Merge pull request #46151 from verb/kubectl-featuregate

Automatic merge from submit-queue

Add alpha command to kubectl

Also allow new commands to disable themselves by returning a nil value. This can be used to disable commands based on feature gates.

**What this PR does / why we need it**: Method of enabling alpha functionality in kubectl

**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: ref #45922

**Special notes for your reviewer**: Part of a discussion in #45922 with @pwittrock

**Release note**:

```release-note
NONE
```

pkg/kubectl/cmd/cmd.go

@@ -360,6 +360,13 @@ 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 {
@@ -374,6 +381,7 @@ 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))