fix(devtools/cmd/migrate-librarian): make repo path a positional arg (#3187)

The repo path is now a positional argument instead of a -repo flag,
allowing usage like `migrate-librarian .` instead of `migrate-librarian
-repo .`.

The deriveLanguage function now converts the path to an absolute path
before checking if it ends with "go" or "python", enabling it to work
correctly with relative paths like ".".

Author: julieqiu

devtools/cmd/migrate-librarian/main.go

@@ -43,9 +43,9 @@ const (
 )
 
 var (
-	errRepoNotFound     = errors.New("-repo flag is required")
-	errLangNotSupported = errors.New("only go and python are supported")
 	errFetchSource      = errors.New("cannot fetch source")
+	errLangNotSupported = errors.New("only go and python are supported")
+	errRepoNotFound     = errors.New("exactly one repo path argument is required")
 	errTidyFailed       = errors.New("librarian tidy failed")
 
 	fetchSource = fetchGoogleapis
@@ -60,27 +60,26 @@ func main() {
 
 func run(ctx context.Context, args []string) error {
 	flagSet := flag.NewFlagSet("migrate-librarian", flag.ContinueOnError)
-	repoPath := flagSet.String("repo", "",
-		"Path to the repository containing legacy .librarian configuration (required). Must end with go or python.")
 	outputPath := flagSet.String("output", "./librarian.yaml", "Output file path (default: ./librarian.yaml)")
 	if err := flagSet.Parse(args); err != nil {
 		return err
 	}
-	if *repoPath == "" {
+	if flagSet.NArg() != 1 {
 		return errRepoNotFound
 	}
+	repoPath := flagSet.Arg(0)
 
-	language, err := deriveLanguage(*repoPath)
+	language, err := deriveLanguage(repoPath)
 	if err != nil {
 		return err
 	}
 
-	librarianState, err := readState(*repoPath)
+	librarianState, err := readState(repoPath)
 	if err != nil {
 		return err
 	}
 
-	librarianConfig, err := readConfig(*repoPath)
+	librarianConfig, err := readConfig(repoPath)
 	if err != nil {
 		return err
 	}
@@ -102,15 +101,15 @@ func run(ctx context.Context, args []string) error {
 }
 
 func deriveLanguage(repoPath string) (string, error) {
-	if strings.HasSuffix(repoPath, "go") {
+	base := filepath.Base(repoPath)
+	switch {
+	case strings.HasSuffix(base, "go"):
 		return "go", nil
-	}
-
-	if strings.HasSuffix(repoPath, "python") {
+	case strings.HasSuffix(base, "python"):
 		return "python", nil
+	default:
+		return "", errLangNotSupported
 	}
-
-	return "", errLangNotSupported
 }
 
 func buildConfig(

devtools/cmd/migrate-librarian/main_test.go

@@ -36,7 +36,6 @@ func TestRunMigrateLibrarian(t *testing.T) {
 	for _, test := range []struct {
 		name     string
 		repoPath string
-		lang     string
 		wantErr  error
 	}{
 		{
@@ -69,10 +68,9 @@ func TestRunMigrateLibrarian(t *testing.T) {
 				}
 			})
 
-			args := []string{"-repo", test.repoPath, "-output", outputPath}
-
-			if test.lang != "" {
-				args = append(args, "-lang", test.lang)
+			args := []string{"-output", outputPath}
+			if test.repoPath != "" {
+				args = append(args, test.repoPath)
 			}
 
 			if err := run(t.Context(), args); err != nil {