Integrate CLI plugins with `docker «plugin» --help`.

To achieve this we hook in at the beginning of our custom `HelpFunc` and detect
the plugin case by adding stub commands.

Signed-off-by: Ian Campbell <ijc@docker.com>

cmd/docker/docker.go

@@ -123,6 +123,21 @@ func setupHelpCommand(dockerCli *command.DockerCli, rootCmd, helpCmd *cobra.Comm
 	}
 }
 
+func tryRunPluginHelp(dockerCli command.Cli, ccmd *cobra.Command, cargs []string) error {
+	root := ccmd.Root()
+	pluginmanager.AddPluginCommandStubs(dockerCli, root, false)
+
+	cmd, _, err := root.Traverse(cargs)
+	if err != nil {
+		return err
+	}
+	helpcmd, err := pluginmanager.PluginRunCommand(dockerCli, cmd.Name(), root)
+	if err != nil {
+		return err
+	}
+	return helpcmd.Run()
+}
+
 func setHelpFunc(dockerCli *command.DockerCli, cmd *cobra.Command, flags *pflag.FlagSet, opts *cliflags.ClientOptions) {
 	defaultHelpFunc := cmd.HelpFunc()
 	cmd.SetHelpFunc(func(ccmd *cobra.Command, args []string) {
@@ -130,6 +145,17 @@ func setHelpFunc(dockerCli *command.DockerCli, cmd *cobra.Command, flags *pflag.
 			ccmd.Println(err)
 			return
 		}
+		if len(args) >= 1 {
+			err := tryRunPluginHelp(dockerCli, ccmd, args)
+			if err == nil { // Successfully ran the plugin
+				return
+			}
+			if !pluginmanager.IsNotFound(err) {
+				ccmd.Println(err)
+				return
+			}
+		}
+
 		if err := isSupported(ccmd, dockerCli); err != nil {
 			ccmd.Println(err)
 			return

e2e/cli-plugins/run_test.go

@@ -35,6 +35,22 @@ func TestHelpNonexisting(t *testing.T) {
 	golden.Assert(t, res.Stderr(), "docker-help-nonexistent-err.golden")
 }
 
+// TestNonexistingHelp ensures correct behaviour when invoking a
+// nonexistent plugin with `--help`.
+func TestNonexistingHelp(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("nonexistent", "--help"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 0,
+		// This should actually be the whole docker help
+		// output, so spot check instead having of a golden
+		// with everything in, which will change too frequently.
+		Out: "Usage:	docker [OPTIONS] COMMAND\n\nA self-sufficient runtime for containers",
+	})
+}
+
 // TestRunBad ensures correct behaviour when running an existent but invalid plugin
 func TestRunBad(t *testing.T) {
 	run, cleanup := prepare(t)
@@ -61,6 +77,22 @@ func TestHelpBad(t *testing.T) {
 	golden.Assert(t, res.Stderr(), "docker-help-badmeta-err.golden")
 }
 
+// TestBadHelp ensures correct behaviour when invoking an
+// existent but invalid plugin with `--help`.
+func TestBadHelp(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("badmeta", "--help"))
+	res.Assert(t, icmd.Expected{
+		ExitCode: 0,
+		// This should be literally the whole docker help
+		// output, so spot check instead of a golden with
+		// everything in which will change all the time.
+		Out: "Usage:	docker [OPTIONS] COMMAND\n\nA self-sufficient runtime for containers",
+	})
+}
+
 // TestRunGood ensures correct behaviour when running a valid plugin
 func TestRunGood(t *testing.T) {
 	run, cleanup := prepare(t)
@@ -86,6 +118,20 @@ func TestHelpGood(t *testing.T) {
 	assert.Assert(t, is.Equal(res.Stderr(), ""))
 }
 
+// TestGoodHelp ensures correct behaviour when calling a valid plugin
+// with `--help`. A global argument is used to ensure it does not
+// interfere.
+func TestGoodHelp(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("-D", "helloworld", "--help"))
+	res.Assert(t, icmd.Success)
+	// This is the same golden file as `TestHelpGood`, above.
+	golden.Assert(t, res.Stdout(), "docker-help-helloworld.golden")
+	assert.Assert(t, is.Equal(res.Stderr(), ""))
+}
+
 // TestRunGoodSubcommand ensures correct behaviour when running a valid plugin with a subcommand
 func TestRunGoodSubcommand(t *testing.T) {
 	run, cleanup := prepare(t)
@@ -110,3 +156,17 @@ func TestHelpGoodSubcommand(t *testing.T) {
 	golden.Assert(t, res.Stdout(), "docker-help-helloworld-goodbye.golden")
 	assert.Assert(t, is.Equal(res.Stderr(), ""))
 }
+
+// TestGoodSubcommandHelp ensures correct behaviour when calling a valid plugin
+// with a subcommand and `--help`. A global argument is used to ensure it does not
+// interfere.
+func TestGoodSubcommandHelp(t *testing.T) {
+	run, cleanup := prepare(t)
+	defer cleanup()
+
+	res := icmd.RunCmd(run("-D", "helloworld", "goodbye", "--help"))
+	res.Assert(t, icmd.Success)
+	// This is the same golden file as `TestHelpGoodSubcommand`, above.
+	golden.Assert(t, res.Stdout(), "docker-help-helloworld-goodbye.golden")
+	assert.Assert(t, is.Equal(res.Stderr(), ""))
+}