refactor(devtools/cmd/migrate-sidekick): change repo from flag to arg (#3186)

The repo path is now passed as the first positional argument instead of
using the -repo flag. This simplifies the command usage to
`migrate-sidekick .` when running inside google-cloud-rust, since repo
is a required path.

Author: julieqiu

devtools/cmd/migrate-sidekick/main.go

@@ -37,7 +37,7 @@ const (
 )
 
 var (
-	errRepoNotFound     = errors.New("-repo flag is required")
+	errRepoNotFound     = errors.New("repo path argument is required")
 	errSidekickNotFound = errors.New(".sidekick.toml not found")
 	errSrcNotFound      = errors.New("src/generated directory not found")
 	errTidyFailed       = errors.New("librarian tidy failed")
@@ -81,26 +81,26 @@ func main() {
 
 func run(args []string) error {
 	flagSet := flag.NewFlagSet("migrate-sidekick", flag.ContinueOnError)
-	repoPath := flagSet.String("repo", "", "Path to the google-cloud-rust repository (required)")
 	outputPath := flagSet.String("output", "./librarian.yaml", "Output file path (default: ./librarian.yaml)")
-	if err := flagSet.Parse(args[1:]); err != nil {
+	if err := flagSet.Parse(args); err != nil {
 		return err
 	}
 
-	if *repoPath == "" {
+	if flagSet.NArg() < 1 {
 		return errRepoNotFound
 	}
+	repoPath := flagSet.Arg(0)
 
 	slog.Info("Reading sidekick.toml...", "path", repoPath)
 
 	// Read root .sidekick.toml for defaults
-	defaults, err := readRootSidekick(*repoPath)
+	defaults, err := readRootSidekick(repoPath)
 	if err != nil {
 		return fmt.Errorf("failed to read root .sidekick.toml: %w", err)
 	}
 
 	// Find all .sidekick.toml files
-	sidekickFiles, err := findSidekickFiles(*repoPath)
+	sidekickFiles, err := findSidekickFiles(repoPath)
 	if err != nil {
 		return fmt.Errorf("failed to find sidekick.toml files: %w", err)
 	}

devtools/cmd/migrate-sidekick/main_test.go

@@ -436,7 +436,7 @@ func TestRunMigrateCommand(t *testing.T) {
 				}
 			})
 
-			if err := run([]string{"migrate-sidekick", "-repo", test.path}); err != nil {
+			if err := run([]string{test.path}); err != nil {
 				if test.wantErr == nil {
 					t.Fatal(err)
 				}