fix kubectl set selector

pkg/kubectl/cmd/set/BUILD

@@ -30,6 +30,7 @@ go_library(
         "//pkg/runtime:go_default_library",
         "//pkg/util/errors:go_default_library",
         "//pkg/util/strategicpatch:go_default_library",
+        "//pkg/util/validation:go_default_library",
         "//vendor:github.com/spf13/cobra",
     ],
 )

pkg/kubectl/cmd/set/set_selector.go

@@ -29,6 +29,7 @@ import (
 	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
 	"k8s.io/kubernetes/pkg/kubectl/resource"
 	"k8s.io/kubernetes/pkg/runtime"
+	"k8s.io/kubernetes/pkg/util/validation"
 )
 
 // SelectorOptions is the start of the data required to perform the operation.  As new fields are added, add them here instead of
@@ -77,7 +78,7 @@ func NewCmdSelector(f cmdutil.Factory, out io.Writer) *cobra.Command {
 	cmd := &cobra.Command{
 		Use:     "selector (-f FILENAME | TYPE NAME) EXPRESSIONS [--resource-version=version]",
 		Short:   "Set the selector on a resource",
-		Long:    fmt.Sprintf(selectorLong),
+		Long:    fmt.Sprintf(selectorLong, validation.LabelValueMaxLength),
 		Example: selectorExample,
 		Run: func(cmd *cobra.Command, args []string) {
 			cmdutil.CheckErr(options.Complete(f, cmd, args, out))
@@ -136,6 +137,9 @@ func (o *SelectorOptions) Validate() error {
 	if len(o.resources) < 1 && cmdutil.IsFilenameEmpty(o.fileOptions.Filenames) {
 		return fmt.Errorf("one or more resources must be specified as <resource> <name> or <resource>/<name>")
 	}
+	if o.selector == nil {
+		return fmt.Errorf("one selector is required")
+	}
 	return nil
 }
 
@@ -213,9 +217,10 @@ func updateSelectorForObject(obj runtime.Object, selector metav1.LabelSelector)
 
 // getResourcesAndSelector retrieves resources and the selector expression from the given args (assuming selectors the last arg)
 func getResourcesAndSelector(args []string) (resources []string, selector *metav1.LabelSelector, err error) {
-	if len(args) > 1 {
-		resources = args[:len(args)-1]
+	if len(args) == 0 {
+		return []string{}, nil, nil
 	}
+	resources = args[:len(args)-1]
 	selector, err = metav1.ParseToLabelSelector(args[len(args)-1])
 	return resources, selector, err
 }

pkg/kubectl/cmd/set/set_selector_test.go

@@ -283,6 +283,13 @@ func TestGetResourcesAndSelector(t *testing.T) {
 				MatchExpressions: []metav1.LabelSelectorRequirement{},
 			},
 		},
+		{
+			name:          "no resource and selector",
+			args:          args{args: []string{}},
+			wantResources: []string{},
+			wantErr:       false,
+			wantSelector:  nil,
+		},
 	}
 	for _, tt := range tests {
 		gotResources, gotSelector, err := getResourcesAndSelector(tt.args.args)