fix: show swarm init help instead of docker-init plugin help

When the docker-init CLI plugin is installed, `docker swarm init --help`
incorrectly delegated to the plugin because help handling matched on the
command name "init" without checking whether the target was a plugin stub.

Fixes #4400

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: hernandanielg

cmd/docker/docker.go

@@ -229,14 +229,11 @@ func setupHelpCommand(dockerCli command.Cli, rootCmd, helpCmd *cobra.Command) {
 	}
 }
 
-func tryRunPluginHelp(dockerCli command.Cli, ccmd *cobra.Command, cargs []string) error {
-	root := ccmd.Root()
-
-	cmd, _, err := root.Traverse(cargs)
-	if err != nil {
-		return err
+func tryRunPluginHelp(dockerCli command.Cli, ccmd *cobra.Command) error {
+	if !pluginmanager.IsPluginCommand(ccmd) {
+		return errdefs.ErrNotFound
 	}
-	helpcmd, err := pluginmanager.PluginRunCommand(dockerCli, cmd.Name(), root)
+	helpcmd, err := pluginmanager.PluginRunCommand(dockerCli, ccmd.Name(), ccmd.Root())
 	if err != nil {
 		return err
 	}
@@ -251,8 +248,8 @@ func setHelpFunc(dockerCli command.Cli, cmd *cobra.Command) {
 			return
 		}
 
-		if len(args) >= 1 {
-			err := tryRunPluginHelp(dockerCli, ccmd, args)
+		if pluginmanager.IsPluginCommand(ccmd) {
+			err := tryRunPluginHelp(dockerCli, ccmd)
 			if err == nil {
 				return
 			}

cmd/docker/docker_test.go

@@ -7,6 +7,8 @@ import (
 	"fmt"
 	"io"
 	"os"
+	"path/filepath"
+	"strings"
 	"syscall"
 	"testing"
 	"time"
@@ -205,3 +207,39 @@ func TestVisitAll(t *testing.T) {
 	expected := []string{"sub1sub1", "sub1sub2", "sub1", "sub2", "root"}
 	assert.DeepEqual(t, expected, visited)
 }
+
+func TestSwarmInitHelpNotDelegatedToInitPlugin(t *testing.T) {
+	tmpDir := t.TempDir()
+	pluginScript := `#!/bin/sh
+if [ "$1" = "--help" ] || [ "$1" = "-h" ]; then
+	echo "PLUGIN INIT HELP"
+	exit 0
+fi
+printf '%s' '{"SchemaVersion":"0.1.0","ShortDescription":"Docker Init"}'
+`
+	pluginPath := filepath.Join(tmpDir, "docker-init")
+	err := os.WriteFile(pluginPath, []byte(pluginScript), 0o755)
+	assert.NilError(t, err)
+
+	var b bytes.Buffer
+	ctx := context.Background()
+	cli, err := command.NewDockerCli(
+		command.WithBaseContext(ctx),
+		command.WithCombinedStreams(&b),
+	)
+	assert.NilError(t, err)
+	cli.ConfigFile().CLIPluginsExtraDirs = []string{tmpDir}
+
+	tcmd := newDockerCommand(cli)
+	tcmd.SetArgs([]string{"swarm", "init", "--help"})
+	cmd, args, err := tcmd.HandleGlobalFlags()
+	assert.NilError(t, err)
+	assert.NilError(t, tcmd.Initialize())
+	cmd.SetArgs(args)
+	err = cmd.Execute()
+	assert.NilError(t, err)
+
+	out := b.String()
+	assert.Assert(t, is.Contains(out, "Initialize a swarm"))
+	assert.Assert(t, !strings.Contains(out, "PLUGIN INIT HELP"), "output: %s", out)
+}