Create a kubectl alpha subcommand

Alpha commands can be added under `kubectl alpha` and are always
accessible (regardless of feature gates). If no alpha commands have been
defined then `alpha` is not displayed in `help`.

docs/.generated_docs

@@ -10,6 +10,7 @@ docs/man/man1/kube-apiserver.1
 docs/man/man1/kube-controller-manager.1
 docs/man/man1/kube-proxy.1
 docs/man/man1/kube-scheduler.1
+docs/man/man1/kubectl-alpha.1
 docs/man/man1/kubectl-annotate.1
 docs/man/man1/kubectl-api-versions.1
 docs/man/man1/kubectl-apply-set-last-applied.1
@@ -189,6 +190,7 @@ docs/user-guide/kubectl/kubectl_top_pod.md
 docs/user-guide/kubectl/kubectl_uncordon.md
 docs/user-guide/kubectl/kubectl_version.md
 docs/yaml/kubectl/kubectl.yaml
+docs/yaml/kubectl/kubectl_alpha.yaml
 docs/yaml/kubectl/kubectl_annotate.yaml
 docs/yaml/kubectl/kubectl_api-versions.yaml
 docs/yaml/kubectl/kubectl_apply.yaml

docs/man/man1/kubectl-alpha.1

@@ -0,0 +1,3 @@
+This file is autogenerated, but we've stopped checking such files into the
+repository to reduce the need for rebases. Please run hack/generate-docs.sh to
+populate this file.

docs/yaml/kubectl/kubectl_alpha.yaml

@@ -0,0 +1,3 @@
+This file is autogenerated, but we've stopped checking such files into the
+repository to reduce the need for rebases. Please run hack/generate-docs.sh to
+populate this file.

pkg/kubectl/cmd/BUILD

@@ -9,6 +9,7 @@ load(
 go_library(
     name = "go_default_library",
     srcs = [
+        "alpha.go",
         "annotate.go",
         "apiversions.go",
         "apply.go",

pkg/kubectl/cmd/alpha.go

@@ -0,0 +1,50 @@
+/*
+Copyright 2017 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package cmd
+
+import (
+	"io"
+
+	"github.com/spf13/cobra"
+
+	"k8s.io/kubernetes/pkg/kubectl/cmd/templates"
+	cmdutil "k8s.io/kubernetes/pkg/kubectl/cmd/util"
+	"k8s.io/kubernetes/pkg/util/i18n"
+)
+
+// NewCmdAlpha creates a command that acts as an alternate root command for features in alpha
+func NewCmdAlpha(f cmdutil.Factory, in io.Reader, out, err io.Writer) *cobra.Command {
+	cmd := &cobra.Command{
+		Use:   "alpha",
+		Short: i18n.T("Commands for features in alpha"),
+		Long:  templates.LongDesc(i18n.T("These commands correspond to alpha features that are not enabled in Kubernetes clusters by default.")),
+	}
+
+	// Alpha commands should be added here. As features graduate from alpha they should move
+	// from here to the CommandGroups defined by NewKubeletCommand() in cmd.go.
+	//cmd.AddCommand(NewCmdDebug(f, in, out, err))
+
+	// NewKubeletCommand() will hide the alpha command if it has no subcommands. Overriding
+	// the help function ensures a reasonable message if someone types the hidden command anyway.
+	if !cmd.HasSubCommands() {
+		cmd.SetHelpFunc(func(*cobra.Command, []string) {
+			cmd.Println(i18n.T("No alpha commands are available in this version of kubectl"))
+		})
+	}
+
+	return cmd
+}

pkg/kubectl/cmd/cmd.go

@@ -354,6 +354,13 @@ func NewKubectlCommand(f cmdutil.Factory, in io.Reader, out, err io.Writer) *cob
 		"options",
 		Deprecated("kubectl", "delete", cmds, NewCmdStop(f, out)),
 	}
+
+	// Hide the "alpha" subcommand if there are no alpha commands in this build.
+	alpha := NewCmdAlpha(f, in, out, err)
+	if !alpha.HasSubCommands() {
+		filters = append(filters, alpha.Name())
+	}
+
 	templates.ActsAsRootCommand(cmds, filters, groups...)
 
 	for name, completion := range bash_completion_flags {
@@ -368,6 +375,7 @@ func NewKubectlCommand(f cmdutil.Factory, in io.Reader, out, err io.Writer) *cob
 		}
 	}
 
+	cmds.AddCommand(alpha)
 	cmds.AddCommand(cmdconfig.NewCmdConfig(clientcmd.NewDefaultPathOptions(), out, err))
 	cmds.AddCommand(NewCmdPlugin(f, in, out, err))
 	cmds.AddCommand(NewCmdVersion(f, out))