load plugin command stubs when required

We are currently loading plugin command stubs for every
invocation which still has a significant performance hit.
With this change we are doing this operation only if cobra
completion arg request is found.

- 20.10.23: `docker --version` takes ~15ms
- 23.0.1: `docker --version` takes ~93ms

With this change `docker --version` takes ~9ms

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>
(cherry picked from commit c39c711a18)

cli-plugins/manager/cobra.go

@@ -3,6 +3,7 @@ package manager
 import (
 	"fmt"
 	"os"
+	"sync"
 
 	"github.com/docker/cli/cli/command"
 	"github.com/spf13/cobra"
@@ -31,13 +32,17 @@ const (
 	CommandAnnotationPluginInvalid = "com.docker.cli.plugin-invalid"
 )
 
+var pluginCommandStubsOnce sync.Once
+
 // AddPluginCommandStubs adds a stub cobra.Commands for each valid and invalid
 // plugin. The command stubs will have several annotations added, see
 // `CommandAnnotationPlugin*`.
-func AddPluginCommandStubs(dockerCli command.Cli, rootCmd *cobra.Command) error {
+func AddPluginCommandStubs(dockerCli command.Cli, rootCmd *cobra.Command) (err error) {
-	plugins, err := ListPlugins(dockerCli, rootCmd)
+	pluginCommandStubsOnce.Do(func() {
+		var plugins []Plugin
+		plugins, err = ListPlugins(dockerCli, rootCmd)
 		if err != nil {
-		return err
+			return
 		}
 		for _, p := range plugins {
 			p := p
@@ -62,8 +67,8 @@ func AddPluginCommandStubs(dockerCli command.Cli, rootCmd *cobra.Command) error
 				RunE: func(cmd *cobra.Command, args []string) error {
 					flags := rootCmd.PersistentFlags()
 					flags.SetOutput(nil)
-				err := flags.Parse(args)
+					perr := flags.Parse(args)
-				if err != nil {
+					if perr != nil {
 						return err
 					}
 					if flags.Changed("help") {
@@ -78,17 +83,18 @@ func AddPluginCommandStubs(dockerCli command.Cli, rootCmd *cobra.Command) error
 					cargs = append(cargs, args...)
 					cargs = append(cargs, toComplete)
 					os.Args = cargs
-				runCommand, err := PluginRunCommand(dockerCli, p.Name, cmd)
+					runCommand, runErr := PluginRunCommand(dockerCli, p.Name, cmd)
-				if err != nil {
+					if runErr != nil {
 						return nil, cobra.ShellCompDirectiveError
 					}
-				err = runCommand.Run()
+					runErr = runCommand.Run()
-				if err == nil {
+					if runErr == nil {
 						os.Exit(0) // plugin already rendered complete data
 					}
 					return nil, cobra.ShellCompDirectiveError
 				},
 			})
 		}
-	return nil
+	})
+	return err
 }

cli/cobra.go

@@ -204,6 +204,16 @@ func DisableFlagsInUseLine(cmd *cobra.Command) {
 	})
 }
 
+// HasCompletionArg returns true if a cobra completion arg request is found.
+func HasCompletionArg(args []string) bool {
+	for _, arg := range args {
+		if arg == cobra.ShellCompRequestCmd || arg == cobra.ShellCompNoDescRequestCmd {
+			return true
+		}
+	}
+	return false
+}
+
 var helpCommand = &cobra.Command{
 	Use:               "help [command]",
 	Short:             "Help about the command",

cmd/docker/docker.go

@@ -133,14 +133,21 @@ func tryRunPluginHelp(dockerCli command.Cli, ccmd *cobra.Command, cargs []string
 func setHelpFunc(dockerCli command.Cli, cmd *cobra.Command) {
 	defaultHelpFunc := cmd.HelpFunc()
 	cmd.SetHelpFunc(func(ccmd *cobra.Command, args []string) {
-		if pluginmanager.IsPluginCommand(ccmd) {
+		if err := pluginmanager.AddPluginCommandStubs(dockerCli, ccmd.Root()); err != nil {
+			ccmd.Println(err)
+			return
+		}
+
+		if len(args) >= 1 {
 			err := tryRunPluginHelp(dockerCli, ccmd, args)
+			if err == nil {
+				return
+			}
 			if !pluginmanager.IsNotFound(err) {
 				ccmd.Println(err)
-			}
-			cmd.PrintErrf("unknown help topic: %v\n", ccmd.Name())
 				return
 			}
+		}
 
 		if err := isSupported(ccmd, dockerCli); err != nil {
 			ccmd.Println(err)
@@ -227,10 +234,15 @@ func runDocker(dockerCli *command.DockerCli) error {
 		return err
 	}
 
+	if cli.HasCompletionArg(args) {
+		// We add plugin command stubs early only for completion. We don't
+		// want to add them for normal command execution as it would cause
+		// a significant performance hit.
 		err = pluginmanager.AddPluginCommandStubs(dockerCli, cmd)
 		if err != nil {
 			return err
 		}
+	}
 
 	if len(args) > 0 {
 		ccmd, _, err := cmd.Find(args)

e2e/cli-plugins/run_test.go

@@ -83,7 +83,7 @@ func TestHelpBad(t *testing.T) {
 
 	res := icmd.RunCmd(run("help", "badmeta"))
 	res.Assert(t, icmd.Expected{
-		ExitCode: 0,
+		ExitCode: 1,
 		Out:      icmd.None,
 	})
 	golden.Assert(t, res.Stderr(), "docker-help-badmeta-err.golden")
@@ -110,8 +110,8 @@ func TestBadHelp(t *testing.T) {
 	res.Assert(t, icmd.Expected{
 		ExitCode: 0,
 		// This should be identical to the --help case above
-		Out: usage,
+		Out: shortHFlagDeprecated + usage,
-		Err: shortHFlagDeprecated,
+		Err: icmd.None,
 	})
 }