feat(helm): add --allow-empty flag to 'helm repo list'

`--allow-empty` flag signal that it is ok (return exit code 0)
to not have any repositories to show.

Closes #10028

Signed-off-by: Piotr Resztak <piotr.resztak@gmail.com>

cmd/helm/repo_list.go

@@ -30,8 +30,15 @@ import (
 	"helm.sh/helm/v3/pkg/repo"
 )
 
+type repoListOptions struct {
+	allowEmpty   bool
+	repoFile     string
+	outputFormat output.Format
+}
+
 func newRepoListCmd(out io.Writer) *cobra.Command {
-	var outfmt output.Format
+	o := &repoListOptions{}
+
 	cmd := &cobra.Command{
 		Use:               "list",
 		Aliases:           []string{"ls"},
@@ -39,20 +46,29 @@ func newRepoListCmd(out io.Writer) *cobra.Command {
 		Args:              require.NoArgs,
 		ValidArgsFunction: noCompletions,
 		RunE: func(cmd *cobra.Command, args []string) error {
-			f, err := repo.LoadFile(settings.RepositoryConfig)
-			if isNotExist(err) || (len(f.Repositories) == 0 && !(outfmt == output.JSON || outfmt == output.YAML)) {
-				return errors.New("no repositories to show")
-			}
-
-			return outfmt.Write(out, &repoListWriter{f.Repositories})
+			o.repoFile = settings.RepositoryConfig
+			return o.run(out)
 		},
 	}
 
-	bindOutputFlag(cmd, &outfmt)
+	f := cmd.Flags()
+	f.BoolVar(&o.allowEmpty, "allow-empty", false, "exit with status 0 and no error message if no repositories to show")
+	bindOutputFlag(cmd, &o.outputFormat)
 
 	return cmd
 }
 
+func (o *repoListOptions) run(out io.Writer) error {
+	f, err := repo.LoadFile(o.repoFile)
+	if o.allowEmpty {
+		return o.outputFormat.Write(out, &repoListWriter{f.Repositories})
+	}
+	if isNotExist(err) || (len(f.Repositories) == 0 && !(o.outputFormat == output.JSON || o.outputFormat == output.YAML)) {
+		return errors.New("no repositories to show")
+	}
+	return o.outputFormat.Write(out, &repoListWriter{f.Repositories})
+}
+
 type repositoryElement struct {
 	Name string `json:"name"`
 	URL  string `json:"url"`

cmd/helm/repo_list_test.go

@@ -17,7 +17,12 @@ limitations under the License.
 package main
 
 import (
+	"os"
+	"path/filepath"
 	"testing"
+
+	"helm.sh/helm/v3/pkg/cli/output"
+	"helm.sh/helm/v3/pkg/repo/repotest"
 )
 
 func TestRepoListOutputCompletion(t *testing.T) {
@@ -27,3 +32,35 @@ func TestRepoListOutputCompletion(t *testing.T) {
 func TestRepoListFileCompletion(t *testing.T) {
 	checkFileCompletion(t, "repo list", false)
 }
+
+func TestRepoListAllowEmpty(t *testing.T) {
+	ts, err := repotest.NewTempServerWithCleanup(t, "testdata/testserver/*.*")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer ts.Stop()
+
+	rootDir := ts.Root()
+	repoFile := filepath.Join(rootDir, "repositories.yaml")
+
+	// Remove existing repo
+	const testRepoName = "test"
+
+	rmOpts := repoRemoveOptions{
+		names:     []string{testRepoName},
+		repoFile:  repoFile,
+		repoCache: rootDir,
+	}
+	if err := rmOpts.run(os.Stderr); err != nil {
+		t.Error(err)
+	}
+
+	listOpts := repoListOptions{
+		allowEmpty:   true,
+		repoFile:     repoFile,
+		outputFormat: output.Table,
+	}
+	if err := listOpts.run(os.Stderr); err != nil {
+		t.Error("Error not expected when listing repositories with allow-empty flag")
+	}
+}