Add completion support for kubectl plugins

This commit allows us to get shell completion for kubectl plugins.

For example, with the use of a plugin named 'kubectl-krew', completing
   kubectl k<tab>
will include 'krew' in the list of possible completions.

Because the shell completion scripts are generated by Cobra, this commit
took the approach of registering every plugin as a Cobra command.  This
makes Cobra aware of each plugin command when generating completions.

For efficiency, searching for plugins and registering them as Cobra
commands is only done when needed, which is when calling the
'kubectl completion' command in the case of bash, as it includes all
commands and subcommands directly in the bash generated script.

For the other shells, this will need to be done for the
'kubectl __complete' command, in a follow-up command.

Co-authored-by: Marc Khouzam <marc.khouzam@montreal.ca>
Signed-off-by: Kazuki Suda <kazuki.suda@gmail.com>

staging/src/k8s.io/kubectl/pkg/cmd/completion/completion.go

@@ -17,11 +17,17 @@ limitations under the License.
 package completion
 
 import (
+	"bytes"
 	"fmt"
 	"io"
+	"io/ioutil"
+	"path/filepath"
+	"strings"
 
 	"github.com/spf13/cobra"
 
+	"k8s.io/cli-runtime/pkg/genericclioptions"
+	"k8s.io/kubectl/pkg/cmd/plugin"
 	cmdutil "k8s.io/kubectl/pkg/cmd/util"
 	"k8s.io/kubectl/pkg/util/i18n"
 	"k8s.io/kubectl/pkg/util/templates"
@@ -155,6 +161,7 @@ func RunCompletion(out io.Writer, boilerPlate string, cmd *cobra.Command, args [
 	if !found {
 		return cmdutil.UsageErrorf(cmd, "Unsupported shell type %q.", args[0])
 	}
+	addPluginCommands(cmd.Root())
 
 	return run(out, boilerPlate, cmd.Parent())
 }
@@ -206,3 +213,47 @@ func runCompletionPwsh(out io.Writer, boilerPlate string, kubectl *cobra.Command
 
 	return kubectl.GenPowerShellCompletionWithDesc(out)
 }
+
+// addPluginCommand adds plugin commands under the given command so that
+// completion includes them
+func addPluginCommands(kubectl *cobra.Command) {
+	streams := genericclioptions.IOStreams{
+		In:     &bytes.Buffer{},
+		Out:    ioutil.Discard,
+		ErrOut: ioutil.Discard,
+	}
+
+	o := &plugin.PluginListOptions{IOStreams: streams}
+	o.Complete(kubectl)
+	plugins, _ := o.ListPlugins()
+
+	for _, plugin := range plugins {
+		plugin = filepath.Base(plugin)
+		args := []string{}
+
+		// Plugins are named "kubectl-<name>" or with more - such as
+		// "kubectl-<name>-<subcmd1>..."
+		for _, arg := range strings.Split(plugin, "-")[1:] {
+			// Underscores (_) in plugin's filename are replaced with dashes(-)
+			// e.g. foo_bar -> foo-bar
+			args = append(args, strings.Replace(arg, "_", "-", -1))
+		}
+
+		// In order to avoid that the same plugin command is added,
+		// find the lowest command given args from the root command
+		parentCmd, remainingArgs, _ := kubectl.Find(args)
+		if parentCmd == nil {
+			parentCmd = kubectl
+		}
+
+		for _, remainingArg := range remainingArgs {
+			cmd := &cobra.Command{
+				Use: remainingArg,
+				// A Run is required for it to be a valid command
+				Run: func(cmd *cobra.Command, args []string) {},
+			}
+			parentCmd.AddCommand(cmd)
+			parentCmd = cmd
+		}
+	}
+}

staging/src/k8s.io/kubectl/pkg/cmd/plugin/plugin.go

@@ -115,58 +115,27 @@ func (o *PluginListOptions) Complete(cmd *cobra.Command) error {
 }
 
 func (o *PluginListOptions) Run() error {
-	pluginsFound := false
+	plugins, pluginErrors := o.ListPlugins()
-	isFirstFile := true
-	pluginErrors := []error{}
-	pluginWarnings := 0
 
-	for _, dir := range uniquePathsList(o.PluginPaths) {
+	if len(plugins) > 0 {
-		if len(strings.TrimSpace(dir)) == 0 {
+		fmt.Fprintf(o.Out, "The following compatible plugins are available:\n\n")
-			continue
+	} else {
-		}
+		pluginErrors = append(pluginErrors, fmt.Errorf("error: unable to find any kubectl plugins in your PATH"))
-
-		files, err := ioutil.ReadDir(dir)
-		if err != nil {
-			if _, ok := err.(*os.PathError); ok {
-				fmt.Fprintf(o.ErrOut, "Unable to read directory %q from your PATH: %v. Skipping...\n", dir, err)
-				continue
-			}
-
-			pluginErrors = append(pluginErrors, fmt.Errorf("error: unable to read directory %q in your PATH: %v", dir, err))
-			continue
-		}
-
-		for _, f := range files {
-			if f.IsDir() {
-				continue
-			}
-			if !hasValidPrefix(f.Name(), ValidPluginFilenamePrefixes) {
-				continue
-			}
-
-			if isFirstFile {
-				fmt.Fprintf(o.Out, "The following compatible plugins are available:\n\n")
-				pluginsFound = true
-				isFirstFile = false
-			}
-
-			pluginPath := f.Name()
-			if !o.NameOnly {
-				pluginPath = filepath.Join(dir, pluginPath)
-			}
-
-			fmt.Fprintf(o.Out, "%s\n", pluginPath)
-			if errs := o.Verifier.Verify(filepath.Join(dir, f.Name())); len(errs) != 0 {
-				for _, err := range errs {
-					fmt.Fprintf(o.ErrOut, "  - %s\n", err)
-					pluginWarnings++
-				}
-			}
-		}
 	}
 
-	if !pluginsFound {
+	pluginWarnings := 0
-		pluginErrors = append(pluginErrors, fmt.Errorf("error: unable to find any kubectl plugins in your PATH"))
+	for _, pluginPath := range plugins {
+		if o.NameOnly {
+			fmt.Fprintf(o.Out, "%s\n", filepath.Base(pluginPath))
+		} else {
+			fmt.Fprintf(o.Out, "%s\n", pluginPath)
+		}
+		if errs := o.Verifier.Verify(pluginPath); len(errs) != 0 {
+			for _, err := range errs {
+				fmt.Fprintf(o.ErrOut, "  - %s\n", err)
+				pluginWarnings++
+			}
+		}
 	}
 
 	if pluginWarnings > 0 {
@@ -187,6 +156,42 @@ func (o *PluginListOptions) Run() error {
 	return nil
 }
 
+// ListPlugins returns list of plugin paths.
+func (o *PluginListOptions) ListPlugins() ([]string, []error) {
+	plugins := []string{}
+	errors := []error{}
+
+	for _, dir := range uniquePathsList(o.PluginPaths) {
+		if len(strings.TrimSpace(dir)) == 0 {
+			continue
+		}
+
+		files, err := ioutil.ReadDir(dir)
+		if err != nil {
+			if _, ok := err.(*os.PathError); ok {
+				fmt.Fprintf(o.ErrOut, "Unable to read directory %q from your PATH: %v. Skipping...\n", dir, err)
+				continue
+			}
+
+			errors = append(errors, fmt.Errorf("error: unable to read directory %q in your PATH: %v", dir, err))
+			continue
+		}
+
+		for _, f := range files {
+			if f.IsDir() {
+				continue
+			}
+			if !hasValidPrefix(f.Name(), ValidPluginFilenamePrefixes) {
+				continue
+			}
+
+			plugins = append(plugins, filepath.Join(dir, f.Name()))
+		}
+	}
+
+	return plugins, errors
+}
+
 // pathVerifier receives a path and determines if it is valid or not
 type PathVerifier interface {
 	// Verify determines if a given path is valid

staging/src/k8s.io/kubectl/pkg/cmd/plugin/plugin_test.go

@@ -20,6 +20,8 @@ import (
 	"fmt"
 	"io/ioutil"
 	"os"
+	"path/filepath"
+	"reflect"
 	"strings"
 	"testing"
 
@@ -178,6 +180,34 @@ func TestPluginPathsAreValid(t *testing.T) {
 	}
 }
 
+func TestListPlugins(t *testing.T) {
+	pluginPath, _ := filepath.Abs("./testdata")
+	expectPlugins := []string{
+		filepath.Join(pluginPath, "kubectl-foo"),
+		filepath.Join(pluginPath, "kubectl-version"),
+	}
+
+	verifier := newFakePluginPathVerifier()
+	ioStreams, _, _, _ := genericclioptions.NewTestIOStreams()
+	pluginPaths := []string{pluginPath}
+
+	o := &PluginListOptions{
+		Verifier:  verifier,
+		IOStreams: ioStreams,
+
+		PluginPaths: pluginPaths,
+	}
+
+	plugins, errs := o.ListPlugins()
+	if len(errs) > 0 {
+		t.Fatalf("unexpected errors: %v", errs)
+	}
+
+	if !reflect.DeepEqual(expectPlugins, plugins) {
+		t.Fatalf("saw unexpected plugins. Expecting %v, got %v", expectPlugins, plugins)
+	}
+}
+
 type duplicatePathError struct {
 	path string
 }