Adds support to a tree hierarchy of kubectl plugins

pkg/kubectl/plugins/plugins.go

@@ -16,7 +16,10 @@ limitations under the License.
 
 package plugins
 
-import "fmt"
+import (
+	"fmt"
+	"strings"
+)
 
 // Plugin is the representation of a CLI extension (plugin).
 type Plugin struct {
@@ -28,11 +31,12 @@ type Plugin struct {
 // PluginDescription holds everything needed to register a
 // plugin as a command. Usually comes from a descriptor file.
 type Description struct {
-	Name      string `json:"name"`
-	ShortDesc string `json:"shortDesc"`
-	LongDesc  string `json:"longDesc,omitempty"`
-	Example   string `json:"example,omitempty"`
-	Command   string `json:"command"`
+	Name      string    `json:"name"`
+	ShortDesc string    `json:"shortDesc"`
+	LongDesc  string    `json:"longDesc,omitempty"`
+	Example   string    `json:"example,omitempty"`
+	Command   string    `json:"command"`
+	Tree      []*Plugin `json:"tree,omitempty"`
 }
 
 // PluginSource holds the location of a given plugin in the filesystem.
@@ -41,12 +45,23 @@ type Source struct {
 	DescriptorName string `json:"-"`
 }
 
-var IncompleteError = fmt.Errorf("incomplete plugin descriptor: name, shortDesc and command fields are required")
+var (
+	IncompleteError  = fmt.Errorf("incomplete plugin descriptor: name, shortDesc and command fields are required")
+	InvalidNameError = fmt.Errorf("plugin name can't contain spaces")
+)
 
 func (p Plugin) Validate() error {
-	if len(p.Name) == 0 || len(p.ShortDesc) == 0 || len(p.Command) == 0 {
+	if len(p.Name) == 0 || len(p.ShortDesc) == 0 || (len(p.Command) == 0 && len(p.Tree) == 0) {
 		return IncompleteError
 	}
+	if strings.Index(p.Name, " ") > -1 {
+		return InvalidNameError
+	}
+	for _, child := range p.Tree {
+		if err := child.Validate(); err != nil {
+			return err
+		}
+	}
 	return nil
 }