don't have a valid type.
+type Builtin struct {
+	object
+	id builtinId
+}
+
+func newBuiltin(id builtinId) *Builtin {
+	return &Builtin{object{name: predeclaredFuncs[id].name, typ: Typ[Invalid]}, id}
+}
+
+// Nil represents the predeclared value nil.
+type Nil struct {
+	object
+}
+
+func writeObject(buf *bytes.Buffer, obj Object, qf Qualifier) {
+	var tname *TypeName
+	typ := obj.Type()
+
+	switch obj := obj.(type) {
+	case *PkgName:
+		fmt.Fprintf(buf, "package %s", obj.Name())
+		if path := obj.imported.path; path != "" && path != obj.name {
+			fmt.Fprintf(buf, " (%q)", path)
+		}
+		return
+
+	case *Const:
+		buf.WriteString("const")
+
+	case *TypeName:
+		tname = obj
+		buf.WriteString("type")
+
+	case *Var:
+		if obj.isField {
+			buf.WriteString("field")
+		} else {
+			buf.WriteString("var")
+		}
+
+	case *Func:
+		buf.WriteString("func ")
+		writeFuncName(buf, obj, qf)
+		if typ != nil {
+			WriteSignature(buf, typ.(*Signature), qf)
+		}
+		return
+
+	case *Label:
+		buf.WriteString("label")
+		typ = nil
+
+	case *Builtin:
+		buf.WriteString("builtin")
+		typ = nil
+
+	case *Nil:
+		buf.WriteString("nil")
+		return
+
+	default:
+		panic(fmt.Sprintf("writeObject(%T)", obj))
+	}
+
+	buf.WriteByte(' ')
+
+	// For package-level objects, qualify the name.
+	if obj.Pkg() != nil && obj.Pkg().scope.Lookup(obj.Name()) == obj {
+		writePackage(buf, obj.Pkg(), qf)
+	}
+	buf.WriteString(obj.Name())
+
+	if typ == nil {
+		return
+	}
+
+	if tname != nil {
+		// We have a type object: Don't print anything more for
+		// basic types since there's no more information (names
+		// are the same; see also comment in TypeName.IsAlias).
+		if _, ok := typ.(*Basic); ok {
+			return
+		}
+		if tname.IsAlias() {
+			buf.WriteString(" =")
+		} else {
+			typ = typ.Underlying()
+		}
+	}
+
+	buf.WriteByte(' ')
+	WriteType(buf, typ, qf)
+}
+
+func writePackage(buf *bytes.Buffer, pkg *Package, qf Qualifier) {
+	if pkg == nil {
+		return
+	}
+	var s string
+	if qf != nil {
+		s = qf(pkg)
+	} else {
+		s = pkg.Path()
+	}
+	if s != "" {
+		buf.WriteString(s)
+		buf.WriteByte('.')
+	}
+}
+
+// ObjectString returns the string form of obj.
+// The Qualifier controls the printing of
+// package-level objects, and may be nil.
+func ObjectString(obj Object, qf Qualifier) string {
+	var buf bytes.Buffer
+	writeObject(&buf, obj, qf)
+	return buf.String()
+}
+
+func (obj *PkgName) String() string  { return ObjectString(obj, nil) }
+func (obj *Const) String() string    { return ObjectString(obj, nil) }
+func (obj *TypeName) String() string { return ObjectString(obj, nil) }
+func (obj *Var) String() string      { return ObjectString(obj, nil) }
+func (obj *Func) String() string     { return ObjectString(obj, nil) }
+func (obj *Label) String() string    { return ObjectString(obj, nil) }
+func (obj *Builtin) String() string  { return ObjectString(obj, nil) }
+func (obj *Nil) String() string      { return ObjectString(obj, nil) }
+
+func writeFuncName(buf *bytes.Buffer, f *Func, qf Qualifier) {
+	if f.typ != nil {
+		sig := f.typ.(*Signature)
+		if recv := sig.Recv(); recv != nil {
+			buf.WriteByte('(')
+			if _, ok := recv.Type().(*Interface); ok {
+				// gcimporter creates abstract methods of
+				// named interfaces using the interface type
+				// (not the named type) as the receiver.
+				// Don't print it in full.
+				buf.WriteString("interface")
+			} else {
+				WriteType(buf, recv.Type(), qf)
+			}
+			buf.WriteByte(')')
+			buf.WriteByte('.')
+		} else if f.pkg != nil {
+			writePackage(buf, f.pkg, qf)
+		}
+	}
+	buf.WriteString(f.name)
+}

third_party/forked/golang/go/types/objset.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements objsets.
+//
+// An objset is similar to a Scope but objset elements
+// are identified by their unique id, instead of their
+// object name.
+
+package types
+
+// An objset is a set of objects identified by their unique id.
+// The zero value for objset is a ready-to-use empty objset.
+type objset map[string]Object // initialized lazily
+
+// insert attempts to insert an object obj into objset s.
+// If s already contains an alternative object alt with
+// the same name, insert leaves s unchanged and returns alt.
+// Otherwise it inserts obj and returns nil.
+func (s *objset) insert(obj Object) Object {
+	id := obj.Id()
+	if alt := (*s)[id]; alt != nil {
+		return alt
+	}
+	if *s == nil {
+		*s = make(map[string]Object)
+	}
+	(*s)[id] = obj
+	return nil
+}

third_party/forked/golang/go/types/operand.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file defines operands and associated operations.
+
+package types
+
+import (
+	"bytes"
+	"go/ast"
+	"go/constant"
+	"go/token"
+)
+
+// An operandMode specifies the (addressing) mode of an operand.
+type operandMode byte
+
+const (
+	invalid   operandMode = iota // operand is invalid
+	novalue                      // operand represents no value (result of a function call w/o result)
+	builtin                      // operand is a built-in function
+	typexpr                      // operand is a type
+	constant_                    // operand is a constant; the operand's typ is a Basic type
+	variable                     // operand is an addressable variable
+	mapindex                     // operand is a map index expression (acts like a variable on lhs, commaok on rhs of an assignment)
+	value                        // operand is a computed value
+	commaok                      // like value, but operand may be used in a comma,ok expression
+)
+
+var operandModeString = [...]string{
+	invalid:   "invalid operand",
+	novalue:   "no value",
+	builtin:   "built-in",
+	typexpr:   "type",
+	constant_: "constant",
+	variable:  "variable",
+	mapindex:  "map index expression",
+	value:     "value",
+	commaok:   "comma, ok expression",
+}
+
+// An operand represents an intermediate value during type checking.
+// Operands have an (addressing) mode, the expression evaluating to
+// the operand, the operand's type, a value for constants, and an id
+// for built-in functions.
+// The zero value of operand is a ready to use invalid operand.
+//
+type operand struct {
+	mode operandMode
+	expr ast.Expr
+	typ  Type
+	val  constant.Value
+	id   builtinId
+}
+
+// pos returns the position of the expression corresponding to x.
+// If x is invalid the position is token.NoPos.
+//
+func (x *operand) pos() token.Pos {
+	// x.expr may not be set if x is invalid
+	if x.expr == nil {
+		return token.NoPos
+	}
+	return x.expr.Pos()
+}
+
+// Operand string formats
+// (not all "untyped" cases can appear due to the type system,
+// but they fall out naturally here)
+//
+// mode       format
+//
+// invalid    <expr> (               <mode>                    )
+// novalue    <expr> (               <mode>                    )
+// builtin    <expr> (               <mode>                    )
+// typexpr    <expr> (               <mode>                    )
+//
+// constant   <expr> (<untyped kind> <mode>                    )
+// constant   <expr> (               <mode>       of type <typ>)
+// constant   <expr> (<untyped kind> <mode> <val>              )
+// constant   <expr> (               <mode> <val> of type <typ>)
+//
+// variable   <expr> (<untyped kind> <mode>                    )
+// variable   <expr> (               <mode>       of type <typ>)
+//
+// mapindex   <expr> (<untyped kind> <mode>                    )
+// mapindex   <expr> (               <mode>       of type <typ>)
+//
+// value      <expr> (<untyped kind> <mode>                    )
+// value      <expr> (               <mode>       of type <typ>)
+//
+// commaok    <expr> (<untyped kind> <mode>                    )
+// commaok    <expr> (               <mode>       of type <typ>)
+//
+func operandString(x *operand, qf Qualifier) string {
+	var buf bytes.Buffer
+
+	var expr string
+	if x.expr != nil {
+		expr = ExprString(x.expr)
+	} else {
+		switch x.mode {
+		case builtin:
+			expr = predeclaredFuncs[x.id].name
+		case typexpr:
+			expr = TypeString(x.typ, qf)
+		case constant_:
+			expr = x.val.String()
+		}
+	}
+
+	// <expr> (
+	if expr != "" {
+		buf.WriteString(expr)
+		buf.WriteString(" (")
+	}
+
+	// <untyped kind>
+	hasType := false
+	switch x.mode {
+	case invalid, novalue, builtin, typexpr:
+		// no type
+	default:
+		// should have a type, but be cautious (don't crash during printing)
+		if x.typ != nil {
+			if isUntyped(x.typ) {
+				buf.WriteString(x.typ.(*Basic).name)
+				buf.WriteByte(' ')
+				break
+			}
+			hasType = true
+		}
+	}
+
+	// <mode>
+	buf.WriteString(operandModeString[x.mode])
+
+	// <val>
+	if x.mode == constant_ {
+		if s := x.val.String(); s != expr {
+			buf.WriteByte(' ')
+			buf.WriteString(s)
+		}
+	}
+
+	// <typ>
+	if hasType {
+		if x.typ != Typ[Invalid] {
+			buf.WriteString(" of type ")
+			WriteType(&buf, x.typ, qf)
+		} else {
+			buf.WriteString(" with invalid type")
+		}
+	}
+
+	// )
+	if expr != "" {
+		buf.WriteByte(')')
+	}
+
+	return buf.String()
+}
+
+func (x *operand) String() string {
+	return operandString(x, nil)
+}
+
+// setConst sets x to the untyped constant for literal lit.
+func (x *operand) setConst(tok token.Token, lit string) {
+	var kind BasicKind
+	switch tok {
+	case token.INT:
+		kind = UntypedInt
+	case token.FLOAT:
+		kind = UntypedFloat
+	case token.IMAG:
+		kind = UntypedComplex
+	case token.CHAR:
+		kind = UntypedRune
+	case token.STRING:
+		kind = UntypedString
+	default:
+		unreachable()
+	}
+
+	x.mode = constant_
+	x.typ = Typ[kind]
+	x.val = constant.MakeFromLiteral(lit, tok, 0)
+}
+
+// isNil reports whether x is the nil value.
+func (x *operand) isNil() bool {
+	return x.mode == value && x.typ == Typ[UntypedNil]
+}
+
+// TODO(gri) The functions operand.assignableTo, checker.convertUntyped,
+//           checker.representable, and checker.assignment are
+//           overlapping in functionality. Need to simplify and clean up.
+
+// assignableTo reports whether x is assignable to a variable of type T.
+// If the result is false and a non-nil reason is provided, it may be set
+// to a more detailed explanation of the failure (result != "").
+func (x *operand) assignableTo(conf *Config, T Type, reason *string) bool {
+	if x.mode == invalid || T == Typ[Invalid] {
+		return true // avoid spurious errors
+	}
+
+	V := x.typ
+
+	// x's type is identical to T
+	if Identical(V, T) {
+		return true
+	}
+
+	Vu := V.Underlying()
+	Tu := T.Underlying()
+
+	// x is an untyped value representable by a value of type T
+	// TODO(gri) This is borrowing from checker.convertUntyped and
+	//           checker.representable. Need to clean up.
+	if isUntyped(Vu) {
+		switch t := Tu.(type) {
+		case *Basic:
+			if x.isNil() && t.kind == UnsafePointer {
+				return true
+			}
+			if x.mode == constant_ {
+				return representableConst(x.val, conf, t, nil)
+			}
+			// The result of a comparison is an untyped boolean,
+			// but may not be a constant.
+			if Vb, _ := Vu.(*Basic); Vb != nil {
+				return Vb.kind == UntypedBool && isBoolean(Tu)
+			}
+		case *Interface:
+			return x.isNil() || t.Empty()
+		case *Pointer, *Signature, *Slice, *Map, *Chan:
+			return x.isNil()
+		}
+	}
+	// Vu is typed
+
+	// x's type V and T have identical underlying types
+	// and at least one of V or T is not a named type
+	if Identical(Vu, Tu) && (!isNamed(V) || !isNamed(T)) {
+		return true
+	}
+
+	// T is an interface type and x implements T
+	if Ti, ok := Tu.(*Interface); ok {
+		if m, wrongType := MissingMethod(x.typ, Ti, true); m != nil /* Implements(x.typ, Ti) */ {
+			if reason != nil {
+				if wrongType {
+					*reason = "wrong type for method " + m.Name()
+				} else {
+					*reason = "missing method " + m.Name()
+				}
+			}
+			return false
+		}
+		return true
+	}
+
+	// x is a bidirectional channel value, T is a channel
+	// type, x's type V and T have identical element types,
+	// and at least one of V or T is not a named type
+	if Vc, ok := Vu.(*Chan); ok && Vc.dir == SendRecv {
+		if Tc, ok := Tu.(*Chan); ok && Identical(Vc.elem, Tc.elem) {
+			return !isNamed(V) || !isNamed(T)
+		}
+	}
+
+	return false
+}

third_party/forked/golang/go/types/ordering.go

+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements resolveOrder.
+
+package types
+
+import (
+	"go/ast"
+	"sort"
+)
+
+// resolveOrder computes the order in which package-level objects
+// must be type-checked.
+//
+// Interface types appear first in the list, sorted topologically
+// by dependencies on embedded interfaces that are also declared
+// in this package, followed by all other objects sorted in source
+// order.
+//
+// TODO(gri) Consider sorting all types by dependencies here, and
+// in the process check _and_ report type cycles. This may simplify
+// the full type-checking phase.
+//
+func (check *Checker) resolveOrder() []Object {
+	var ifaces, others []Object
+
+	// collect interface types with their dependencies, and all other objects
+	for obj := range check.objMap {
+		if ityp := check.interfaceFor(obj); ityp != nil {
+			ifaces = append(ifaces, obj)
+			// determine dependencies on embedded interfaces
+			for _, f := range ityp.Methods.List {
+				if len(f.Names) == 0 {
+					// Embedded interface: The type must be a (possibly
+					// qualified) identifier denoting another interface.
+					// Imported interfaces are already fully resolved,
+					// so we can ignore qualified identifiers.
+					if ident, _ := f.Type.(*ast.Ident); ident != nil {
+						embedded := check.pkg.scope.Lookup(ident.Name)
+						if check.interfaceFor(embedded) != nil {
+							check.objMap[obj].addDep(embedded)
+						}
+					}
+				}
+			}
+		} else {
+			others = append(others, obj)
+		}
+	}
+
+	// final object order
+	var order []Object
+
+	// sort interface types topologically by dependencies,
+	// and in source order if there are no dependencies
+	sort.Sort(inSourceOrder(ifaces))
+	visited := make(objSet)
+	for _, obj := range ifaces {
+		check.appendInPostOrder(&order, obj, visited)
+	}
+
+	// sort everything else in source order
+	sort.Sort(inSourceOrder(others))
+
+	return append(order, others...)
+}
+
+// interfaceFor returns the AST interface denoted by obj, or nil.
+func (check *Checker) interfaceFor(obj Object) *ast.InterfaceType {
+	tname, _ := obj.(*TypeName)
+	if tname == nil {
+		return nil // not a type
+	}
+	d := check.objMap[obj]
+	if d == nil {
+		check.dump("%s: %s should have been declared", obj.Pos(), obj.Name())
+		unreachable()
+	}
+	if d.typ == nil {
+		return nil // invalid AST - ignore (will be handled later)
+	}
+	ityp, _ := d.typ.(*ast.InterfaceType)
+	return ityp
+}
+
+func (check *Checker) appendInPostOrder(order *[]Object, obj Object, visited objSet) {
+	if visited[obj] {
+		// We've already seen this object; either because it's
+		// already added to order, or because we have a cycle.
+		// In both cases we stop. Cycle errors are reported
+		// when type-checking types.
+		return
+	}
+	visited[obj] = true
+
+	d := check.objMap[obj]
+	for _, obj := range orderedSetObjects(d.deps) {
+		check.appendInPostOrder(order, obj, visited)
+	}
+
+	*order = append(*order, obj)
+}
+
+func orderedSetObjects(set objSet) []Object {
+	list := make([]Object, len(set))
+	i := 0
+	for obj := range set {
+		// we don't care about the map element value
+		list[i] = obj
+		i++
+	}
+	sort.Sort(inSourceOrder(list))
+	return list
+}
+
+// inSourceOrder implements the sort.Sort interface.
+type inSourceOrder []Object
+
+func (a inSourceOrder) Len() int           { return len(a) }
+func (a inSourceOrder) Less(i, j int) bool { return a[i].order() < a[j].order() }
+func (a inSourceOrder) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }

third_party/forked/golang/go/types/package.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"fmt"
+	"go/token"
+)
+
+// A Package describes a Go package.
+type Package struct {
+	path     string
+	name     string
+	scope    *Scope
+	complete bool
+	imports  []*Package
+	fake     bool // scope lookup errors are silently dropped if package is fake (internal use only)
+}
+
+// NewPackage returns a new Package for the given package path and name.
+// The package is not complete and contains no explicit imports.
+func NewPackage(path, name string) *Package {
+	scope := NewScope(Universe, token.NoPos, token.NoPos, fmt.Sprintf("package %q", path))
+	return &Package{path: path, name: name, scope: scope}
+}
+
+// Path returns the package path.
+func (pkg *Package) Path() string { return pkg.path }
+
+// Name returns the package name.
+func (pkg *Package) Name() string { return pkg.name }
+
+// SetName sets the package name.
+func (pkg *Package) SetName(name string) { pkg.name = name }
+
+// Scope returns the (complete or incomplete) package scope
+// holding the objects declared at package level (TypeNames,
+// Consts, Vars, and Funcs).
+func (pkg *Package) Scope() *Scope { return pkg.scope }
+
+// A package is complete if its scope contains (at least) all
+// exported objects; otherwise it is incomplete.
+func (pkg *Package) Complete() bool { return pkg.complete }
+
+// MarkComplete marks a package as complete.
+func (pkg *Package) MarkComplete() { pkg.complete = true }
+
+// Imports returns the list of packages directly imported by
+// pkg; the list is in source order.
+//
+// If pkg was loaded from export data, Imports includes packages that
+// provide package-level objects referenced by pkg. This may be more or
+// less than the set of packages directly imported by pkg's source code.
+func (pkg *Package) Imports() []*Package { return pkg.imports }
+
+// SetImports sets the list of explicitly imported packages to list.
+// It is the caller's responsibility to make sure list elements are unique.
+func (pkg *Package) SetImports(list []*Package) { pkg.imports = list }
+
+func (pkg *Package) String() string {
+	return fmt.Sprintf("package %s (%q)", pkg.name, pkg.path)
+}

third_party/forked/golang/go/types/predicates.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements commonly used type predicates.
+
+package types
+
+import "sort"
+
+func isNamed(typ Type) bool {
+	if _, ok := typ.(*Basic); ok {
+		return ok
+	}
+	_, ok := typ.(*Named)
+	return ok
+}
+
+func isBoolean(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsBoolean != 0
+}
+
+func isInteger(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsInteger != 0
+}
+
+func isUnsigned(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsUnsigned != 0
+}
+
+func isFloat(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsFloat != 0
+}
+
+func isComplex(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsComplex != 0
+}
+
+func isNumeric(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsNumeric != 0
+}
+
+func isString(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsString != 0
+}
+
+func isTyped(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return !ok || t.info&IsUntyped == 0
+}
+
+func isUntyped(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsUntyped != 0
+}
+
+func isOrdered(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsOrdered != 0
+}
+
+func isConstType(typ Type) bool {
+	t, ok := typ.Underlying().(*Basic)
+	return ok && t.info&IsConstType != 0
+}
+
+// IsInterface reports whether typ is an interface type.
+func IsInterface(typ Type) bool {
+	_, ok := typ.Underlying().(*Interface)
+	return ok
+}
+
+// Comparable reports whether values of type T are comparable.
+func Comparable(T Type) bool {
+	switch t := T.Underlying().(type) {
+	case *Basic:
+		// assume invalid types to be comparable
+		// to avoid follow-up errors
+		return t.kind != UntypedNil
+	case *Pointer, *Interface, *Chan:
+		return true
+	case *Struct:
+		for _, f := range t.fields {
+			if !Comparable(f.typ) {
+				return false
+			}
+		}
+		return true
+	case *Array:
+		return Comparable(t.elem)
+	}
+	return false
+}
+
+// hasNil reports whether a type includes the nil value.
+func hasNil(typ Type) bool {
+	switch t := typ.Underlying().(type) {
+	case *Basic:
+		return t.kind == UnsafePointer
+	case *Slice, *Pointer, *Signature, *Interface, *Map, *Chan:
+		return true
+	}
+	return false
+}
+
+// Identical reports whether x and y are identical types.
+// Receivers of Signature types are ignored.
+func Identical(x, y Type) bool {
+	return identical(x, y, true, nil)
+}
+
+// IdenticalIgnoreTags reports whether x and y are identical types if tags are ignored.
+// Receivers of Signature types are ignored.
+func IdenticalIgnoreTags(x, y Type) bool {
+	return identical(x, y, false, nil)
+}
+
+// An ifacePair is a node in a stack of interface type pairs compared for identity.
+type ifacePair struct {
+	x, y *Interface
+	prev *ifacePair
+}
+
+func (p *ifacePair) identical(q *ifacePair) bool {
+	return p.x == q.x && p.y == q.y || p.x == q.y && p.y == q.x
+}
+
+func identical(x, y Type, cmpTags bool, p *ifacePair) bool {
+	if x == y {
+		return true
+	}
+
+	switch x := x.(type) {
+	case *Basic:
+		// Basic types are singletons except for the rune and byte
+		// aliases, thus we cannot solely rely on the x == y check
+		// above. See also comment in TypeName.IsAlias.
+		if y, ok := y.(*Basic); ok {
+			return x.kind == y.kind
+		}
+
+	case *Array:
+		// Two array types are identical if they have identical element types
+		// and the same array length.
+		if y, ok := y.(*Array); ok {
+			// If one or both array lengths are unknown (< 0) due to some error,
+			// assume they are the same to avoid spurious follow-on errors.
+			return (x.len < 0 || y.len < 0 || x.len == y.len) && identical(x.elem, y.elem, cmpTags, p)
+		}
+
+	case *Slice:
+		// Two slice types are identical if they have identical element types.
+		if y, ok := y.(*Slice); ok {
+			return identical(x.elem, y.elem, cmpTags, p)
+		}
+
+	case *Struct:
+		// Two struct types are identical if they have the same sequence of fields,
+		// and if corresponding fields have the same names, and identical types,
+		// and identical tags. Two anonymous fields are considered to have the same
+		// name. Lower-case field names from different packages are always different.
+		if y, ok := y.(*Struct); ok {
+			if x.NumFields() == y.NumFields() {
+				for i, f := range x.fields {
+					g := y.fields[i]
+					if f.anonymous != g.anonymous ||
+						cmpTags && x.Tag(i) != y.Tag(i) ||
+						!f.sameId(g.pkg, g.name) ||
+						!identical(f.typ, g.typ, cmpTags, p) {
+						return false
+					}
+				}
+				return true
+			}
+		}
+
+	case *Pointer:
+		// Two pointer types are identical if they have identical base types.
+		if y, ok := y.(*Pointer); ok {
+			return identical(x.base, y.base, cmpTags, p)
+		}
+
+	case *Tuple:
+		// Two tuples types are identical if they have the same number of elements
+		// and corresponding elements have identical types.
+		if y, ok := y.(*Tuple); ok {
+			if x.Len() == y.Len() {
+				if x != nil {
+					for i, v := range x.vars {
+						w := y.vars[i]
+						if !identical(v.typ, w.typ, cmpTags, p) {
+							return false
+						}
+					}
+				}
+				return true
+			}
+		}
+
+	case *Signature:
+		// Two function types are identical if they have the same number of parameters
+		// and result values, corresponding parameter and result types are identical,
+		// and either both functions are variadic or neither is. Parameter and result
+		// names are not required to match.
+		if y, ok := y.(*Signature); ok {
+			return x.variadic == y.variadic &&
+				identical(x.params, y.params, cmpTags, p) &&
+				identical(x.results, y.results, cmpTags, p)
+		}
+
+	case *Interface:
+		// Two interface types are identical if they have the same set of methods with
+		// the same names and identical function types. Lower-case method names from
+		// different packages are always different. The order of the methods is irrelevant.
+		if y, ok := y.(*Interface); ok {
+			a := x.allMethods
+			b := y.allMethods
+			if len(a) == len(b) {
+				// Interface types are the only types where cycles can occur
+				// that are not "terminated" via named types; and such cycles
+				// can only be created via method parameter types that are
+				// anonymous interfaces (directly or indirectly) embedding
+				// the current interface. Example:
+				//
+				//    type T interface {
+				//        m() interface{T}
+				//    }
+				//
+				// If two such (differently named) interfaces are compared,
+				// endless recursion occurs if the cycle is not detected.
+				//
+				// If x and y were compared before, they must be equal
+				// (if they were not, the recursion would have stopped);
+				// search the ifacePair stack for the same pair.
+				//
+				// This is a quadratic algorithm, but in practice these stacks
+				// are extremely short (bounded by the nesting depth of interface
+				// type declarations that recur via parameter types, an extremely
+				// rare occurrence). An alternative implementation might use a
+				// "visited" map, but that is probably less efficient overall.
+				q := &ifacePair{x, y, p}
+				for p != nil {
+					if p.identical(q) {
+						return true // same pair was compared before
+					}
+					p = p.prev
+				}
+				if debug {
+					assert(sort.IsSorted(byUniqueMethodName(a)))
+					assert(sort.IsSorted(byUniqueMethodName(b)))
+				}
+				for i, f := range a {
+					g := b[i]
+					if f.Id() != g.Id() || !identical(f.typ, g.typ, cmpTags, q) {
+						return false
+					}
+				}
+				return true
+			}
+		}
+
+	case *Map:
+		// Two map types are identical if they have identical key and value types.
+		if y, ok := y.(*Map); ok {
+			return identical(x.key, y.key, cmpTags, p) && identical(x.elem, y.elem, cmpTags, p)
+		}
+
+	case *Chan:
+		// Two channel types are identical if they have identical value types
+		// and the same direction.
+		if y, ok := y.(*Chan); ok {
+			return x.dir == y.dir && identical(x.elem, y.elem, cmpTags, p)
+		}
+
+	case *Named:
+		// Two named types are identical if their type names originate
+		// in the same type declaration.
+		if y, ok := y.(*Named); ok {
+			return x.obj == y.obj
+		}
+
+	case nil:
+
+	default:
+		unreachable()
+	}
+
+	return false
+}
+
+// Default returns the default "typed" type for an "untyped" type;
+// it returns the incoming type for all other types. The default type
+// for untyped nil is untyped nil.
+//
+func Default(typ Type) Type {
+	if t, ok := typ.(*Basic); ok {
+		switch t.kind {
+		case UntypedBool:
+			return Typ[Bool]
+		case UntypedInt:
+			return Typ[Int]
+		case UntypedRune:
+			return universeRune // use 'rune' name
+		case UntypedFloat:
+			return Typ[Float64]
+		case UntypedComplex:
+			return Typ[Complex128]
+		case UntypedString:
+			return Typ[String]
+		}
+	}
+	return typ
+}

third_party/forked/golang/go/types/resolver.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"strconv"
+	"strings"
+	"unicode"
+)
+
+// A declInfo describes a package-level const, type, var, or func declaration.
+type declInfo struct {
+	file  *Scope        // scope of file containing this declaration
+	lhs   []*Var        // lhs of n:1 variable declarations, or nil
+	typ   ast.Expr      // type, or nil
+	init  ast.Expr      // init/orig expression, or nil
+	fdecl *ast.FuncDecl // func declaration, or nil
+	alias bool          // type alias declaration
+
+	// The deps field tracks initialization expression dependencies.
+	// As a special (overloaded) case, it also tracks dependencies of
+	// interface types on embedded interfaces (see ordering.go).
+	deps objSet // lazily initialized
+}
+
+// An objSet is simply a set of objects.
+type objSet map[Object]bool
+
+// hasInitializer reports whether the declared object has an initialization
+// expression or function body.
+func (d *declInfo) hasInitializer() bool {
+	return d.init != nil || d.fdecl != nil && d.fdecl.Body != nil
+}
+
+// addDep adds obj to the set of objects d's init expression depends on.
+func (d *declInfo) addDep(obj Object) {
+	m := d.deps
+	if m == nil {
+		m = make(objSet)
+		d.deps = m
+	}
+	m[obj] = true
+}
+
+// arityMatch checks that the lhs and rhs of a const or var decl
+// have the appropriate number of names and init exprs. For const
+// decls, init is the value spec providing the init exprs; for
+// var decls, init is nil (the init exprs are in s in this case).
+func (check *Checker) arityMatch(s, init *ast.ValueSpec) {
+	l := len(s.Names)
+	r := len(s.Values)
+	if init != nil {
+		r = len(init.Values)
+	}
+
+	switch {
+	case init == nil && r == 0:
+		// var decl w/o init expr
+		if s.Type == nil {
+			check.errorf(s.Pos(), "missing type or init expr")
+		}
+	case l < r:
+		if l < len(s.Values) {
+			// init exprs from s
+			n := s.Values[l]
+			check.errorf(n.Pos(), "extra init expr %s", n)
+			// TODO(gri) avoid declared but not used error here
+		} else {
+			// init exprs "inherited"
+			check.errorf(s.Pos(), "extra init expr at %s", check.fset.Position(init.Pos()))
+			// TODO(gri) avoid declared but not used error here
+		}
+	case l > r && (init != nil || r != 1):
+		n := s.Names[r]
+		check.errorf(n.Pos(), "missing init expr for %s", n)
+	}
+}
+
+func validatedImportPath(path string) (string, error) {
+	s, err := strconv.Unquote(path)
+	if err != nil {
+		return "", err
+	}
+	if s == "" {
+		return "", fmt.Errorf("empty string")
+	}
+	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
+	for _, r := range s {
+		if !unicode.IsGraphic(r) || unicode.IsSpace(r) || strings.ContainsRune(illegalChars, r) {
+			return s, fmt.Errorf("invalid character %#U", r)
+		}
+	}
+	return s, nil
+}
+
+// declarePkgObj declares obj in the package scope, records its ident -> obj mapping,
+// and updates check.objMap. The object must not be a function or method.
+func (check *Checker) declarePkgObj(ident *ast.Ident, obj Object, d *declInfo) {
+	assert(ident.Name == obj.Name())
+
+	// spec: "A package-scope or file-scope identifier with name init
+	// may only be declared to be a function with this (func()) signature."
+	if ident.Name == "init" {
+		check.errorf(ident.Pos(), "cannot declare init - must be func")
+		return
+	}
+
+	// spec: "The main package must have package name main and declare
+	// a function main that takes no arguments and returns no value."
+	if ident.Name == "main" && check.pkg.name == "main" {
+		check.errorf(ident.Pos(), "cannot declare main - must be func")
+		return
+	}
+
+	check.declare(check.pkg.scope, ident, obj, token.NoPos)
+	check.objMap[obj] = d
+	obj.setOrder(uint32(len(check.objMap)))
+}
+
+// filename returns a filename suitable for debugging output.
+func (check *Checker) filename(fileNo int) string {
+	file := check.files[fileNo]
+	if pos := file.Pos(); pos.IsValid() {
+		return check.fset.File(pos).Name()
+	}
+	return fmt.Sprintf("file[%d]", fileNo)
+}
+
+func (check *Checker) importPackage(pos token.Pos, path, dir string) *Package {
+	// If we already have a package for the given (path, dir)
+	// pair, use it instead of doing a full import.
+	// Checker.impMap only caches packages that are marked Complete
+	// or fake (dummy packages for failed imports). Incomplete but
+	// non-fake packages do require an import to complete them.
+	key := importKey{path, dir}
+	imp := check.impMap[key]
+	if imp != nil {
+		return imp
+	}
+
+	// no package yet => import it
+	if path == "C" && check.conf.FakeImportC {
+		imp = NewPackage("C", "C")
+		imp.fake = true
+	} else {
+		// ordinary import
+		var err error
+		if importer := check.conf.Importer; importer == nil {
+			err = fmt.Errorf("Config.Importer not installed")
+		} else if importerFrom, ok := importer.(ImporterFrom); ok {
+			imp, err = importerFrom.ImportFrom(path, dir, 0)
+			if imp == nil && err == nil {
+				err = fmt.Errorf("Config.Importer.ImportFrom(%s, %s, 0) returned nil but no error", path, dir)
+			}
+		} else {
+			imp, err = importer.Import(path)
+			if imp == nil && err == nil {
+				err = fmt.Errorf("Config.Importer.Import(%s) returned nil but no error", path)
+			}
+		}
+		// make sure we have a valid package name
+		// (errors here can only happen through manipulation of packages after creation)
+		if err == nil && imp != nil && (imp.name == "_" || imp.name == "") {
+			err = fmt.Errorf("invalid package name: %q", imp.name)
+			imp = nil // create fake package below
+		}
+		if err != nil {
+			check.errorf(pos, "could not import %s (%s)", path, err)
+			if imp == nil {
+				// create a new fake package
+				// come up with a sensible package name (heuristic)
+				name := path
+				if i := len(name); i > 0 && name[i-1] == '/' {
+					name = name[:i-1]
+				}
+				if i := strings.LastIndex(name, "/"); i >= 0 {
+					name = name[i+1:]
+				}
+				imp = NewPackage(path, name)
+			}
+			// continue to use the package as best as we can
+			imp.fake = true // avoid follow-up lookup failures
+		}
+	}
+
+	// package should be complete or marked fake, but be cautious
+	if imp.complete || imp.fake {
+		check.impMap[key] = imp
+		return imp
+	}
+
+	// something went wrong (importer may have returned incomplete package without error)
+	return nil
+}
+
+// collectObjects collects all file and package objects and inserts them
+// into their respective scopes. It also performs imports and associates
+// methods with receiver base type names.
+func (check *Checker) collectObjects() {
+	pkg := check.pkg
+
+	// pkgImports is the set of packages already imported by any package file seen
+	// so far. Used to avoid duplicate entries in pkg.imports. Allocate and populate
+	// it (pkg.imports may not be empty if we are checking test files incrementally).
+	// Note that pkgImports is keyed by package (and thus package path), not by an
+	// importKey value. Two different importKey values may map to the same package
+	// which is why we cannot use the check.impMap here.
+	var pkgImports = make(map[*Package]bool)
+	for _, imp := range pkg.imports {
+		pkgImports[imp] = true
+	}
+
+	for fileNo, file := range check.files {
+		// The package identifier denotes the current package,
+		// but there is no corresponding package object.
+		check.recordDef(file.Name, nil)
+
+		// Use the actual source file extent rather than *ast.File extent since the
+		// latter doesn't include comments which appear at the start or end of the file.
+		// Be conservative and use the *ast.File extent if we don't have a *token.File.
+		pos, end := file.Pos(), file.End()
+		if f := check.fset.File(file.Pos()); f != nil {
+			pos, end = token.Pos(f.Base()), token.Pos(f.Base()+f.Size())
+		}
+		fileScope := NewScope(check.pkg.scope, pos, end, check.filename(fileNo))
+		check.recordScope(file, fileScope)
+
+		// determine file directory, necessary to resolve imports
+		// FileName may be "" (typically for tests) in which case
+		// we get "." as the directory which is what we would want.
+		fileDir := dir(check.fset.Position(file.Name.Pos()).Filename)
+
+		for _, decl := range file.Decls {
+			switch d := decl.(type) {
+			case *ast.BadDecl:
+				// ignore
+
+			case *ast.GenDecl:
+				var last *ast.ValueSpec // last ValueSpec with type or init exprs seen
+				for iota, spec := range d.Specs {
+					switch s := spec.(type) {
+					case *ast.ImportSpec:
+						// import package
+						path, err := validatedImportPath(s.Path.Value)
+						if err != nil {
+							check.errorf(s.Path.Pos(), "invalid import path (%s)", err)
+							continue
+						}
+
+						imp := check.importPackage(s.Path.Pos(), path, fileDir)
+						if imp == nil {
+							continue
+						}
+
+						// add package to list of explicit imports
+						// (this functionality is provided as a convenience
+						// for clients; it is not needed for type-checking)
+						if !pkgImports[imp] {
+							pkgImports[imp] = true
+							pkg.imports = append(pkg.imports, imp)
+						}
+
+						// local name overrides imported package name
+						name := imp.name
+						if s.Name != nil {
+							name = s.Name.Name
+							if path == "C" {
+								// match cmd/compile (not prescribed by spec)
+								check.errorf(s.Name.Pos(), `cannot rename import "C"`)
+								continue
+							}
+							if name == "init" {
+								check.errorf(s.Name.Pos(), "cannot declare init - must be func")
+								continue
+							}
+						}
+
+						obj := NewPkgName(s.Pos(), pkg, name, imp)
+						if s.Name != nil {
+							// in a dot-import, the dot represents the package
+							check.recordDef(s.Name, obj)
+						} else {
+							check.recordImplicit(s, obj)
+						}
+
+						if path == "C" {
+							// match cmd/compile (not prescribed by spec)
+							obj.used = true
+						}
+
+						// add import to file scope
+						if name == "." {
+							// merge imported scope with file scope
+							for _, obj := range imp.scope.elems {
+								// A package scope may contain non-exported objects,
+								// do not import them!
+								if obj.Exported() {
+									// TODO(gri) When we import a package, we create
+									// a new local package object. We should do the
+									// same for each dot-imported object. That way
+									// they can have correct position information.
+									// (We must not modify their existing position
+									// information because the same package - found
+									// via Config.Packages - may be dot-imported in
+									// another package!)
+									check.declare(fileScope, nil, obj, token.NoPos)
+								}
+							}
+							// add position to set of dot-import positions for this file
+							// (this is only needed for "imported but not used" errors)
+							check.addUnusedDotImport(fileScope, imp, s.Pos())
+						} else {
+							// declare imported package object in file scope
+							check.declare(fileScope, nil, obj, token.NoPos)
+						}
+
+					case *ast.ValueSpec:
+						switch d.Tok {
+						case token.CONST:
+							// determine which initialization expressions to use
+							switch {
+							case s.Type != nil || len(s.Values) > 0:
+								last = s
+							case last == nil:
+								last = new(ast.ValueSpec) // make sure last exists
+							}
+
+							// declare all constants
+							for i, name := range s.Names {
+								obj := NewConst(name.Pos(), pkg, name.Name, nil, constant.MakeInt64(int64(iota)))
+
+								var init ast.Expr
+								if i < len(last.Values) {
+									init = last.Values[i]
+								}
+
+								d := &declInfo{file: fileScope, typ: last.Type, init: init}
+								check.declarePkgObj(name, obj, d)
+							}
+
+							check.arityMatch(s, last)
+
+						case token.VAR:
+							lhs := make([]*Var, len(s.Names))
+							// If there's exactly one rhs initializer, use
+							// the same declInfo d1 for all lhs variables
+							// so that each lhs variable depends on the same
+							// rhs initializer (n:1 var declaration).
+							var d1 *declInfo
+							if len(s.Values) == 1 {
+								// The lhs elements are only set up after the for loop below,
+								// but that's ok because declareVar only collects the declInfo
+								// for a later phase.
+								d1 = &declInfo{file: fileScope, lhs: lhs, typ: s.Type, init: s.Values[0]}
+							}
+
+							// declare all variables
+							for i, name := range s.Names {
+								obj := NewVar(name.Pos(), pkg, name.Name, nil)
+								lhs[i] = obj
+
+								d := d1
+								if d == nil {
+									// individual assignments
+									var init ast.Expr
+									if i < len(s.Values) {
+										init = s.Values[i]
+									}
+									d = &declInfo{file: fileScope, typ: s.Type, init: init}
+								}
+
+								check.declarePkgObj(name, obj, d)
+							}
+
+							check.arityMatch(s, nil)
+
+						default:
+							check.invalidAST(s.Pos(), "invalid token %s", d.Tok)
+						}
+
+					case *ast.TypeSpec:
+						obj := NewTypeName(s.Name.Pos(), pkg, s.Name.Name, nil)
+						check.declarePkgObj(s.Name, obj, &declInfo{file: fileScope, typ: s.Type, alias: s.Assign.IsValid()})
+
+					default:
+						check.invalidAST(s.Pos(), "unknown ast.Spec node %T", s)
+					}
+				}
+
+			case *ast.FuncDecl:
+				name := d.Name.Name
+				obj := NewFunc(d.Name.Pos(), pkg, name, nil)
+				if d.Recv == nil {
+					// regular function
+					if name == "init" {
+						// don't declare init functions in the package scope - they are invisible
+						obj.parent = pkg.scope
+						check.recordDef(d.Name, obj)
+						// init functions must have a body
+						if d.Body == nil {
+							check.softErrorf(obj.pos, "missing function body")
+						}
+					} else {
+						check.declare(pkg.scope, d.Name, obj, token.NoPos)
+					}
+				} else {
+					// method
+					check.recordDef(d.Name, obj)
+					// Associate method with receiver base type name, if possible.
+					// Ignore methods that have an invalid receiver, or a blank _
+					// receiver name. They will be type-checked later, with regular
+					// functions.
+					if list := d.Recv.List; len(list) > 0 {
+						typ := unparen(list[0].Type)
+						if ptr, _ := typ.(*ast.StarExpr); ptr != nil {
+							typ = unparen(ptr.X)
+						}
+						if base, _ := typ.(*ast.Ident); base != nil && base.Name != "_" {
+							check.assocMethod(base.Name, obj)
+						}
+					}
+				}
+				info := &declInfo{file: fileScope, fdecl: d}
+				check.objMap[obj] = info
+				obj.setOrder(uint32(len(check.objMap)))
+
+			default:
+				check.invalidAST(d.Pos(), "unknown ast.Decl node %T", d)
+			}
+		}
+	}
+
+	// verify that objects in package and file scopes have different names
+	for _, scope := range check.pkg.scope.children /* file scopes */ {
+		for _, obj := range scope.elems {
+			if alt := pkg.scope.Lookup(obj.Name()); alt != nil {
+				if pkg, ok := obj.(*PkgName); ok {
+					check.errorf(alt.Pos(), "%s already declared through import of %s", alt.Name(), pkg.Imported())
+					check.reportAltDecl(pkg)
+				} else {
+					check.errorf(alt.Pos(), "%s already declared through dot-import of %s", alt.Name(), obj.Pkg())
+					// TODO(gri) dot-imported objects don't have a position; reportAltDecl won't print anything
+					check.reportAltDecl(obj)
+				}
+			}
+		}
+	}
+}
+
+// packageObjects typechecks all package objects in objList, but not function bodies.
+func (check *Checker) packageObjects(objList []Object) {
+	// add new methods to already type-checked types (from a prior Checker.Files call)
+	for _, obj := range objList {
+		if obj, _ := obj.(*TypeName); obj != nil && obj.typ != nil {
+			check.addMethodDecls(obj)
+		}
+	}
+
+	// pre-allocate space for type declaration paths so that the underlying array is reused
+	typePath := make([]*TypeName, 0, 8)
+
+	for _, obj := range objList {
+		check.objDecl(obj, nil, typePath)
+	}
+
+	// At this point we may have a non-empty check.methods map; this means that not all
+	// entries were deleted at the end of typeDecl because the respective receiver base
+	// types were not found. In that case, an error was reported when declaring those
+	// methods. We can now safely discard this map.
+	check.methods = nil
+}
+
+// functionBodies typechecks all function bodies.
+func (check *Checker) functionBodies() {
+	for _, f := range check.funcs {
+		check.funcBody(f.decl, f.name, f.sig, f.body)
+	}
+}
+
+// unusedImports checks for unused imports.
+func (check *Checker) unusedImports() {
+	// if function bodies are not checked, packages' uses are likely missing - don't check
+	if check.conf.IgnoreFuncBodies {
+		return
+	}
+
+	// spec: "It is illegal (...) to directly import a package without referring to
+	// any of its exported identifiers. To import a package solely for its side-effects
+	// (initialization), use the blank identifier as explicit package name."
+
+	// check use of regular imported packages
+	for _, scope := range check.pkg.scope.children /* file scopes */ {
+		for _, obj := range scope.elems {
+			if obj, ok := obj.(*PkgName); ok {
+				// Unused "blank imports" are automatically ignored
+				// since _ identifiers are not entered into scopes.
+				if !obj.used {
+					path := obj.imported.path
+					base := pkgName(path)
+					if obj.name == base {
+						check.softErrorf(obj.pos, "%q imported but not used", path)
+					} else {
+						check.softErrorf(obj.pos, "%q imported but not used as %s", path, obj.name)
+					}
+				}
+			}
+		}
+	}
+
+	// check use of dot-imported packages
+	for _, unusedDotImports := range check.unusedDotImports {
+		for pkg, pos := range unusedDotImports {
+			check.softErrorf(pos, "%q imported but not used", pkg.path)
+		}
+	}
+}
+
+// pkgName returns the package name (last element) of an import path.
+func pkgName(path string) string {
+	if i := strings.LastIndex(path, "/"); i >= 0 {
+		path = path[i+1:]
+	}
+	return path
+}
+
+// dir makes a good-faith attempt to return the directory
+// portion of path. If path is empty, the result is ".".
+// (Per the go/build package dependency tests, we cannot import
+// path/filepath and simply use filepath.Dir.)
+func dir(path string) string {
+	if i := strings.LastIndexAny(path, `/\`); i > 0 {
+		return path[:i]
+	}
+	// i <= 0
+	return "."
+}

third_party/forked/golang/go/types/return.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements isTerminating.
+
+package types
+
+import (
+	"go/ast"
+	"go/token"
+)
+
+// isTerminating reports if s is a terminating statement.
+// If s is labeled, label is the label name; otherwise s
+// is "".
+func (check *Checker) isTerminating(s ast.Stmt, label string) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.SendStmt,
+		*ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt, *ast.DeferStmt,
+		*ast.RangeStmt:
+		// no chance
+
+	case *ast.LabeledStmt:
+		return check.isTerminating(s.Stmt, s.Label.Name)
+
+	case *ast.ExprStmt:
+		// the predeclared (possibly parenthesized) panic() function is terminating
+		if call, _ := unparen(s.X).(*ast.CallExpr); call != nil {
+			if id, _ := call.Fun.(*ast.Ident); id != nil {
+				if _, obj := check.scope.LookupParent(id.Name, token.NoPos); obj != nil {
+					if b, _ := obj.(*Builtin); b != nil && b.id == _Panic {
+						return true
+					}
+				}
+			}
+		}
+
+	case *ast.ReturnStmt:
+		return true
+
+	case *ast.BranchStmt:
+		if s.Tok == token.GOTO || s.Tok == token.FALLTHROUGH {
+			return true
+		}
+
+	case *ast.BlockStmt:
+		return check.isTerminatingList(s.List, "")
+
+	case *ast.IfStmt:
+		if s.Else != nil &&
+			check.isTerminating(s.Body, "") &&
+			check.isTerminating(s.Else, "") {
+			return true
+		}
+
+	case *ast.SwitchStmt:
+		return check.isTerminatingSwitch(s.Body, label)
+
+	case *ast.TypeSwitchStmt:
+		return check.isTerminatingSwitch(s.Body, label)
+
+	case *ast.SelectStmt:
+		for _, s := range s.Body.List {
+			cc := s.(*ast.CommClause)
+			if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+				return false
+			}
+
+		}
+		return true
+
+	case *ast.ForStmt:
+		if s.Cond == nil && !hasBreak(s.Body, label, true) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (check *Checker) isTerminatingList(list []ast.Stmt, label string) bool {
+	// trailing empty statements are permitted - skip them
+	for i := len(list) - 1; i >= 0; i-- {
+		if _, ok := list[i].(*ast.EmptyStmt); !ok {
+			return check.isTerminating(list[i], label)
+		}
+	}
+	return false // all statements are empty
+}
+
+func (check *Checker) isTerminatingSwitch(body *ast.BlockStmt, label string) bool {
+	hasDefault := false
+	for _, s := range body.List {
+		cc := s.(*ast.CaseClause)
+		if cc.List == nil {
+			hasDefault = true
+		}
+		if !check.isTerminatingList(cc.Body, "") || hasBreakList(cc.Body, label, true) {
+			return false
+		}
+	}
+	return hasDefault
+}
+
+// TODO(gri) For nested breakable statements, the current implementation of hasBreak
+//	     will traverse the same subtree repeatedly, once for each label. Replace
+//           with a single-pass label/break matching phase.
+
+// hasBreak reports if s is or contains a break statement
+// referring to the label-ed statement or implicit-ly the
+// closest outer breakable statement.
+func hasBreak(s ast.Stmt, label string, implicit bool) bool {
+	switch s := s.(type) {
+	default:
+		unreachable()
+
+	case *ast.BadStmt, *ast.DeclStmt, *ast.EmptyStmt, *ast.ExprStmt,
+		*ast.SendStmt, *ast.IncDecStmt, *ast.AssignStmt, *ast.GoStmt,
+		*ast.DeferStmt, *ast.ReturnStmt:
+		// no chance
+
+	case *ast.LabeledStmt:
+		return hasBreak(s.Stmt, label, implicit)
+
+	case *ast.BranchStmt:
+		if s.Tok == token.BREAK {
+			if s.Label == nil {
+				return implicit
+			}
+			if s.Label.Name == label {
+				return true
+			}
+		}
+
+	case *ast.BlockStmt:
+		return hasBreakList(s.List, label, implicit)
+
+	case *ast.IfStmt:
+		if hasBreak(s.Body, label, implicit) ||
+			s.Else != nil && hasBreak(s.Else, label, implicit) {
+			return true
+		}
+
+	case *ast.CaseClause:
+		return hasBreakList(s.Body, label, implicit)
+
+	case *ast.SwitchStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.TypeSwitchStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.CommClause:
+		return hasBreakList(s.Body, label, implicit)
+
+	case *ast.SelectStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.ForStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+
+	case *ast.RangeStmt:
+		if label != "" && hasBreak(s.Body, label, false) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func hasBreakList(list []ast.Stmt, label string, implicit bool) bool {
+	for _, s := range list {
+		if hasBreak(s, label, implicit) {
+			return true
+		}
+	}
+	return false
+}

third_party/forked/golang/go/types/scope.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements Scopes.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+	"go/token"
+	"io"
+	"sort"
+	"strings"
+)
+
+// TODO(gri) Provide scopes with a name or other mechanism so that
+//           objects can use that information for better printing.
+
+// A Scope maintains a set of objects and links to its containing
+// (parent) and contained (children) scopes. Objects may be inserted
+// and looked up by name. The zero value for Scope is a ready-to-use
+// empty scope.
+type Scope struct {
+	parent   *Scope
+	children []*Scope
+	elems    map[string]Object // lazily allocated
+	pos, end token.Pos         // scope extent; may be invalid
+	comment  string            // for debugging only
+	isFunc   bool              // set if this is a function scope (internal use only)
+}
+
+// NewScope returns a new, empty scope contained in the given parent
+// scope, if any. The comment is for debugging only.
+func NewScope(parent *Scope, pos, end token.Pos, comment string) *Scope {
+	s := &Scope{parent, nil, nil, pos, end, comment, false}
+	// don't add children to Universe scope!
+	if parent != nil && parent != Universe {
+		parent.children = append(parent.children, s)
+	}
+	return s
+}
+
+// Parent returns the scope's containing (parent) scope.
+func (s *Scope) Parent() *Scope { return s.parent }
+
+// Len() returns the number of scope elements.
+func (s *Scope) Len() int { return len(s.elems) }
+
+// Names returns the scope's element names in sorted order.
+func (s *Scope) Names() []string {
+	names := make([]string, len(s.elems))
+	i := 0
+	for name := range s.elems {
+		names[i] = name
+		i++
+	}
+	sort.Strings(names)
+	return names
+}
+
+// NumChildren() returns the number of scopes nested in s.
+func (s *Scope) NumChildren() int { return len(s.children) }
+
+// Child returns the i'th child scope for 0 <= i < NumChildren().
+func (s *Scope) Child(i int) *Scope { return s.children[i] }
+
+// Lookup returns the object in scope s with the given name if such an
+// object exists; otherwise the result is nil.
+func (s *Scope) Lookup(name string) Object {
+	return s.elems[name]
+}
+
+// LookupParent follows the parent chain of scopes starting with s until
+// it finds a scope where Lookup(name) returns a non-nil object, and then
+// returns that scope and object. If a valid position pos is provided,
+// only objects that were declared at or before pos are considered.
+// If no such scope and object exists, the result is (nil, nil).
+//
+// Note that obj.Parent() may be different from the returned scope if the
+// object was inserted into the scope and already had a parent at that
+// time (see Insert, below). This can only happen for dot-imported objects
+// whose scope is the scope of the package that exported them.
+func (s *Scope) LookupParent(name string, pos token.Pos) (*Scope, Object) {
+	for ; s != nil; s = s.parent {
+		if obj := s.elems[name]; obj != nil && (!pos.IsValid() || obj.scopePos() <= pos) {
+			return s, obj
+		}
+	}
+	return nil, nil
+}
+
+// Insert attempts to insert an object obj into scope s.
+// If s already contains an alternative object alt with
+// the same name, Insert leaves s unchanged and returns alt.
+// Otherwise it inserts obj, sets the object's parent scope
+// if not already set, and returns nil.
+func (s *Scope) Insert(obj Object) Object {
+	name := obj.Name()
+	if alt := s.elems[name]; alt != nil {
+		return alt
+	}
+	if s.elems == nil {
+		s.elems = make(map[string]Object)
+	}
+	s.elems[name] = obj
+	if obj.Parent() == nil {
+		obj.setParent(s)
+	}
+	return nil
+}
+
+// Pos and End describe the scope's source code extent [pos, end).
+// The results are guaranteed to be valid only if the type-checked
+// AST has complete position information. The extent is undefined
+// for Universe and package scopes.
+func (s *Scope) Pos() token.Pos { return s.pos }
+func (s *Scope) End() token.Pos { return s.end }
+
+// Contains returns true if pos is within the scope's extent.
+// The result is guaranteed to be valid only if the type-checked
+// AST has complete position information.
+func (s *Scope) Contains(pos token.Pos) bool {
+	return s.pos <= pos && pos < s.end
+}
+
+// Innermost returns the innermost (child) scope containing
+// pos. If pos is not within any scope, the result is nil.
+// The result is also nil for the Universe scope.
+// The result is guaranteed to be valid only if the type-checked
+// AST has complete position information.
+func (s *Scope) Innermost(pos token.Pos) *Scope {
+	// Package scopes do not have extents since they may be
+	// discontiguous, so iterate over the package's files.
+	if s.parent == Universe {
+		for _, s := range s.children {
+			if inner := s.Innermost(pos); inner != nil {
+				return inner
+			}
+		}
+	}
+
+	if s.Contains(pos) {
+		for _, s := range s.children {
+			if s.Contains(pos) {
+				return s.Innermost(pos)
+			}
+		}
+		return s
+	}
+	return nil
+}
+
+// WriteTo writes a string representation of the scope to w,
+// with the scope elements sorted by name.
+// The level of indentation is controlled by n >= 0, with
+// n == 0 for no indentation.
+// If recurse is set, it also writes nested (children) scopes.
+func (s *Scope) WriteTo(w io.Writer, n int, recurse bool) {
+	const ind = ".  "
+	indn := strings.Repeat(ind, n)
+
+	fmt.Fprintf(w, "%s%s scope %p {", indn, s.comment, s)
+	if len(s.elems) == 0 {
+		fmt.Fprintf(w, "}\n")
+		return
+	}
+
+	fmt.Fprintln(w)
+	indn1 := indn + ind
+	for _, name := range s.Names() {
+		fmt.Fprintf(w, "%s%s\n", indn1, s.elems[name])
+	}
+
+	if recurse {
+		for _, s := range s.children {
+			fmt.Fprintln(w)
+			s.WriteTo(w, n+1, recurse)
+		}
+	}
+
+	fmt.Fprintf(w, "%s}", indn)
+}
+
+// String returns a string representation of the scope, for debugging.
+func (s *Scope) String() string {
+	var buf bytes.Buffer
+	s.WriteTo(&buf, 0, false)
+	return buf.String()
+}

third_party/forked/golang/go/types/selection.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements Selections.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// SelectionKind describes the kind of a selector expression x.f
+// (excluding qualified identifiers).
+type SelectionKind int
+
+const (
+	FieldVal   SelectionKind = iota // x.f is a struct field selector
+	MethodVal                       // x.f is a method selector
+	MethodExpr                      // x.f is a method expression
+)
+
+// A Selection describes a selector expression x.f.
+// For the declarations:
+//
+//	type T struct{ x int; E }
+//	type E struct{}
+//	func (e E) m() {}
+//	var p *T
+//
+// the following relations exist:
+//
+//	Selector    Kind          Recv    Obj    Type               Index     Indirect
+//
+//	p.x         FieldVal      T       x      int                {0}       true
+//	p.m         MethodVal     *T      m      func (e *T) m()    {1, 0}    true
+//	T.m         MethodExpr    T       m      func m(_ T)        {1, 0}    false
+//
+type Selection struct {
+	kind     SelectionKind
+	recv     Type   // type of x
+	obj      Object // object denoted by x.f
+	index    []int  // path from x to x.f
+	indirect bool   // set if there was any pointer indirection on the path
+}
+
+// Kind returns the selection kind.
+func (s *Selection) Kind() SelectionKind { return s.kind }
+
+// Recv returns the type of x in x.f.
+func (s *Selection) Recv() Type { return s.recv }
+
+// Obj returns the object denoted by x.f; a *Var for
+// a field selection, and a *Func in all other cases.
+func (s *Selection) Obj() Object { return s.obj }
+
+// Type returns the type of x.f, which may be different from the type of f.
+// See Selection for more information.
+func (s *Selection) Type() Type {
+	switch s.kind {
+	case MethodVal:
+		// The type of x.f is a method with its receiver type set
+		// to the type of x.
+		sig := *s.obj.(*Func).typ.(*Signature)
+		recv := *sig.recv
+		recv.typ = s.recv
+		sig.recv = &recv
+		return &sig
+
+	case MethodExpr:
+		// The type of x.f is a function (without receiver)
+		// and an additional first argument with the same type as x.
+		// TODO(gri) Similar code is already in call.go - factor!
+		// TODO(gri) Compute this eagerly to avoid allocations.
+		sig := *s.obj.(*Func).typ.(*Signature)
+		arg0 := *sig.recv
+		sig.recv = nil
+		arg0.typ = s.recv
+		var params []*Var
+		if sig.params != nil {
+			params = sig.params.vars
+		}
+		sig.params = NewTuple(append([]*Var{&arg0}, params...)...)
+		return &sig
+	}
+
+	// In all other cases, the type of x.f is the type of x.
+	return s.obj.Type()
+}
+
+// Index describes the path from x to f in x.f.
+// The last index entry is the field or method index of the type declaring f;
+// either:
+//
+//	1) the list of declared methods of a named type; or
+//	2) the list of methods of an interface type; or
+//	3) the list of fields of a struct type.
+//
+// The earlier index entries are the indices of the embedded fields implicitly
+// traversed to get from (the type of) x to f, starting at embedding depth 0.
+func (s *Selection) Index() []int { return s.index }
+
+// Indirect reports whether any pointer indirection was required to get from
+// x to f in x.f.
+func (s *Selection) Indirect() bool { return s.indirect }
+
+func (s *Selection) String() string { return SelectionString(s, nil) }
+
+// SelectionString returns the string form of s.
+// The Qualifier controls the printing of
+// package-level objects, and may be nil.
+//
+// Examples:
+//	"field (T) f int"
+//	"method (T) f(X) Y"
+//	"method expr (T) f(X) Y"
+//
+func SelectionString(s *Selection, qf Qualifier) string {
+	var k string
+	switch s.kind {
+	case FieldVal:
+		k = "field "
+	case MethodVal:
+		k = "method "
+	case MethodExpr:
+		k = "method expr "
+	default:
+		unreachable()
+	}
+	var buf bytes.Buffer
+	buf.WriteString(k)
+	buf.WriteByte('(')
+	WriteType(&buf, s.Recv(), qf)
+	fmt.Fprintf(&buf, ") %s", s.obj.Name())
+	if T := s.Type(); s.kind == FieldVal {
+		buf.WriteByte(' ')
+		WriteType(&buf, T, qf)
+	} else {
+		WriteSignature(&buf, T.(*Signature), qf)
+	}
+	return buf.String()
+}

third_party/forked/golang/go/types/sizes.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements Sizes.
+
+package types
+
+// Sizes defines the sizing functions for package unsafe.
+type Sizes interface {
+	// Alignof returns the alignment of a variable of type T.
+	// Alignof must implement the alignment guarantees required by the spec.
+	Alignof(T Type) int64
+
+	// Offsetsof returns the offsets of the given struct fields, in bytes.
+	// Offsetsof must implement the offset guarantees required by the spec.
+	Offsetsof(fields []*Var) []int64
+
+	// Sizeof returns the size of a variable of type T.
+	// Sizeof must implement the size guarantees required by the spec.
+	Sizeof(T Type) int64
+}
+
+// StdSizes is a convenience type for creating commonly used Sizes.
+// It makes the following simplifying assumptions:
+//
+//	- The size of explicitly sized basic types (int16, etc.) is the
+//	  specified size.
+//	- The size of strings and interfaces is 2*WordSize.
+//	- The size of slices is 3*WordSize.
+//	- The size of an array of n elements corresponds to the size of
+//	  a struct of n consecutive fields of the array's element type.
+//      - The size of a struct is the offset of the last field plus that
+//	  field's size. As with all element types, if the struct is used
+//	  in an array its size must first be aligned to a multiple of the
+//	  struct's alignment.
+//	- All other types have size WordSize.
+//	- Arrays and structs are aligned per spec definition; all other
+//	  types are naturally aligned with a maximum alignment MaxAlign.
+//
+// *StdSizes implements Sizes.
+//
+type StdSizes struct {
+	WordSize int64 // word size in bytes - must be >= 4 (32bits)
+	MaxAlign int64 // maximum alignment in bytes - must be >= 1
+}
+
+func (s *StdSizes) Alignof(T Type) int64 {
+	// For arrays and structs, alignment is defined in terms
+	// of alignment of the elements and fields, respectively.
+	switch t := T.Underlying().(type) {
+	case *Array:
+		// spec: "For a variable x of array type: unsafe.Alignof(x)
+		// is the same as unsafe.Alignof(x[0]), but at least 1."
+		return s.Alignof(t.elem)
+	case *Struct:
+		// spec: "For a variable x of struct type: unsafe.Alignof(x)
+		// is the largest of the values unsafe.Alignof(x.f) for each
+		// field f of x, but at least 1."
+		max := int64(1)
+		for _, f := range t.fields {
+			if a := s.Alignof(f.typ); a > max {
+				max = a
+			}
+		}
+		return max
+	case *Slice, *Interface:
+		// Multiword data structures are effectively structs
+		// in which each element has size WordSize.
+		return s.WordSize
+	case *Basic:
+		// Strings are like slices and interfaces.
+		if t.Info()&IsString != 0 {
+			return s.WordSize
+		}
+	}
+	a := s.Sizeof(T) // may be 0
+	// spec: "For a variable x of any type: unsafe.Alignof(x) is at least 1."
+	if a < 1 {
+		return 1
+	}
+	// complex{64,128} are aligned like [2]float{32,64}.
+	if isComplex(T) {
+		a /= 2
+	}
+	if a > s.MaxAlign {
+		return s.MaxAlign
+	}
+	return a
+}
+
+func (s *StdSizes) Offsetsof(fields []*Var) []int64 {
+	offsets := make([]int64, len(fields))
+	var o int64
+	for i, f := range fields {
+		a := s.Alignof(f.typ)
+		o = align(o, a)
+		offsets[i] = o
+		o += s.Sizeof(f.typ)
+	}
+	return offsets
+}
+
+var basicSizes = [...]byte{
+	Bool:       1,
+	Int8:       1,
+	Int16:      2,
+	Int32:      4,
+	Int64:      8,
+	Uint8:      1,
+	Uint16:     2,
+	Uint32:     4,
+	Uint64:     8,
+	Float32:    4,
+	Float64:    8,
+	Complex64:  8,
+	Complex128: 16,
+}
+
+func (s *StdSizes) Sizeof(T Type) int64 {
+	switch t := T.Underlying().(type) {
+	case *Basic:
+		assert(isTyped(T))
+		k := t.kind
+		if int(k) < len(basicSizes) {
+			if s := basicSizes[k]; s > 0 {
+				return int64(s)
+			}
+		}
+		if k == String {
+			return s.WordSize * 2
+		}
+	case *Array:
+		n := t.len
+		if n <= 0 {
+			return 0
+		}
+		// n > 0
+		a := s.Alignof(t.elem)
+		z := s.Sizeof(t.elem)
+		return align(z, a)*(n-1) + z
+	case *Slice:
+		return s.WordSize * 3
+	case *Struct:
+		n := t.NumFields()
+		if n == 0 {
+			return 0
+		}
+		offsets := s.Offsetsof(t.fields)
+		return offsets[n-1] + s.Sizeof(t.fields[n-1].typ)
+	case *Interface:
+		return s.WordSize * 2
+	}
+	return s.WordSize // catch-all
+}
+
+// common architecture word sizes and alignments
+var gcArchSizes = map[string]*StdSizes{
+	"386":      {4, 4},
+	"arm":      {4, 4},
+	"arm64":    {8, 8},
+	"amd64":    {8, 8},
+	"amd64p32": {4, 8},
+	"mips":     {4, 4},
+	"mipsle":   {4, 4},
+	"mips64":   {8, 8},
+	"mips64le": {8, 8},
+	"ppc64":    {8, 8},
+	"ppc64le":  {8, 8},
+	"s390x":    {8, 8},
+	// When adding more architectures here,
+	// update the doc string of SizesFor below.
+}
+
+// SizesFor returns the Sizes used by a compiler for an architecture.
+// The result is nil if a compiler/architecture pair is not known.
+//
+// Supported architectures for compiler "gc":
+// "386", "arm", "arm64", "amd64", "amd64p32", "mips", "mipsle",
+// "mips64", "mips64le", "ppc64", "ppc64le", "s390x".
+func SizesFor(compiler, arch string) Sizes {
+	if compiler != "gc" {
+		return nil
+	}
+	s, ok := gcArchSizes[arch]
+	if !ok {
+		return nil
+	}
+	return s
+}
+
+// stdSizes is used if Config.Sizes == nil.
+var stdSizes = SizesFor("gc", "amd64")
+
+func (conf *Config) alignof(T Type) int64 {
+	if s := conf.Sizes; s != nil {
+		if a := s.Alignof(T); a >= 1 {
+			return a
+		}
+		panic("Config.Sizes.Alignof returned an alignment < 1")
+	}
+	return stdSizes.Alignof(T)
+}
+
+func (conf *Config) offsetsof(T *Struct) []int64 {
+	var offsets []int64
+	if T.NumFields() > 0 {
+		// compute offsets on demand
+		if s := conf.Sizes; s != nil {
+			offsets = s.Offsetsof(T.fields)
+			// sanity checks
+			if len(offsets) != T.NumFields() {
+				panic("Config.Sizes.Offsetsof returned the wrong number of offsets")
+			}
+			for _, o := range offsets {
+				if o < 0 {
+					panic("Config.Sizes.Offsetsof returned an offset < 0")
+				}
+			}
+		} else {
+			offsets = stdSizes.Offsetsof(T.fields)
+		}
+	}
+	return offsets
+}
+
+// offsetof returns the offset of the field specified via
+// the index sequence relative to typ. All embedded fields
+// must be structs (rather than pointer to structs).
+func (conf *Config) offsetof(typ Type, index []int) int64 {
+	var o int64
+	for _, i := range index {
+		s := typ.Underlying().(*Struct)
+		o += conf.offsetsof(s)[i]
+		typ = s.fields[i].typ
+	}
+	return o
+}
+
+func (conf *Config) sizeof(T Type) int64 {
+	if s := conf.Sizes; s != nil {
+		if z := s.Sizeof(T); z >= 0 {
+			return z
+		}
+		panic("Config.Sizes.Sizeof returned a size < 0")
+	}
+	return stdSizes.Sizeof(T)
+}
+
+// align returns the smallest y >= x such that y % a == 0.
+func align(x, a int64) int64 {
+	y := x + a - 1
+	return y - y%a
+}

third_party/forked/golang/go/types/stmt.go

+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements typechecking of statements.
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"sort"
+)
+
+func (check *Checker) funcBody(decl *declInfo, name string, sig *Signature, body *ast.BlockStmt) {
+	if trace {
+		if name == "" {
+			name = "<function literal>"
+		}
+		fmt.Printf("--- %s: %s {\n", name, sig)
+		defer fmt.Println("--- <end>")
+	}
+
+	// set function scope extent
+	sig.scope.pos = body.Pos()
+	sig.scope.end = body.End()
+
+	// save/restore current context and setup function context
+	// (and use 0 indentation at function start)
+	defer func(ctxt context, indent int) {
+		check.context = ctxt
+		check.indent = indent
+	}(check.context, check.indent)
+	check.context = context{
+		decl:  decl,
+		scope: sig.scope,
+		sig:   sig,
+	}
+	check.indent = 0
+
+	check.stmtList(0, body.List)
+
+	if check.hasLabel {
+		check.labels(body)
+	}
+
+	if sig.results.Len() > 0 && !check.isTerminating(body, "") {
+		check.error(body.Rbrace, "missing return")
+	}
+
+	// spec: "Implementation restriction: A compiler may make it illegal to
+	// declare a variable inside a function body if the variable is never used."
+	// (One could check each scope after use, but that distributes this check
+	// over several places because CloseScope is not always called explicitly.)
+	check.usage(sig.scope)
+}
+
+func (check *Checker) usage(scope *Scope) {
+	var unused []*Var
+	for _, elem := range scope.elems {
+		if v, _ := elem.(*Var); v != nil && !v.used {
+			unused = append(unused, v)
+		}
+	}
+	sort.Slice(unused, func(i, j int) bool {
+		return unused[i].pos < unused[j].pos
+	})
+	for _, v := range unused {
+		check.softErrorf(v.pos, "%s declared but not used", v.name)
+	}
+
+	for _, scope := range scope.children {
+		// Don't go inside closure scopes a second time;
+		// they are handled explicitly by funcBody.
+		if !scope.isFunc {
+			check.usage(scope)
+		}
+	}
+}
+
+// stmtContext is a bitset describing which
+// control-flow statements are permissible,
+// and provides additional context information
+// for better error messages.
+type stmtContext uint
+
+const (
+	// permissible control-flow statements
+	breakOk stmtContext = 1 << iota
+	continueOk
+	fallthroughOk
+
+	// additional context information
+	finalSwitchCase
+)
+
+func (check *Checker) simpleStmt(s ast.Stmt) {
+	if s != nil {
+		check.stmt(0, s)
+	}
+}
+
+func trimTrailingEmptyStmts(list []ast.Stmt) []ast.Stmt {
+	for i := len(list); i > 0; i-- {
+		if _, ok := list[i-1].(*ast.EmptyStmt); !ok {
+			return list[:i]
+		}
+	}
+	return nil
+}
+
+func (check *Checker) stmtList(ctxt stmtContext, list []ast.Stmt) {
+	ok := ctxt&fallthroughOk != 0
+	inner := ctxt &^ fallthroughOk
+	list = trimTrailingEmptyStmts(list) // trailing empty statements are "invisible" to fallthrough analysis
+	for i, s := range list {
+		inner := inner
+		if ok && i+1 == len(list) {
+			inner |= fallthroughOk
+		}
+		check.stmt(inner, s)
+	}
+}
+
+func (check *Checker) multipleDefaults(list []ast.Stmt) {
+	var first ast.Stmt
+	for _, s := range list {
+		var d ast.Stmt
+		switch c := s.(type) {
+		case *ast.CaseClause:
+			if len(c.List) == 0 {
+				d = s
+			}
+		case *ast.CommClause:
+			if c.Comm == nil {
+				d = s
+			}
+		default:
+			check.invalidAST(s.Pos(), "case/communication clause expected")
+		}
+		if d != nil {
+			if first != nil {
+				check.errorf(d.Pos(), "multiple defaults (first at %s)", check.fset.Position(first.Pos()))
+			} else {
+				first = d
+			}
+		}
+	}
+}
+
+func (check *Checker) openScope(s ast.Stmt, comment string) {
+	scope := NewScope(check.scope, s.Pos(), s.End(), comment)
+	check.recordScope(s, scope)
+	check.scope = scope
+}
+
+func (check *Checker) closeScope() {
+	check.scope = check.scope.Parent()
+}
+
+func assignOp(op token.Token) token.Token {
+	// token_test.go verifies the token ordering this function relies on
+	if token.ADD_ASSIGN <= op && op <= token.AND_NOT_ASSIGN {
+		return op + (token.ADD - token.ADD_ASSIGN)
+	}
+	return token.ILLEGAL
+}
+
+func (check *Checker) suspendedCall(keyword string, call *ast.CallExpr) {
+	var x operand
+	var msg string
+	switch check.rawExpr(&x, call, nil) {
+	case conversion:
+		msg = "requires function call, not conversion"
+	case expression:
+		msg = "discards result of"
+	case statement:
+		return
+	default:
+		unreachable()
+	}
+	check.errorf(x.pos(), "%s %s %s", keyword, msg, &x)
+}
+
+// goVal returns the Go value for val, or nil.
+func goVal(val constant.Value) interface{} {
+	// val should exist, but be conservative and check
+	if val == nil {
+		return nil
+	}
+	// Match implementation restriction of other compilers.
+	// gc only checks duplicates for integer, floating-point
+	// and string values, so only create Go values for these
+	// types.
+	switch val.Kind() {
+	case constant.Int:
+		if x, ok := constant.Int64Val(val); ok {
+			return x
+		}
+		if x, ok := constant.Uint64Val(val); ok {
+			return x
+		}
+	case constant.Float:
+		if x, ok := constant.Float64Val(val); ok {
+			return x
+		}
+	case constant.String:
+		return constant.StringVal(val)
+	}
+	return nil
+}
+
+// A valueMap maps a case value (of a basic Go type) to a list of positions
+// where the same case value appeared, together with the corresponding case
+// types.
+// Since two case values may have the same "underlying" value but different
+// types we need to also check the value's types (e.g., byte(1) vs myByte(1))
+// when the switch expression is of interface type.
+type (
+	valueMap  map[interface{}][]valueType // underlying Go value -> valueType
+	valueType struct {
+		pos token.Pos
+		typ Type
+	}
+)
+
+func (check *Checker) caseValues(x *operand, values []ast.Expr, seen valueMap) {
+L:
+	for _, e := range values {
+		var v operand
+		check.expr(&v, e)
+		if x.mode == invalid || v.mode == invalid {
+			continue L
+		}
+		check.convertUntyped(&v, x.typ)
+		if v.mode == invalid {
+			continue L
+		}
+		// Order matters: By comparing v against x, error positions are at the case values.
+		res := v // keep original v unchanged
+		check.comparison(&res, x, token.EQL)
+		if res.mode == invalid {
+			continue L
+		}
+		if v.mode != constant_ {
+			continue L // we're done
+		}
+		// look for duplicate values
+		if val := goVal(v.val); val != nil {
+			// look for duplicate types for a given value
+			// (quadratic algorithm, but these lists tend to be very short)
+			for _, vt := range seen[val] {
+				if Identical(v.typ, vt.typ) {
+					check.errorf(v.pos(), "duplicate case %s in expression switch", &v)
+					check.error(vt.pos, "\tprevious case") // secondary error, \t indented
+					continue L
+				}
+			}
+			seen[val] = append(seen[val], valueType{v.pos(), v.typ})
+		}
+	}
+}
+
+func (check *Checker) caseTypes(x *operand, xtyp *Interface, types []ast.Expr, seen map[Type]token.Pos) (T Type) {
+L:
+	for _, e := range types {
+		T = check.typOrNil(e)
+		if T == Typ[Invalid] {
+			continue L
+		}
+		// look for duplicate types
+		// (quadratic algorithm, but type switches tend to be reasonably small)
+		for t, pos := range seen {
+			if T == nil && t == nil || T != nil && t != nil && Identical(T, t) {
+				// talk about "case" rather than "type" because of nil case
+				Ts := "nil"
+				if T != nil {
+					Ts = T.String()
+				}
+				check.errorf(e.Pos(), "duplicate case %s in type switch", Ts)
+				check.error(pos, "\tprevious case") // secondary error, \t indented
+				continue L
+			}
+		}
+		seen[T] = e.Pos()
+		if T != nil {
+			check.typeAssertion(e.Pos(), x, xtyp, T)
+		}
+	}
+	return
+}
+
+// stmt typechecks statement s.
+func (check *Checker) stmt(ctxt stmtContext, s ast.Stmt) {
+	// statements cannot use iota in general
+	// (constant declarations set it explicitly)
+	assert(check.iota == nil)
+
+	// statements must end with the same top scope as they started with
+	if debug {
+		defer func(scope *Scope) {
+			// don't check if code is panicking
+			if p := recover(); p != nil {
+				panic(p)
+			}
+			assert(scope == check.scope)
+		}(check.scope)
+	}
+
+	inner := ctxt &^ (fallthroughOk | finalSwitchCase)
+	switch s := s.(type) {
+	case *ast.BadStmt, *ast.EmptyStmt:
+		// ignore
+
+	case *ast.DeclStmt:
+		check.declStmt(s.Decl)
+
+	case *ast.LabeledStmt:
+		check.hasLabel = true
+		check.stmt(ctxt, s.Stmt)
+
+	case *ast.ExprStmt:
+		// spec: "With the exception of specific built-in functions,
+		// function and method calls and receive operations can appear
+		// in statement context. Such statements may be parenthesized."
+		var x operand
+		kind := check.rawExpr(&x, s.X, nil)
+		var msg string
+		switch x.mode {
+		default:
+			if kind == statement {
+				return
+			}
+			msg = "is not used"
+		case builtin:
+			msg = "must be called"
+		case typexpr:
+			msg = "is not an expression"
+		}
+		check.errorf(x.pos(), "%s %s", &x, msg)
+
+	case *ast.SendStmt:
+		var ch, x operand
+		check.expr(&ch, s.Chan)
+		check.expr(&x, s.Value)
+		if ch.mode == invalid || x.mode == invalid {
+			return
+		}
+
+		tch, ok := ch.typ.Underlying().(*Chan)
+		if !ok {
+			check.invalidOp(s.Arrow, "cannot send to non-chan type %s", ch.typ)
+			return
+		}
+
+		if tch.dir == RecvOnly {
+			check.invalidOp(s.Arrow, "cannot send to receive-only type %s", tch)
+			return
+		}
+
+		check.assignment(&x, tch.elem, "send")
+
+	case *ast.IncDecStmt:
+		var op token.Token
+		switch s.Tok {
+		case token.INC:
+			op = token.ADD
+		case token.DEC:
+			op = token.SUB
+		default:
+			check.invalidAST(s.TokPos, "unknown inc/dec operation %s", s.Tok)
+			return
+		}
+
+		var x operand
+		check.expr(&x, s.X)
+		if x.mode == invalid {
+			return
+		}
+		if !isNumeric(x.typ) {
+			check.invalidOp(s.X.Pos(), "%s%s (non-numeric type %s)", s.X, s.Tok, x.typ)
+			return
+		}
+
+		Y := &ast.BasicLit{ValuePos: s.X.Pos(), Kind: token.INT, Value: "1"} // use x's position
+		check.binary(&x, nil, s.X, Y, op)
+		if x.mode == invalid {
+			return
+		}
+		check.assignVar(s.X, &x)
+
+	case *ast.AssignStmt:
+		switch s.Tok {
+		case token.ASSIGN, token.DEFINE:
+			if len(s.Lhs) == 0 {
+				check.invalidAST(s.Pos(), "missing lhs in assignment")
+				return
+			}
+			if s.Tok == token.DEFINE {
+				check.shortVarDecl(s.TokPos, s.Lhs, s.Rhs)
+			} else {
+				// regular assignment
+				check.assignVars(s.Lhs, s.Rhs)
+			}
+
+		default:
+			// assignment operations
+			if len(s.Lhs) != 1 || len(s.Rhs) != 1 {
+				check.errorf(s.TokPos, "assignment operation %s requires single-valued expressions", s.Tok)
+				return
+			}
+			op := assignOp(s.Tok)
+			if op == token.ILLEGAL {
+				check.invalidAST(s.TokPos, "unknown assignment operation %s", s.Tok)
+				return
+			}
+			var x operand
+			check.binary(&x, nil, s.Lhs[0], s.Rhs[0], op)
+			if x.mode == invalid {
+				return
+			}
+			check.assignVar(s.Lhs[0], &x)
+		}
+
+	case *ast.GoStmt:
+		check.suspendedCall("go", s.Call)
+
+	case *ast.DeferStmt:
+		check.suspendedCall("defer", s.Call)
+
+	case *ast.ReturnStmt:
+		res := check.sig.results
+		if res.Len() > 0 {
+			// function returns results
+			// (if one, say the first, result parameter is named, all of them are named)
+			if len(s.Results) == 0 && res.vars[0].name != "" {
+				// spec: "Implementation restriction: A compiler may disallow an empty expression
+				// list in a "return" statement if a different entity (constant, type, or variable)
+				// with the same name as a result parameter is in scope at the place of the return."
+				for _, obj := range res.vars {
+					if _, alt := check.scope.LookupParent(obj.name, check.pos); alt != nil && alt != obj {
+						check.errorf(s.Pos(), "result parameter %s not in scope at return", obj.name)
+						check.errorf(alt.Pos(), "\tinner declaration of %s", obj)
+						// ok to continue
+					}
+				}
+			} else {
+				// return has results or result parameters are unnamed
+				check.initVars(res.vars, s.Results, s.Return)
+			}
+		} else if len(s.Results) > 0 {
+			check.error(s.Results[0].Pos(), "no result values expected")
+			check.use(s.Results...)
+		}
+
+	case *ast.BranchStmt:
+		if s.Label != nil {
+			check.hasLabel = true
+			return // checked in 2nd pass (check.labels)
+		}
+		switch s.Tok {
+		case token.BREAK:
+			if ctxt&breakOk == 0 {
+				check.error(s.Pos(), "break not in for, switch, or select statement")
+			}
+		case token.CONTINUE:
+			if ctxt&continueOk == 0 {
+				check.error(s.Pos(), "continue not in for statement")
+			}
+		case token.FALLTHROUGH:
+			if ctxt&fallthroughOk == 0 {
+				msg := "fallthrough statement out of place"
+				if ctxt&finalSwitchCase != 0 {
+					msg = "cannot fallthrough final case in switch"
+				}
+				check.error(s.Pos(), msg)
+			}
+		default:
+			check.invalidAST(s.Pos(), "branch statement: %s", s.Tok)
+		}
+
+	case *ast.BlockStmt:
+		check.openScope(s, "block")
+		defer check.closeScope()
+
+		check.stmtList(inner, s.List)
+
+	case *ast.IfStmt:
+		check.openScope(s, "if")
+		defer check.closeScope()
+
+		check.simpleStmt(s.Init)
+		var x operand
+		check.expr(&x, s.Cond)
+		if x.mode != invalid && !isBoolean(x.typ) {
+			check.error(s.Cond.Pos(), "non-boolean condition in if statement")
+		}
+		check.stmt(inner, s.Body)
+		// The parser produces a correct AST but if it was modified
+		// elsewhere the else branch may be invalid. Check again.
+		switch s.Else.(type) {
+		case nil, *ast.BadStmt:
+			// valid or error already reported
+		case *ast.IfStmt, *ast.BlockStmt:
+			check.stmt(inner, s.Else)
+		default:
+			check.error(s.Else.Pos(), "invalid else branch in if statement")
+		}
+
+	case *ast.SwitchStmt:
+		inner |= breakOk
+		check.openScope(s, "switch")
+		defer check.closeScope()
+
+		check.simpleStmt(s.Init)
+		var x operand
+		if s.Tag != nil {
+			check.expr(&x, s.Tag)
+			// By checking assignment of x to an invisible temporary
+			// (as a compiler would), we get all the relevant checks.
+			check.assignment(&x, nil, "switch expression")
+		} else {
+			// spec: "A missing switch expression is
+			// equivalent to the boolean value true."
+			x.mode = constant_
+			x.typ = Typ[Bool]
+			x.val = constant.MakeBool(true)
+			x.expr = &ast.Ident{NamePos: s.Body.Lbrace, Name: "true"}
+		}
+
+		check.multipleDefaults(s.Body.List)
+
+		seen := make(valueMap) // map of seen case values to positions and types
+		for i, c := range s.Body.List {
+			clause, _ := c.(*ast.CaseClause)
+			if clause == nil {
+				check.invalidAST(c.Pos(), "incorrect expression switch case")
+				continue
+			}
+			check.caseValues(&x, clause.List, seen)
+			check.openScope(clause, "case")
+			inner := inner
+			if i+1 < len(s.Body.List) {
+				inner |= fallthroughOk
+			} else {
+				inner |= finalSwitchCase
+			}
+			check.stmtList(inner, clause.Body)
+			check.closeScope()
+		}
+
+	case *ast.TypeSwitchStmt:
+		inner |= breakOk
+		check.openScope(s, "type switch")
+		defer check.closeScope()
+
+		check.simpleStmt(s.Init)
+
+		// A type switch guard must be of the form:
+		//
+		//     TypeSwitchGuard = [ identifier ":=" ] PrimaryExpr "." "(" "type" ")" .
+		//
+		// The parser is checking syntactic correctness;
+		// remaining syntactic errors are considered AST errors here.
+		// TODO(gri) better factoring of error handling (invalid ASTs)
+		//
+		var lhs *ast.Ident // lhs identifier or nil
+		var rhs ast.Expr
+		switch guard := s.Assign.(type) {
+		case *ast.ExprStmt:
+			rhs = guard.X
+		case *ast.AssignStmt:
+			if len(guard.Lhs) != 1 || guard.Tok != token.DEFINE || len(guard.Rhs) != 1 {
+				check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+				return
+			}
+
+			lhs, _ = guard.Lhs[0].(*ast.Ident)
+			if lhs == nil {
+				check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+				return
+			}
+
+			if lhs.Name == "_" {
+				// _ := x.(type) is an invalid short variable declaration
+				check.softErrorf(lhs.Pos(), "no new variable on left side of :=")
+				lhs = nil // avoid declared but not used error below
+			} else {
+				check.recordDef(lhs, nil) // lhs variable is implicitly declared in each cause clause
+			}
+
+			rhs = guard.Rhs[0]
+
+		default:
+			check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+			return
+		}
+
+		// rhs must be of the form: expr.(type) and expr must be an interface
+		expr, _ := rhs.(*ast.TypeAssertExpr)
+		if expr == nil || expr.Type != nil {
+			check.invalidAST(s.Pos(), "incorrect form of type switch guard")
+			return
+		}
+		var x operand
+		check.expr(&x, expr.X)
+		if x.mode == invalid {
+			return
+		}
+		xtyp, _ := x.typ.Underlying().(*Interface)
+		if xtyp == nil {
+			check.errorf(x.pos(), "%s is not an interface", &x)
+			return
+		}
+
+		check.multipleDefaults(s.Body.List)
+
+		var lhsVars []*Var               // list of implicitly declared lhs variables
+		seen := make(map[Type]token.Pos) // map of seen types to positions
+		for _, s := range s.Body.List {
+			clause, _ := s.(*ast.CaseClause)
+			if clause == nil {
+				check.invalidAST(s.Pos(), "incorrect type switch case")
+				continue
+			}
+			// Check each type in this type switch case.
+			T := check.caseTypes(&x, xtyp, clause.List, seen)
+			check.openScope(clause, "case")
+			// If lhs exists, declare a corresponding variable in the case-local scope.
+			if lhs != nil {
+				// spec: "The TypeSwitchGuard may include a short variable declaration.
+				// When that form is used, the variable is declared at the beginning of
+				// the implicit block in each clause. In clauses with a case listing
+				// exactly one type, the variable has that type; otherwise, the variable
+				// has the type of the expression in the TypeSwitchGuard."
+				if len(clause.List) != 1 || T == nil {
+					T = x.typ
+				}
+				obj := NewVar(lhs.Pos(), check.pkg, lhs.Name, T)
+				scopePos := clause.Pos() + token.Pos(len("default")) // for default clause (len(List) == 0)
+				if n := len(clause.List); n > 0 {
+					scopePos = clause.List[n-1].End()
+				}
+				check.declare(check.scope, nil, obj, scopePos)
+				check.recordImplicit(clause, obj)
+				// For the "declared but not used" error, all lhs variables act as
+				// one; i.e., if any one of them is 'used', all of them are 'used'.
+				// Collect them for later analysis.
+				lhsVars = append(lhsVars, obj)
+			}
+			check.stmtList(inner, clause.Body)
+			check.closeScope()
+		}
+
+		// If lhs exists, we must have at least one lhs variable that was used.
+		if lhs != nil {
+			var used bool
+			for _, v := range lhsVars {
+				if v.used {
+					used = true
+				}
+				v.used = true // avoid usage error when checking entire function
+			}
+			if !used {
+				check.softErrorf(lhs.Pos(), "%s declared but not used", lhs.Name)
+			}
+		}
+
+	case *ast.SelectStmt:
+		inner |= breakOk
+
+		check.multipleDefaults(s.Body.List)
+
+		for _, s := range s.Body.List {
+			clause, _ := s.(*ast.CommClause)
+			if clause == nil {
+				continue // error reported before
+			}
+
+			// clause.Comm must be a SendStmt, RecvStmt, or default case
+			valid := false
+			var rhs ast.Expr // rhs of RecvStmt, or nil
+			switch s := clause.Comm.(type) {
+			case nil, *ast.SendStmt:
+				valid = true
+			case *ast.AssignStmt:
+				if len(s.Rhs) == 1 {
+					rhs = s.Rhs[0]
+				}
+			case *ast.ExprStmt:
+				rhs = s.X
+			}
+
+			// if present, rhs must be a receive operation
+			if rhs != nil {
+				if x, _ := unparen(rhs).(*ast.UnaryExpr); x != nil && x.Op == token.ARROW {
+					valid = true
+				}
+			}
+
+			if !valid {
+				check.error(clause.Comm.Pos(), "select case must be send or receive (possibly with assignment)")
+				continue
+			}
+
+			check.openScope(s, "case")
+			if clause.Comm != nil {
+				check.stmt(inner, clause.Comm)
+			}
+			check.stmtList(inner, clause.Body)
+			check.closeScope()
+		}
+
+	case *ast.ForStmt:
+		inner |= breakOk | continueOk
+		check.openScope(s, "for")
+		defer check.closeScope()
+
+		check.simpleStmt(s.Init)
+		if s.Cond != nil {
+			var x operand
+			check.expr(&x, s.Cond)
+			if x.mode != invalid && !isBoolean(x.typ) {
+				check.error(s.Cond.Pos(), "non-boolean condition in for statement")
+			}
+		}
+		check.simpleStmt(s.Post)
+		// spec: "The init statement may be a short variable
+		// declaration, but the post statement must not."
+		if s, _ := s.Post.(*ast.AssignStmt); s != nil && s.Tok == token.DEFINE {
+			check.softErrorf(s.Pos(), "cannot declare in post statement")
+			// Don't call useLHS here because we want to use the lhs in
+			// this erroneous statement so that we don't get errors about
+			// these lhs variables being declared but not used.
+			check.use(s.Lhs...) // avoid follow-up errors
+		}
+		check.stmt(inner, s.Body)
+
+	case *ast.RangeStmt:
+		inner |= breakOk | continueOk
+		check.openScope(s, "for")
+		defer check.closeScope()
+
+		// check expression to iterate over
+		var x operand
+		check.expr(&x, s.X)
+
+		// determine key/value types
+		var key, val Type
+		if x.mode != invalid {
+			switch typ := x.typ.Underlying().(type) {
+			case *Basic:
+				if isString(typ) {
+					key = Typ[Int]
+					val = universeRune // use 'rune' name
+				}
+			case *Array:
+				key = Typ[Int]
+				val = typ.elem
+			case *Slice:
+				key = Typ[Int]
+				val = typ.elem
+			case *Pointer:
+				if typ, _ := typ.base.Underlying().(*Array); typ != nil {
+					key = Typ[Int]
+					val = typ.elem
+				}
+			case *Map:
+				key = typ.key
+				val = typ.elem
+			case *Chan:
+				key = typ.elem
+				val = Typ[Invalid]
+				if typ.dir == SendOnly {
+					check.errorf(x.pos(), "cannot range over send-only channel %s", &x)
+					// ok to continue
+				}
+				if s.Value != nil {
+					check.errorf(s.Value.Pos(), "iteration over %s permits only one iteration variable", &x)
+					// ok to continue
+				}
+			}
+		}
+
+		if key == nil {
+			check.errorf(x.pos(), "cannot range over %s", &x)
+			// ok to continue
+		}
+
+		// check assignment to/declaration of iteration variables
+		// (irregular assignment, cannot easily map to existing assignment checks)
+
+		// lhs expressions and initialization value (rhs) types
+		lhs := [2]ast.Expr{s.Key, s.Value}
+		rhs := [2]Type{key, val} // key, val may be nil
+
+		if s.Tok == token.DEFINE {
+			// short variable declaration; variable scope starts after the range clause
+			// (the for loop opens a new scope, so variables on the lhs never redeclare
+			// previously declared variables)
+			var vars []*Var
+			for i, lhs := range lhs {
+				if lhs == nil {
+					continue
+				}
+
+				// determine lhs variable
+				var obj *Var
+				if ident, _ := lhs.(*ast.Ident); ident != nil {
+					// declare new variable
+					name := ident.Name
+					obj = NewVar(ident.Pos(), check.pkg, name, nil)
+					check.recordDef(ident, obj)
+					// _ variables don't count as new variables
+					if name != "_" {
+						vars = append(vars, obj)
+					}
+				} else {
+					check.errorf(lhs.Pos(), "cannot declare %s", lhs)
+					obj = NewVar(lhs.Pos(), check.pkg, "_", nil) // dummy variable
+				}
+
+				// initialize lhs variable
+				if typ := rhs[i]; typ != nil {
+					x.mode = value
+					x.expr = lhs // we don't have a better rhs expression to use here
+					x.typ = typ
+					check.initVar(obj, &x, "range clause")
+				} else {
+					obj.typ = Typ[Invalid]
+					obj.used = true // don't complain about unused variable
+				}
+			}
+
+			// declare variables
+			if len(vars) > 0 {
+				scopePos := s.X.End()
+				for _, obj := range vars {
+					// spec: "The scope of a constant or variable identifier declared inside
+					// a function begins at the end of the ConstSpec or VarSpec (ShortVarDecl
+					// for short variable declarations) and ends at the end of the innermost
+					// containing block."
+					check.declare(check.scope, nil /* recordDef already called */, obj, scopePos)
+				}
+			} else {
+				check.error(s.TokPos, "no new variables on left side of :=")
+			}
+		} else {
+			// ordinary assignment
+			for i, lhs := range lhs {
+				if lhs == nil {
+					continue
+				}
+				if typ := rhs[i]; typ != nil {
+					x.mode = value
+					x.expr = lhs // we don't have a better rhs expression to use here
+					x.typ = typ
+					check.assignVar(lhs, &x)
+				}
+			}
+		}
+
+		check.stmt(inner, s.Body)
+
+	default:
+		check.error(s.Pos(), "invalid statement")
+	}
+}

third_party/forked/golang/go/types/type.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import "sort"
+
+// A Type represents a type of Go.
+// All types implement the Type interface.
+type Type interface {
+	// Underlying returns the underlying type of a type.
+	Underlying() Type
+
+	// String returns a string representation of a type.
+	String() string
+}
+
+// BasicKind describes the kind of basic type.
+type BasicKind int
+
+const (
+	Invalid BasicKind = iota // type is invalid
+
+	// predeclared types
+	Bool
+	Int
+	Int8
+	Int16
+	Int32
+	Int64
+	Uint
+	Uint8
+	Uint16
+	Uint32
+	Uint64
+	Uintptr
+	Float32
+	Float64
+	Complex64
+	Complex128
+	String
+	UnsafePointer
+
+	// types for untyped values
+	UntypedBool
+	UntypedInt
+	UntypedRune
+	UntypedFloat
+	UntypedComplex
+	UntypedString
+	UntypedNil
+
+	// aliases
+	Byte = Uint8
+	Rune = Int32
+)
+
+// BasicInfo is a set of flags describing properties of a basic type.
+type BasicInfo int
+
+// Properties of basic types.
+const (
+	IsBoolean BasicInfo = 1 << iota
+	IsInteger
+	IsUnsigned
+	IsFloat
+	IsComplex
+	IsString
+	IsUntyped
+
+	IsOrdered   = IsInteger | IsFloat | IsString
+	IsNumeric   = IsInteger | IsFloat | IsComplex
+	IsConstType = IsBoolean | IsNumeric | IsString
+)
+
+// A Basic represents a basic type.
+type Basic struct {
+	kind BasicKind
+	info BasicInfo
+	name string
+}
+
+// Kind returns the kind of basic type b.
+func (b *Basic) Kind() BasicKind { return b.kind }
+
+// Info returns information about properties of basic type b.
+func (b *Basic) Info() BasicInfo { return b.info }
+
+// Name returns the name of basic type b.
+func (b *Basic) Name() string { return b.name }
+
+// An Array represents an array type.
+type Array struct {
+	len  int64
+	elem Type
+}
+
+// NewArray returns a new array type for the given element type and length.
+// A negative length indicates an unknown length.
+func NewArray(elem Type, len int64) *Array { return &Array{len, elem} }
+
+// Len returns the length of array a.
+// A negative result indicates an unknown length.
+func (a *Array) Len() int64 { return a.len }
+
+// Elem returns element type of array a.
+func (a *Array) Elem() Type { return a.elem }
+
+// A Slice represents a slice type.
+type Slice struct {
+	elem Type
+}
+
+// NewSlice returns a new slice type for the given element type.
+func NewSlice(elem Type) *Slice { return &Slice{elem} }
+
+// Elem returns the element type of slice s.
+func (s *Slice) Elem() Type { return s.elem }
+
+// A Struct represents a struct type.
+type Struct struct {
+	fields []*Var
+	tags   []string // field tags; nil if there are no tags
+}
+
+// NewStruct returns a new struct with the given fields and corresponding field tags.
+// If a field with index i has a tag, tags[i] must be that tag, but len(tags) may be
+// only as long as required to hold the tag with the largest index i. Consequently,
+// if no field has a tag, tags may be nil.
+func NewStruct(fields []*Var, tags []string) *Struct {
+	var fset objset
+	for _, f := range fields {
+		if f.name != "_" && fset.insert(f) != nil {
+			panic("multiple fields with the same name")
+		}
+	}
+	if len(tags) > len(fields) {
+		panic("more tags than fields")
+	}
+	return &Struct{fields: fields, tags: tags}
+}
+
+// NumFields returns the number of fields in the struct (including blank and anonymous fields).
+func (s *Struct) NumFields() int { return len(s.fields) }
+
+// Field returns the i'th field for 0 <= i < NumFields().
+func (s *Struct) Field(i int) *Var { return s.fields[i] }
+
+// Tag returns the i'th field tag for 0 <= i < NumFields().
+func (s *Struct) Tag(i int) string {
+	if i < len(s.tags) {
+		return s.tags[i]
+	}
+	return ""
+}
+
+// A Pointer represents a pointer type.
+type Pointer struct {
+	base Type // element type
+}
+
+// NewPointer returns a new pointer type for the given element (base) type.
+func NewPointer(elem Type) *Pointer { return &Pointer{base: elem} }
+
+// Elem returns the element type for the given pointer p.
+func (p *Pointer) Elem() Type { return p.base }
+
+// A Tuple represents an ordered list of variables; a nil *Tuple is a valid (empty) tuple.
+// Tuples are used as components of signatures and to represent the type of multiple
+// assignments; they are not first class types of Go.
+type Tuple struct {
+	vars []*Var
+}
+
+// NewTuple returns a new tuple for the given variables.
+func NewTuple(x ...*Var) *Tuple {
+	if len(x) > 0 {
+		return &Tuple{x}
+	}
+	return nil
+}
+
+// Len returns the number variables of tuple t.
+func (t *Tuple) Len() int {
+	if t != nil {
+		return len(t.vars)
+	}
+	return 0
+}
+
+// At returns the i'th variable of tuple t.
+func (t *Tuple) At(i int) *Var { return t.vars[i] }
+
+// A Signature represents a (non-builtin) function or method type.
+// The receiver is ignored when comparing signatures for identity.
+type Signature struct {
+	// We need to keep the scope in Signature (rather than passing it around
+	// and store it in the Func Object) because when type-checking a function
+	// literal we call the general type checker which returns a general Type.
+	// We then unpack the *Signature and use the scope for the literal body.
+	scope    *Scope // function scope, present for package-local signatures
+	recv     *Var   // nil if not a method
+	params   *Tuple // (incoming) parameters from left to right; or nil
+	results  *Tuple // (outgoing) results from left to right; or nil
+	variadic bool   // true if the last parameter's type is of the form ...T (or string, for append built-in only)
+}
+
+// NewSignature returns a new function type for the given receiver, parameters,
+// and results, either of which may be nil. If variadic is set, the function
+// is variadic, it must have at least one parameter, and the last parameter
+// must be of unnamed slice type.
+func NewSignature(recv *Var, params, results *Tuple, variadic bool) *Signature {
+	if variadic {
+		n := params.Len()
+		if n == 0 {
+			panic("types.NewSignature: variadic function must have at least one parameter")
+		}
+		if _, ok := params.At(n - 1).typ.(*Slice); !ok {
+			panic("types.NewSignature: variadic parameter must be of unnamed slice type")
+		}
+	}
+	return &Signature{nil, recv, params, results, variadic}
+}
+
+// Recv returns the receiver of signature s (if a method), or nil if a
+// function. It is ignored when comparing signatures for identity.
+//
+// For an abstract method, Recv returns the enclosing interface either
+// as a *Named or an *Interface. Due to embedding, an interface may
+// contain methods whose receiver type is a different interface.
+func (s *Signature) Recv() *Var { return s.recv }
+
+// Params returns the parameters of signature s, or nil.
+func (s *Signature) Params() *Tuple { return s.params }
+
+// Results returns the results of signature s, or nil.
+func (s *Signature) Results() *Tuple { return s.results }
+
+// Variadic reports whether the signature s is variadic.
+func (s *Signature) Variadic() bool { return s.variadic }
+
+// An Interface represents an interface type.
+type Interface struct {
+	methods   []*Func  // ordered list of explicitly declared methods
+	embeddeds []*Named // ordered list of explicitly embedded types
+
+	allMethods []*Func // ordered list of methods declared with or embedded in this interface (TODO(gri): replace with mset)
+}
+
+// emptyInterface represents the empty (completed) interface
+var emptyInterface = Interface{allMethods: markComplete}
+
+// markComplete is used to mark an empty interface as completely
+// set up by setting the allMethods field to a non-nil empty slice.
+var markComplete = make([]*Func, 0)
+
+// NewInterface returns a new (incomplete) interface for the given methods and embedded types.
+// To compute the method set of the interface, Complete must be called.
+func NewInterface(methods []*Func, embeddeds []*Named) *Interface {
+	typ := new(Interface)
+
+	if len(methods) == 0 && len(embeddeds) == 0 {
+		return typ
+	}
+
+	var mset objset
+	for _, m := range methods {
+		if mset.insert(m) != nil {
+			panic("multiple methods with the same name")
+		}
+		// set receiver
+		// TODO(gri) Ideally, we should use a named type here instead of
+		// typ, for less verbose printing of interface method signatures.
+		m.typ.(*Signature).recv = NewVar(m.pos, m.pkg, "", typ)
+	}
+	sort.Sort(byUniqueMethodName(methods))
+
+	if embeddeds != nil {
+		sort.Sort(byUniqueTypeName(embeddeds))
+	}
+
+	typ.methods = methods
+	typ.embeddeds = embeddeds
+	return typ
+}
+
+// NumExplicitMethods returns the number of explicitly declared methods of interface t.
+func (t *Interface) NumExplicitMethods() int { return len(t.methods) }
+
+// ExplicitMethod returns the i'th explicitly declared method of interface t for 0 <= i < t.NumExplicitMethods().
+// The methods are ordered by their unique Id.
+func (t *Interface) ExplicitMethod(i int) *Func { return t.methods[i] }
+
+// NumEmbeddeds returns the number of embedded types in interface t.
+func (t *Interface) NumEmbeddeds() int { return len(t.embeddeds) }
+
+// Embedded returns the i'th embedded type of interface t for 0 <= i < t.NumEmbeddeds().
+// The types are ordered by the corresponding TypeName's unique Id.
+func (t *Interface) Embedded(i int) *Named { return t.embeddeds[i] }
+
+// NumMethods returns the total number of methods of interface t.
+func (t *Interface) NumMethods() int { return len(t.allMethods) }
+
+// Method returns the i'th method of interface t for 0 <= i < t.NumMethods().
+// The methods are ordered by their unique Id.
+func (t *Interface) Method(i int) *Func { return t.allMethods[i] }
+
+// Empty returns true if t is the empty interface.
+func (t *Interface) Empty() bool { return len(t.allMethods) == 0 }
+
+// Complete computes the interface's method set. It must be called by users of
+// NewInterface after the interface's embedded types are fully defined and
+// before using the interface type in any way other than to form other types.
+// Complete returns the receiver.
+func (t *Interface) Complete() *Interface {
+	if t.allMethods != nil {
+		return t
+	}
+
+	var allMethods []*Func
+	if t.embeddeds == nil {
+		if t.methods == nil {
+			allMethods = make([]*Func, 0, 1)
+		} else {
+			allMethods = t.methods
+		}
+	} else {
+		allMethods = append(allMethods, t.methods...)
+		for _, et := range t.embeddeds {
+			it := et.Underlying().(*Interface)
+			it.Complete()
+			for _, tm := range it.allMethods {
+				// Make a copy of the method and adjust its receiver type.
+				newm := *tm
+				newmtyp := *tm.typ.(*Signature)
+				newm.typ = &newmtyp
+				newmtyp.recv = NewVar(newm.pos, newm.pkg, "", t)
+				allMethods = append(allMethods, &newm)
+			}
+		}
+		sort.Sort(byUniqueMethodName(allMethods))
+	}
+	t.allMethods = allMethods
+
+	return t
+}
+
+// A Map represents a map type.
+type Map struct {
+	key, elem Type
+}
+
+// NewMap returns a new map for the given key and element types.
+func NewMap(key, elem Type) *Map {
+	return &Map{key, elem}
+}
+
+// Key returns the key type of map m.
+func (m *Map) Key() Type { return m.key }
+
+// Elem returns the element type of map m.
+func (m *Map) Elem() Type { return m.elem }
+
+// A Chan represents a channel type.
+type Chan struct {
+	dir  ChanDir
+	elem Type
+}
+
+// A ChanDir value indicates a channel direction.
+type ChanDir int
+
+// The direction of a channel is indicated by one of these constants.
+const (
+	SendRecv ChanDir = iota
+	SendOnly
+	RecvOnly
+)
+
+// NewChan returns a new channel type for the given direction and element type.
+func NewChan(dir ChanDir, elem Type) *Chan {
+	return &Chan{dir, elem}
+}
+
+// Dir returns the direction of channel c.
+func (c *Chan) Dir() ChanDir { return c.dir }
+
+// Elem returns the element type of channel c.
+func (c *Chan) Elem() Type { return c.elem }
+
+// A Named represents a named type.
+type Named struct {
+	obj        *TypeName // corresponding declared object
+	underlying Type      // possibly a *Named during setup; never a *Named once set up completely
+	methods    []*Func   // methods declared for this type (not the method set of this type)
+}
+
+// NewNamed returns a new named type for the given type name, underlying type, and associated methods.
+// If the given type name obj doesn't have a type yet, its type is set to the returned named type.
+// The underlying type must not be a *Named.
+func NewNamed(obj *TypeName, underlying Type, methods []*Func) *Named {
+	if _, ok := underlying.(*Named); ok {
+		panic("types.NewNamed: underlying type must not be *Named")
+	}
+	typ := &Named{obj: obj, underlying: underlying, methods: methods}
+	if obj.typ == nil {
+		obj.typ = typ
+	}
+	return typ
+}
+
+// Obj returns the type name for the named type t.
+func (t *Named) Obj() *TypeName { return t.obj }
+
+// NumMethods returns the number of explicit methods whose receiver is named type t.
+func (t *Named) NumMethods() int { return len(t.methods) }
+
+// Method returns the i'th method of named type t for 0 <= i < t.NumMethods().
+func (t *Named) Method(i int) *Func { return t.methods[i] }
+
+// SetUnderlying sets the underlying type and marks t as complete.
+func (t *Named) SetUnderlying(underlying Type) {
+	if underlying == nil {
+		panic("types.Named.SetUnderlying: underlying type must not be nil")
+	}
+	if _, ok := underlying.(*Named); ok {
+		panic("types.Named.SetUnderlying: underlying type must not be *Named")
+	}
+	t.underlying = underlying
+}
+
+// AddMethod adds method m unless it is already in the method list.
+func (t *Named) AddMethod(m *Func) {
+	if i, _ := lookupMethod(t.methods, m.pkg, m.name); i < 0 {
+		t.methods = append(t.methods, m)
+	}
+}
+
+// Implementations for Type methods.
+
+func (t *Basic) Underlying() Type     { return t }
+func (t *Array) Underlying() Type     { return t }
+func (t *Slice) Underlying() Type     { return t }
+func (t *Struct) Underlying() Type    { return t }
+func (t *Pointer) Underlying() Type   { return t }
+func (t *Tuple) Underlying() Type     { return t }
+func (t *Signature) Underlying() Type { return t }
+func (t *Interface) Underlying() Type { return t }
+func (t *Map) Underlying() Type       { return t }
+func (t *Chan) Underlying() Type      { return t }
+func (t *Named) Underlying() Type     { return t.underlying }
+
+func (t *Basic) String() string     { return TypeString(t, nil) }
+func (t *Array) String() string     { return TypeString(t, nil) }
+func (t *Slice) String() string     { return TypeString(t, nil) }
+func (t *Struct) String() string    { return TypeString(t, nil) }
+func (t *Pointer) String() string   { return TypeString(t, nil) }
+func (t *Tuple) String() string     { return TypeString(t, nil) }
+func (t *Signature) String() string { return TypeString(t, nil) }
+func (t *Interface) String() string { return TypeString(t, nil) }
+func (t *Map) String() string       { return TypeString(t, nil) }
+func (t *Chan) String() string      { return TypeString(t, nil) }
+func (t *Named) String() string     { return TypeString(t, nil) }

third_party/forked/golang/go/types/typestring.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements printing of types.
+
+package types
+
+import (
+	"bytes"
+	"fmt"
+)
+
+// A Qualifier controls how named package-level objects are printed in
+// calls to TypeString, ObjectString, and SelectionString.
+//
+// These three formatting routines call the Qualifier for each
+// package-level object O, and if the Qualifier returns a non-empty
+// string p, the object is printed in the form p.O.
+// If it returns an empty string, only the object name O is printed.
+//
+// Using a nil Qualifier is equivalent to using (*Package).Path: the
+// object is qualified by the import path, e.g., "encoding/json.Marshal".
+//
+type Qualifier func(*Package) string
+
+// RelativeTo(pkg) returns a Qualifier that fully qualifies members of
+// all packages other than pkg.
+func RelativeTo(pkg *Package) Qualifier {
+	if pkg == nil {
+		return nil
+	}
+	return func(other *Package) string {
+		if pkg == other {
+			return "" // same package; unqualified
+		}
+		return other.Path()
+	}
+}
+
+// If gcCompatibilityMode is set, printing of types is modified
+// to match the representation of some types in the gc compiler:
+//
+//	- byte and rune lose their alias name and simply stand for
+//	  uint8 and int32 respectively
+//	- embedded interfaces get flattened (the embedding info is lost,
+//	  and certain recursive interface types cannot be printed anymore)
+//
+// This makes it easier to compare packages computed with the type-
+// checker vs packages imported from gc export data.
+//
+// Caution: This flag affects all uses of WriteType, globally.
+// It is only provided for testing in conjunction with
+// gc-generated data.
+//
+// This flag is exported in the x/tools/go/types package. We don't
+// need it at the moment in the std repo and so we don't export it
+// anymore. We should eventually try to remove it altogether.
+// TODO(gri) remove this
+var gcCompatibilityMode bool
+
+// TypeString returns the string representation of typ.
+// The Qualifier controls the printing of
+// package-level objects, and may be nil.
+func TypeString(typ Type, qf Qualifier) string {
+	var buf bytes.Buffer
+	WriteType(&buf, typ, qf)
+	return buf.String()
+}
+
+// WriteType writes the string representation of typ to buf.
+// The Qualifier controls the printing of
+// package-level objects, and may be nil.
+func WriteType(buf *bytes.Buffer, typ Type, qf Qualifier) {
+	writeType(buf, typ, qf, make([]Type, 0, 8))
+}
+
+func writeType(buf *bytes.Buffer, typ Type, qf Qualifier, visited []Type) {
+	// Theoretically, this is a quadratic lookup algorithm, but in
+	// practice deeply nested composite types with unnamed component
+	// types are uncommon. This code is likely more efficient than
+	// using a map.
+	for _, t := range visited {
+		if t == typ {
+			fmt.Fprintf(buf, "○%T", typ) // cycle to typ
+			return
+		}
+	}
+	visited = append(visited, typ)
+
+	switch t := typ.(type) {
+	case nil:
+		buf.WriteString("<nil>")
+
+	case *Basic:
+		if t.kind == UnsafePointer {
+			buf.WriteString("unsafe.")
+		}
+		if gcCompatibilityMode {
+			// forget the alias names
+			switch t.kind {
+			case Byte:
+				t = Typ[Uint8]
+			case Rune:
+				t = Typ[Int32]
+			}
+		}
+		buf.WriteString(t.name)
+
+	case *Array:
+		fmt.Fprintf(buf, "[%d]", t.len)
+		writeType(buf, t.elem, qf, visited)
+
+	case *Slice:
+		buf.WriteString("[]")
+		writeType(buf, t.elem, qf, visited)
+
+	case *Struct:
+		buf.WriteString("struct{")
+		for i, f := range t.fields {
+			if i > 0 {
+				buf.WriteString("; ")
+			}
+			if !f.anonymous {
+				buf.WriteString(f.name)
+				buf.WriteByte(' ')
+			}
+			writeType(buf, f.typ, qf, visited)
+			if tag := t.Tag(i); tag != "" {
+				fmt.Fprintf(buf, " %q", tag)
+			}
+		}
+		buf.WriteByte('}')
+
+	case *Pointer:
+		buf.WriteByte('*')
+		writeType(buf, t.base, qf, visited)
+
+	case *Tuple:
+		writeTuple(buf, t, false, qf, visited)
+
+	case *Signature:
+		buf.WriteString("func")
+		writeSignature(buf, t, qf, visited)
+
+	case *Interface:
+		// We write the source-level methods and embedded types rather
+		// than the actual method set since resolved method signatures
+		// may have non-printable cycles if parameters have anonymous
+		// interface types that (directly or indirectly) embed the
+		// current interface. For instance, consider the result type
+		// of m:
+		//
+		//     type T interface{
+		//         m() interface{ T }
+		//     }
+		//
+		buf.WriteString("interface{")
+		empty := true
+		if gcCompatibilityMode {
+			// print flattened interface
+			// (useful to compare against gc-generated interfaces)
+			for i, m := range t.allMethods {
+				if i > 0 {
+					buf.WriteString("; ")
+				}
+				buf.WriteString(m.name)
+				writeSignature(buf, m.typ.(*Signature), qf, visited)
+				empty = false
+			}
+		} else {
+			// print explicit interface methods and embedded types
+			for i, m := range t.methods {
+				if i > 0 {
+					buf.WriteString("; ")
+				}
+				buf.WriteString(m.name)
+				writeSignature(buf, m.typ.(*Signature), qf, visited)
+				empty = false
+			}
+			for i, typ := range t.embeddeds {
+				if i > 0 || len(t.methods) > 0 {
+					buf.WriteString("; ")
+				}
+				writeType(buf, typ, qf, visited)
+				empty = false
+			}
+		}
+		if t.allMethods == nil || len(t.methods) > len(t.allMethods) {
+			if !empty {
+				buf.WriteByte(' ')
+			}
+			buf.WriteString("/* incomplete */")
+		}
+		buf.WriteByte('}')
+
+	case *Map:
+		buf.WriteString("map[")
+		writeType(buf, t.key, qf, visited)
+		buf.WriteByte(']')
+		writeType(buf, t.elem, qf, visited)
+
+	case *Chan:
+		var s string
+		var parens bool
+		switch t.dir {
+		case SendRecv:
+			s = "chan "
+			// chan (<-chan T) requires parentheses
+			if c, _ := t.elem.(*Chan); c != nil && c.dir == RecvOnly {
+				parens = true
+			}
+		case SendOnly:
+			s = "chan<- "
+		case RecvOnly:
+			s = "<-chan "
+		default:
+			panic("unreachable")
+		}
+		buf.WriteString(s)
+		if parens {
+			buf.WriteByte('(')
+		}
+		writeType(buf, t.elem, qf, visited)
+		if parens {
+			buf.WriteByte(')')
+		}
+
+	case *Named:
+		s := "<Named w/o object>"
+		if obj := t.obj; obj != nil {
+			if obj.pkg != nil {
+				writePackage(buf, obj.pkg, qf)
+			}
+			// TODO(gri): function-local named types should be displayed
+			// differently from named types at package level to avoid
+			// ambiguity.
+			s = obj.name
+		}
+		buf.WriteString(s)
+
+	default:
+		// For externally defined implementations of Type.
+		buf.WriteString(t.String())
+	}
+}
+
+func writeTuple(buf *bytes.Buffer, tup *Tuple, variadic bool, qf Qualifier, visited []Type) {
+	buf.WriteByte('(')
+	if tup != nil {
+		for i, v := range tup.vars {
+			if i > 0 {
+				buf.WriteString(", ")
+			}
+			if v.name != "" {
+				buf.WriteString(v.name)
+				buf.WriteByte(' ')
+			}
+			typ := v.typ
+			if variadic && i == len(tup.vars)-1 {
+				if s, ok := typ.(*Slice); ok {
+					buf.WriteString("...")
+					typ = s.elem
+				} else {
+					// special case:
+					// append(s, "foo"...) leads to signature func([]byte, string...)
+					if t, ok := typ.Underlying().(*Basic); !ok || t.kind != String {
+						panic("internal error: string type expected")
+					}
+					writeType(buf, typ, qf, visited)
+					buf.WriteString("...")
+					continue
+				}
+			}
+			writeType(buf, typ, qf, visited)
+		}
+	}
+	buf.WriteByte(')')
+}
+
+// WriteSignature writes the representation of the signature sig to buf,
+// without a leading "func" keyword.
+// The Qualifier controls the printing of
+// package-level objects, and may be nil.
+func WriteSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier) {
+	writeSignature(buf, sig, qf, make([]Type, 0, 8))
+}
+
+func writeSignature(buf *bytes.Buffer, sig *Signature, qf Qualifier, visited []Type) {
+	writeTuple(buf, sig.params, sig.variadic, qf, visited)
+
+	n := sig.results.Len()
+	if n == 0 {
+		// no result
+		return
+	}
+
+	buf.WriteByte(' ')
+	if n == 1 && sig.results.vars[0].name == "" {
+		// single unnamed result
+		writeType(buf, sig.results.vars[0].typ, qf, visited)
+		return
+	}
+
+	// multiple or named result(s)
+	writeTuple(buf, sig.results, false, qf, visited)
+}

third_party/forked/golang/go/types/typexpr.go

+// Copyright 2013 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements type-checking of identifiers and type expressions.
+
+package types
+
+import (
+	"go/ast"
+	"go/constant"
+	"go/token"
+	"sort"
+	"strconv"
+)
+
+// ident type-checks identifier e and initializes x with the value or type of e.
+// If an error occurred, x.mode is set to invalid.
+// For the meaning of def and path, see check.typ, below.
+//
+func (check *Checker) ident(x *operand, e *ast.Ident, def *Named, path []*TypeName) {
+	x.mode = invalid
+	x.expr = e
+
+	scope, obj := check.scope.LookupParent(e.Name, check.pos)
+	if obj == nil {
+		if e.Name == "_" {
+			check.errorf(e.Pos(), "cannot use _ as value or type")
+		} else {
+			check.errorf(e.Pos(), "undeclared name: %s", e.Name)
+		}
+		return
+	}
+	check.recordUse(e, obj)
+
+	check.objDecl(obj, def, path)
+	typ := obj.Type()
+	assert(typ != nil)
+
+	// The object may be dot-imported: If so, remove its package from
+	// the map of unused dot imports for the respective file scope.
+	// (This code is only needed for dot-imports. Without them,
+	// we only have to mark variables, see *Var case below).
+	if pkg := obj.Pkg(); pkg != check.pkg && pkg != nil {
+		delete(check.unusedDotImports[scope], pkg)
+	}
+
+	switch obj := obj.(type) {
+	case *PkgName:
+		check.errorf(e.Pos(), "use of package %s not in selector", obj.name)
+		return
+
+	case *Const:
+		check.addDeclDep(obj)
+		if typ == Typ[Invalid] {
+			return
+		}
+		if obj == universeIota {
+			if check.iota == nil {
+				check.errorf(e.Pos(), "cannot use iota outside constant declaration")
+				return
+			}
+			x.val = check.iota
+		} else {
+			x.val = obj.val
+		}
+		assert(x.val != nil)
+		x.mode = constant_
+
+	case *TypeName:
+		x.mode = typexpr
+		// check for cycle
+		// (it's ok to iterate forward because each named type appears at most once in path)
+		for i, prev := range path {
+			if prev == obj {
+				check.errorf(obj.pos, "illegal cycle in declaration of %s", obj.name)
+				// print cycle
+				for _, obj := range path[i:] {
+					check.errorf(obj.Pos(), "\t%s refers to", obj.Name()) // secondary error, \t indented
+				}
+				check.errorf(obj.Pos(), "\t%s", obj.Name())
+				// maintain x.mode == typexpr despite error
+				typ = Typ[Invalid]
+				break
+			}
+		}
+
+	case *Var:
+		// It's ok to mark non-local variables, but ignore variables
+		// from other packages to avoid potential race conditions with
+		// dot-imported variables.
+		if obj.pkg == check.pkg {
+			obj.used = true
+		}
+		check.addDeclDep(obj)
+		if typ == Typ[Invalid] {
+			return
+		}
+		x.mode = variable
+
+	case *Func:
+		check.addDeclDep(obj)
+		x.mode = value
+
+	case *Builtin:
+		x.id = obj.id
+		x.mode = builtin
+
+	case *Nil:
+		x.mode = value
+
+	default:
+		unreachable()
+	}
+
+	x.typ = typ
+}
+
+// typExpr type-checks the type expression e and returns its type, or Typ[Invalid].
+// If def != nil, e is the type specification for the named type def, declared
+// in a type declaration, and def.underlying will be set to the type of e before
+// any components of e are type-checked. Path contains the path of named types
+// referring to this type.
+//
+func (check *Checker) typExpr(e ast.Expr, def *Named, path []*TypeName) (T Type) {
+	if trace {
+		check.trace(e.Pos(), "%s", e)
+		check.indent++
+		defer func() {
+			check.indent--
+			check.trace(e.Pos(), "=> %s", T)
+		}()
+	}
+
+	T = check.typExprInternal(e, def, path)
+	assert(isTyped(T))
+	check.recordTypeAndValue(e, typexpr, T, nil)
+
+	return
+}
+
+func (check *Checker) typ(e ast.Expr) Type {
+	return check.typExpr(e, nil, nil)
+}
+
+// funcType type-checks a function or method type.
+func (check *Checker) funcType(sig *Signature, recvPar *ast.FieldList, ftyp *ast.FuncType) {
+	scope := NewScope(check.scope, token.NoPos, token.NoPos, "function")
+	scope.isFunc = true
+	check.recordScope(ftyp, scope)
+
+	recvList, _ := check.collectParams(scope, recvPar, false)
+	params, variadic := check.collectParams(scope, ftyp.Params, true)
+	results, _ := check.collectParams(scope, ftyp.Results, false)
+
+	if recvPar != nil {
+		// recv parameter list present (may be empty)
+		// spec: "The receiver is specified via an extra parameter section preceding the
+		// method name. That parameter section must declare a single parameter, the receiver."
+		var recv *Var
+		switch len(recvList) {
+		case 0:
+			check.error(recvPar.Pos(), "method is missing receiver")
+			recv = NewParam(0, nil, "", Typ[Invalid]) // ignore recv below
+		default:
+			// more than one receiver
+			check.error(recvList[len(recvList)-1].Pos(), "method must have exactly one receiver")
+			fallthrough // continue with first receiver
+		case 1:
+			recv = recvList[0]
+		}
+		// spec: "The receiver type must be of the form T or *T where T is a type name."
+		// (ignore invalid types - error was reported before)
+		if t, _ := deref(recv.typ); t != Typ[Invalid] {
+			var err string
+			if T, _ := t.(*Named); T != nil {
+				// spec: "The type denoted by T is called the receiver base type; it must not
+				// be a pointer or interface type and it must be declared in the same package
+				// as the method."
+				if T.obj.pkg != check.pkg {
+					err = "type not defined in this package"
+				} else {
+					// TODO(gri) This is not correct if the underlying type is unknown yet.
+					switch u := T.underlying.(type) {
+					case *Basic:
+						// unsafe.Pointer is treated like a regular pointer
+						if u.kind == UnsafePointer {
+							err = "unsafe.Pointer"
+						}
+					case *Pointer, *Interface:
+						err = "pointer or interface type"
+					}
+				}
+			} else {
+				err = "basic or unnamed type"
+			}
+			if err != "" {
+				check.errorf(recv.pos, "invalid receiver %s (%s)", recv.typ, err)
+				// ok to continue
+			}
+		}
+		sig.recv = recv
+	}
+
+	sig.scope = scope
+	sig.params = NewTuple(params...)
+	sig.results = NewTuple(results...)
+	sig.variadic = variadic
+}
+
+// typExprInternal drives type checking of types.
+// Must only be called by typExpr.
+//
+func (check *Checker) typExprInternal(e ast.Expr, def *Named, path []*TypeName) Type {
+	switch e := e.(type) {
+	case *ast.BadExpr:
+		// ignore - error reported before
+
+	case *ast.Ident:
+		var x operand
+		check.ident(&x, e, def, path)
+
+		switch x.mode {
+		case typexpr:
+			typ := x.typ
+			def.setUnderlying(typ)
+			return typ
+		case invalid:
+			// ignore - error reported before
+		case novalue:
+			check.errorf(x.pos(), "%s used as type", &x)
+		default:
+			check.errorf(x.pos(), "%s is not a type", &x)
+		}
+
+	case *ast.SelectorExpr:
+		var x operand
+		check.selector(&x, e)
+
+		switch x.mode {
+		case typexpr:
+			typ := x.typ
+			def.setUnderlying(typ)
+			return typ
+		case invalid:
+			// ignore - error reported before
+		case novalue:
+			check.errorf(x.pos(), "%s used as type", &x)
+		default:
+			check.errorf(x.pos(), "%s is not a type", &x)
+		}
+
+	case *ast.ParenExpr:
+		return check.typExpr(e.X, def, path)
+
+	case *ast.ArrayType:
+		if e.Len != nil {
+			typ := new(Array)
+			def.setUnderlying(typ)
+			typ.len = check.arrayLength(e.Len)
+			typ.elem = check.typExpr(e.Elt, nil, path)
+			return typ
+
+		} else {
+			typ := new(Slice)
+			def.setUnderlying(typ)
+			typ.elem = check.typ(e.Elt)
+			return typ
+		}
+
+	case *ast.StructType:
+		typ := new(Struct)
+		def.setUnderlying(typ)
+		check.structType(typ, e, path)
+		return typ
+
+	case *ast.StarExpr:
+		typ := new(Pointer)
+		def.setUnderlying(typ)
+		typ.base = check.typ(e.X)
+		return typ
+
+	case *ast.FuncType:
+		typ := new(Signature)
+		def.setUnderlying(typ)
+		check.funcType(typ, nil, e)
+		return typ
+
+	case *ast.InterfaceType:
+		typ := new(Interface)
+		def.setUnderlying(typ)
+		check.interfaceType(typ, e, def, path)
+		return typ
+
+	case *ast.MapType:
+		typ := new(Map)
+		def.setUnderlying(typ)
+
+		typ.key = check.typ(e.Key)
+		typ.elem = check.typ(e.Value)
+
+		// spec: "The comparison operators == and != must be fully defined
+		// for operands of the key type; thus the key type must not be a
+		// function, map, or slice."
+		//
+		// Delay this check because it requires fully setup types;
+		// it is safe to continue in any case (was issue 6667).
+		check.delay(func() {
+			if !Comparable(typ.key) {
+				check.errorf(e.Key.Pos(), "invalid map key type %s", typ.key)
+			}
+		})
+
+		return typ
+
+	case *ast.ChanType:
+		typ := new(Chan)
+		def.setUnderlying(typ)
+
+		dir := SendRecv
+		switch e.Dir {
+		case ast.SEND | ast.RECV:
+			// nothing to do
+		case ast.SEND:
+			dir = SendOnly
+		case ast.RECV:
+			dir = RecvOnly
+		default:
+			check.invalidAST(e.Pos(), "unknown channel direction %d", e.Dir)
+			// ok to continue
+		}
+
+		typ.dir = dir
+		typ.elem = check.typ(e.Value)
+		return typ
+
+	default:
+		check.errorf(e.Pos(), "%s is not a type", e)
+	}
+
+	typ := Typ[Invalid]
+	def.setUnderlying(typ)
+	return typ
+}
+
+// typeOrNil type-checks the type expression (or nil value) e
+// and returns the typ of e, or nil.
+// If e is neither a type nor nil, typOrNil returns Typ[Invalid].
+//
+func (check *Checker) typOrNil(e ast.Expr) Type {
+	var x operand
+	check.rawExpr(&x, e, nil)
+	switch x.mode {
+	case invalid:
+		// ignore - error reported before
+	case novalue:
+		check.errorf(x.pos(), "%s used as type", &x)
+	case typexpr:
+		return x.typ
+	case value:
+		if x.isNil() {
+			return nil
+		}
+		fallthrough
+	default:
+		check.errorf(x.pos(), "%s is not a type", &x)
+	}
+	return Typ[Invalid]
+}
+
+// arrayLength type-checks the array length expression e
+// and returns the constant length >= 0, or a value < 0
+// to indicate an error (and thus an unknown length).
+func (check *Checker) arrayLength(e ast.Expr) int64 {
+	var x operand
+	check.expr(&x, e)
+	if x.mode != constant_ {
+		if x.mode != invalid {
+			check.errorf(x.pos(), "array length %s must be constant", &x)
+		}
+		return -1
+	}
+	if isUntyped(x.typ) || isInteger(x.typ) {
+		if val := constant.ToInt(x.val); val.Kind() == constant.Int {
+			if representableConst(val, check.conf, Typ[Int], nil) {
+				if n, ok := constant.Int64Val(val); ok && n >= 0 {
+					return n
+				}
+				check.errorf(x.pos(), "invalid array length %s", &x)
+				return -1
+			}
+		}
+	}
+	check.errorf(x.pos(), "array length %s must be integer", &x)
+	return -1
+}
+
+func (check *Checker) collectParams(scope *Scope, list *ast.FieldList, variadicOk bool) (params []*Var, variadic bool) {
+	if list == nil {
+		return
+	}
+
+	var named, anonymous bool
+	for i, field := range list.List {
+		ftype := field.Type
+		if t, _ := ftype.(*ast.Ellipsis); t != nil {
+			ftype = t.Elt
+			if variadicOk && i == len(list.List)-1 {
+				variadic = true
+			} else {
+				check.invalidAST(field.Pos(), "... not permitted")
+				// ignore ... and continue
+			}
+		}
+		typ := check.typ(ftype)
+		// The parser ensures that f.Tag is nil and we don't
+		// care if a constructed AST contains a non-nil tag.
+		if len(field.Names) > 0 {
+			// named parameter
+			for _, name := range field.Names {
+				if name.Name == "" {
+					check.invalidAST(name.Pos(), "anonymous parameter")
+					// ok to continue
+				}
+				par := NewParam(name.Pos(), check.pkg, name.Name, typ)
+				check.declare(scope, name, par, scope.pos)
+				params = append(params, par)
+			}
+			named = true
+		} else {
+			// anonymous parameter
+			par := NewParam(ftype.Pos(), check.pkg, "", typ)
+			check.recordImplicit(field, par)
+			params = append(params, par)
+			anonymous = true
+		}
+	}
+
+	if named && anonymous {
+		check.invalidAST(list.Pos(), "list contains both named and anonymous parameters")
+		// ok to continue
+	}
+
+	// For a variadic function, change the last parameter's type from T to []T.
+	if variadic && len(params) > 0 {
+		last := params[len(params)-1]
+		last.typ = &Slice{elem: last.typ}
+	}
+
+	return
+}
+
+func (check *Checker) declareInSet(oset *objset, pos token.Pos, obj Object) bool {
+	if alt := oset.insert(obj); alt != nil {
+		check.errorf(pos, "%s redeclared", obj.Name())
+		check.reportAltDecl(alt)
+		return false
+	}
+	return true
+}
+
+func (check *Checker) interfaceType(iface *Interface, ityp *ast.InterfaceType, def *Named, path []*TypeName) {
+	// empty interface: common case
+	if ityp.Methods == nil {
+		return
+	}
+
+	// The parser ensures that field tags are nil and we don't
+	// care if a constructed AST contains non-nil tags.
+
+	// use named receiver type if available (for better error messages)
+	var recvTyp Type = iface
+	if def != nil {
+		recvTyp = def
+	}
+
+	// Phase 1: Collect explicitly declared methods, the corresponding
+	//          signature (AST) expressions, and the list of embedded
+	//          type (AST) expressions. Do not resolve signatures or
+	//          embedded types yet to avoid cycles referring to this
+	//          interface.
+
+	var (
+		mset       objset
+		signatures []ast.Expr // list of corresponding method signatures
+		embedded   []ast.Expr // list of embedded types
+	)
+	for _, f := range ityp.Methods.List {
+		if len(f.Names) > 0 {
+			// The parser ensures that there's only one method
+			// and we don't care if a constructed AST has more.
+			name := f.Names[0]
+			pos := name.Pos()
+			// spec: "As with all method sets, in an interface type,
+			// each method must have a unique non-blank name."
+			if name.Name == "_" {
+				check.errorf(pos, "invalid method name _")
+				continue
+			}
+			// Don't type-check signature yet - use an
+			// empty signature now and update it later.
+			// Since we know the receiver, set it up now
+			// (required to avoid crash in ptrRecv; see
+			// e.g. test case for issue 6638).
+			// TODO(gri) Consider marking methods signatures
+			// as incomplete, for better error messages. See
+			// also the T4 and T5 tests in testdata/cycles2.src.
+			sig := new(Signature)
+			sig.recv = NewVar(pos, check.pkg, "", recvTyp)
+			m := NewFunc(pos, check.pkg, name.Name, sig)
+			if check.declareInSet(&mset, pos, m) {
+				iface.methods = append(iface.methods, m)
+				iface.allMethods = append(iface.allMethods, m)
+				signatures = append(signatures, f.Type)
+				check.recordDef(name, m)
+			}
+		} else {
+			// embedded type
+			embedded = append(embedded, f.Type)
+		}
+	}
+
+	// Phase 2: Resolve embedded interfaces. Because an interface must not
+	//          embed itself (directly or indirectly), each embedded interface
+	//          can be fully resolved without depending on any method of this
+	//          interface (if there is a cycle or another error, the embedded
+	//          type resolves to an invalid type and is ignored).
+	//          In particular, the list of methods for each embedded interface
+	//          must be complete (it cannot depend on this interface), and so
+	//          those methods can be added to the list of all methods of this
+	//          interface.
+
+	for _, e := range embedded {
+		pos := e.Pos()
+		typ := check.typExpr(e, nil, path)
+		// Determine underlying embedded (possibly incomplete) type
+		// by following its forward chain.
+		named, _ := typ.(*Named)
+		under := underlying(named)
+		embed, _ := under.(*Interface)
+		if embed == nil {
+			if typ != Typ[Invalid] {
+				check.errorf(pos, "%s is not an interface", typ)
+			}
+			continue
+		}
+		iface.embeddeds = append(iface.embeddeds, named)
+		// collect embedded methods
+		if embed.allMethods == nil {
+			check.errorf(pos, "internal error: incomplete embedded interface %s (issue #18395)", named)
+		}
+		for _, m := range embed.allMethods {
+			if check.declareInSet(&mset, pos, m) {
+				iface.allMethods = append(iface.allMethods, m)
+			}
+		}
+	}
+
+	// Phase 3: At this point all methods have been collected for this interface.
+	//          It is now safe to type-check the signatures of all explicitly
+	//          declared methods, even if they refer to this interface via a cycle
+	//          and embed the methods of this interface in a parameter of interface
+	//          type.
+
+	for i, m := range iface.methods {
+		expr := signatures[i]
+		typ := check.typ(expr)
+		sig, _ := typ.(*Signature)
+		if sig == nil {
+			if typ != Typ[Invalid] {
+				check.invalidAST(expr.Pos(), "%s is not a method signature", typ)
+			}
+			continue // keep method with empty method signature
+		}
+		// update signature, but keep recv that was set up before
+		old := m.typ.(*Signature)
+		sig.recv = old.recv
+		*old = *sig // update signature (don't replace it!)
+	}
+
+	// TODO(gri) The list of explicit methods is only sorted for now to
+	// produce the same Interface as NewInterface. We may be able to
+	// claim source order in the future. Revisit.
+	sort.Sort(byUniqueMethodName(iface.methods))
+
+	// TODO(gri) The list of embedded types is only sorted for now to
+	// produce the same Interface as NewInterface. We may be able to
+	// claim source order in the future. Revisit.
+	sort.Sort(byUniqueTypeName(iface.embeddeds))
+
+	if iface.allMethods == nil {
+		iface.allMethods = make([]*Func, 0) // mark interface as complete
+	} else {
+		sort.Sort(byUniqueMethodName(iface.allMethods))
+	}
+}
+
+// byUniqueTypeName named type lists can be sorted by their unique type names.
+type byUniqueTypeName []*Named
+
+func (a byUniqueTypeName) Len() int           { return len(a) }
+func (a byUniqueTypeName) Less(i, j int) bool { return a[i].obj.Id() < a[j].obj.Id() }
+func (a byUniqueTypeName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
+// byUniqueMethodName method lists can be sorted by their unique method names.
+type byUniqueMethodName []*Func
+
+func (a byUniqueMethodName) Len() int           { return len(a) }
+func (a byUniqueMethodName) Less(i, j int) bool { return a[i].Id() < a[j].Id() }
+func (a byUniqueMethodName) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
+
+func (check *Checker) tag(t *ast.BasicLit) string {
+	if t != nil {
+		if t.Kind == token.STRING {
+			if val, err := strconv.Unquote(t.Value); err == nil {
+				return val
+			}
+		}
+		check.invalidAST(t.Pos(), "incorrect tag syntax: %q", t.Value)
+	}
+	return ""
+}
+
+func (check *Checker) structType(styp *Struct, e *ast.StructType, path []*TypeName) {
+	list := e.Fields
+	if list == nil {
+		return
+	}
+
+	// struct fields and tags
+	var fields []*Var
+	var tags []string
+
+	// for double-declaration checks
+	var fset objset
+
+	// current field typ and tag
+	var typ Type
+	var tag string
+	add := func(ident *ast.Ident, anonymous bool, pos token.Pos) {
+		if tag != "" && tags == nil {
+			tags = make([]string, len(fields))
+		}
+		if tags != nil {
+			tags = append(tags, tag)
+		}
+
+		name := ident.Name
+		fld := NewField(pos, check.pkg, name, typ, anonymous)
+		// spec: "Within a struct, non-blank field names must be unique."
+		if name == "_" || check.declareInSet(&fset, pos, fld) {
+			fields = append(fields, fld)
+			check.recordDef(ident, fld)
+		}
+	}
+
+	for _, f := range list.List {
+		typ = check.typExpr(f.Type, nil, path)
+		tag = check.tag(f.Tag)
+		if len(f.Names) > 0 {
+			// named fields
+			for _, name := range f.Names {
+				add(name, false, name.Pos())
+			}
+		} else {
+			// anonymous field
+			// spec: "An embedded type must be specified as a type name T or as a pointer
+			// to a non-interface type name *T, and T itself may not be a pointer type."
+			pos := f.Type.Pos()
+			name := anonymousFieldIdent(f.Type)
+			if name == nil {
+				check.invalidAST(pos, "anonymous field type %s has no name", f.Type)
+				continue
+			}
+			t, isPtr := deref(typ)
+			// Because we have a name, typ must be of the form T or *T, where T is the name
+			// of a (named or alias) type, and t (= deref(typ)) must be the type of T.
+			switch t := t.Underlying().(type) {
+			case *Basic:
+				if t == Typ[Invalid] {
+					// error was reported before
+					continue
+				}
+
+				// unsafe.Pointer is treated like a regular pointer
+				if t.kind == UnsafePointer {
+					check.errorf(pos, "anonymous field type cannot be unsafe.Pointer")
+					continue
+				}
+
+			case *Pointer:
+				check.errorf(pos, "anonymous field type cannot be a pointer")
+				continue
+
+			case *Interface:
+				if isPtr {
+					check.errorf(pos, "anonymous field type cannot be a pointer to an interface")
+					continue
+				}
+			}
+			add(name, true, pos)
+		}
+	}
+
+	styp.fields = fields
+	styp.tags = tags
+}
+
+func anonymousFieldIdent(e ast.Expr) *ast.Ident {
+	switch e := e.(type) {
+	case *ast.Ident:
+		return e
+	case *ast.StarExpr:
+		// *T is valid, but **T is not
+		if _, ok := e.X.(*ast.StarExpr); !ok {
+			return anonymousFieldIdent(e.X)
+		}
+	case *ast.SelectorExpr:
+		return e.Sel
+	}
+	return nil // invalid anonymous field
+}

third_party/forked/golang/go/types/universe.go

+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file sets up the universe scope and the unsafe package.
+
+package types
+
+import (
+	"go/constant"
+	"go/token"
+	"strings"
+)
+
+var (
+	Universe     *Scope
+	Unsafe       *Package
+	universeIota *Const
+	universeByte *Basic // uint8 alias, but has name "byte"
+	universeRune *Basic // int32 alias, but has name "rune"
+)
+
+// Typ contains the predeclared *Basic types indexed by their
+// corresponding BasicKind.
+//
+// The *Basic type for Typ[Byte] will have the name "uint8".
+// Use Universe.Lookup("byte").Type() to obtain the specific
+// alias basic type named "byte" (and analogous for "rune").
+var Typ = []*Basic{
+	Invalid: {Invalid, 0, "invalid type"},
+
+	Bool:          {Bool, IsBoolean, "bool"},
+	Int:           {Int, IsInteger, "int"},
+	Int8:          {Int8, IsInteger, "int8"},
+	Int16:         {Int16, IsInteger, "int16"},
+	Int32:         {Int32, IsInteger, "int32"},
+	Int64:         {Int64, IsInteger, "int64"},
+	Uint:          {Uint, IsInteger | IsUnsigned, "uint"},
+	Uint8:         {Uint8, IsInteger | IsUnsigned, "uint8"},
+	Uint16:        {Uint16, IsInteger | IsUnsigned, "uint16"},
+	Uint32:        {Uint32, IsInteger | IsUnsigned, "uint32"},
+	Uint64:        {Uint64, IsInteger | IsUnsigned, "uint64"},
+	Uintptr:       {Uintptr, IsInteger | IsUnsigned, "uintptr"},
+	Float32:       {Float32, IsFloat, "float32"},
+	Float64:       {Float64, IsFloat, "float64"},
+	Complex64:     {Complex64, IsComplex, "complex64"},
+	Complex128:    {Complex128, IsComplex, "complex128"},
+	String:        {String, IsString, "string"},
+	UnsafePointer: {UnsafePointer, 0, "Pointer"},
+
+	UntypedBool:    {UntypedBool, IsBoolean | IsUntyped, "untyped bool"},
+	UntypedInt:     {UntypedInt, IsInteger | IsUntyped, "untyped int"},
+	UntypedRune:    {UntypedRune, IsInteger | IsUntyped, "untyped rune"},
+	UntypedFloat:   {UntypedFloat, IsFloat | IsUntyped, "untyped float"},
+	UntypedComplex: {UntypedComplex, IsComplex | IsUntyped, "untyped complex"},
+	UntypedString:  {UntypedString, IsString | IsUntyped, "untyped string"},
+	UntypedNil:     {UntypedNil, IsUntyped, "untyped nil"},
+}
+
+var aliases = [...]*Basic{
+	{Byte, IsInteger | IsUnsigned, "byte"},
+	{Rune, IsInteger, "rune"},
+}
+
+func defPredeclaredTypes() {
+	for _, t := range Typ {
+		def(NewTypeName(token.NoPos, nil, t.name, t))
+	}
+	for _, t := range aliases {
+		def(NewTypeName(token.NoPos, nil, t.name, t))
+	}
+
+	// Error has a nil package in its qualified name since it is in no package
+	res := NewVar(token.NoPos, nil, "", Typ[String])
+	sig := &Signature{results: NewTuple(res)}
+	err := NewFunc(token.NoPos, nil, "Error", sig)
+	typ := &Named{underlying: NewInterface([]*Func{err}, nil).Complete()}
+	sig.recv = NewVar(token.NoPos, nil, "", typ)
+	def(NewTypeName(token.NoPos, nil, "error", typ))
+}
+
+var predeclaredConsts = [...]struct {
+	name string
+	kind BasicKind
+	val  constant.Value
+}{
+	{"true", UntypedBool, constant.MakeBool(true)},
+	{"false", UntypedBool, constant.MakeBool(false)},
+	{"iota", UntypedInt, constant.MakeInt64(0)},
+}
+
+func defPredeclaredConsts() {
+	for _, c := range predeclaredConsts {
+		def(NewConst(token.NoPos, nil, c.name, Typ[c.kind], c.val))
+	}
+}
+
+func defPredeclaredNil() {
+	def(&Nil{object{name: "nil", typ: Typ[UntypedNil]}})
+}
+
+// A builtinId is the id of a builtin function.
+type builtinId int
+
+const (
+	// universe scope
+	_Append builtinId = iota
+	_Cap
+	_Close
+	_Complex
+	_Copy
+	_Delete
+	_Imag
+	_Len
+	_Make
+	_New
+	_Panic
+	_Print
+	_Println
+	_Real
+	_Recover
+
+	// package unsafe
+	_Alignof
+	_Offsetof
+	_Sizeof
+
+	// testing support
+	_Assert
+	_Trace
+)
+
+var predeclaredFuncs = [...]struct {
+	name     string
+	nargs    int
+	variadic bool
+	kind     exprKind
+}{
+	_Append:  {"append", 1, true, expression},
+	_Cap:     {"cap", 1, false, expression},
+	_Close:   {"close", 1, false, statement},
+	_Complex: {"complex", 2, false, expression},
+	_Copy:    {"copy", 2, false, statement},
+	_Delete:  {"delete", 2, false, statement},
+	_Imag:    {"imag", 1, false, expression},
+	_Len:     {"len", 1, false, expression},
+	_Make:    {"make", 1, true, expression},
+	_New:     {"new", 1, false, expression},
+	_Panic:   {"panic", 1, false, statement},
+	_Print:   {"print", 0, true, statement},
+	_Println: {"println", 0, true, statement},
+	_Real:    {"real", 1, false, expression},
+	_Recover: {"recover", 0, false, statement},
+
+	_Alignof:  {"Alignof", 1, false, expression},
+	_Offsetof: {"Offsetof", 1, false, expression},
+	_Sizeof:   {"Sizeof", 1, false, expression},
+
+	_Assert: {"assert", 1, false, statement},
+	_Trace:  {"trace", 0, true, statement},
+}
+
+func defPredeclaredFuncs() {
+	for i := range predeclaredFuncs {
+		id := builtinId(i)
+		if id == _Assert || id == _Trace {
+			continue // only define these in testing environment
+		}
+		def(newBuiltin(id))
+	}
+}
+
+// DefPredeclaredTestFuncs defines the assert and trace built-ins.
+// These built-ins are intended for debugging and testing of this
+// package only.
+func DefPredeclaredTestFuncs() {
+	if Universe.Lookup("assert") != nil {
+		return // already defined
+	}
+	def(newBuiltin(_Assert))
+	def(newBuiltin(_Trace))
+}
+
+func init() {
+	Universe = NewScope(nil, token.NoPos, token.NoPos, "universe")
+	Unsafe = NewPackage("unsafe", "unsafe")
+	Unsafe.complete = true
+
+	defPredeclaredTypes()
+	defPredeclaredConsts()
+	defPredeclaredNil()
+	defPredeclaredFuncs()
+
+	universeIota = Universe.Lookup("iota").(*Const)
+	universeByte = Universe.Lookup("byte").(*TypeName).typ.(*Basic)
+	universeRune = Universe.Lookup("rune").(*TypeName).typ.(*Basic)
+}
+
+// Objects with names containing blanks are internal and not entered into
+// a scope. Objects with exported names are inserted in the unsafe package
+// scope; other objects are inserted in the universe scope.
+//
+func def(obj Object) {
+	name := obj.Name()
+	if strings.Contains(name, " ") {
+		return // nothing to do
+	}
+	// fix Obj link for named types
+	if typ, ok := obj.Type().(*Named); ok {
+		typ.obj = obj.(*TypeName)
+	}
+	// exported identifiers go into package unsafe
+	scope := Universe
+	if obj.Exported() {
+		scope = Unsafe.scope
+		// set Pkg field
+		switch obj := obj.(type) {
+		case *TypeName:
+			obj.pkg = Unsafe
+		case *Builtin:
+			obj.pkg = Unsafe
+		default:
+			unreachable()
+		}
+	}
+	if scope.Insert(obj) != nil {
+		panic("internal error: double declaration")
+	}
+}