feat(migrate): block legacylibrarian release and generate (#4612)

Modifies or adds entries to .librarian/config.yaml to to block
legacylibrarian generation and releasing of migrated libraries.

This loses comments from the config.yaml file, but after migration it
will be irrelevant anyway.

Fixes #4610

Author: jskeet

internal/legacylibrarian/legacyconfig/librarian_config.go

@@ -26,20 +26,20 @@ const (
 
 // LibrarianConfig defines the contract for the config.yaml file.
 type LibrarianConfig struct {
-	GlobalFilesAllowlist []*GlobalFile    `yaml:"global_files_allowlist"`
-	Libraries            []*LibraryConfig `yaml:"libraries"`
-	TagFormat            string           `yaml:"tag_format"`
+	GlobalFilesAllowlist []*GlobalFile    `yaml:"global_files_allowlist,omitempty"`
+	Libraries            []*LibraryConfig `yaml:"libraries,omitempty"`
+	TagFormat            string           `yaml:"tag_format,omitempty"`
 }
 
 // LibraryConfig defines configuration for a single library, identified by its ID.
 type LibraryConfig struct {
-	GenerateBlocked bool   `yaml:"generate_blocked"`
-	LibraryID       string `yaml:"id"`
-	NextVersion     string `yaml:"next_version"`
-	ReleaseBlocked  bool   `yaml:"release_blocked"`
-	TagFormat       string `yaml:"tag_format"`
+	GenerateBlocked bool   `yaml:"generate_blocked,omitempty"`
+	LibraryID       string `yaml:"id,omitempty"`
+	NextVersion     string `yaml:"next_version,omitempty"`
+	ReleaseBlocked  bool   `yaml:"release_blocked,omitempty"`
+	TagFormat       string `yaml:"tag_format,omitempty"`
 	// Whether to create a GitHub release for this library.
-	SkipGitHubReleaseCreation bool `yaml:"skip_github_release_creation"`
+	SkipGitHubReleaseCreation bool `yaml:"skip_github_release_creation,omitempty"`
 }
 
 // GlobalFile defines the global files in language repositories.

tool/cmd/migrate/legacylibrarian.go

@@ -109,6 +109,9 @@ func runLibrarianMigration(ctx context.Context, language string, repoPath string
 	if err := librarian.RunTidyOnConfig(ctx, repoPath, cfg); err != nil {
 		return errTidyFailed
 	}
+	if err := blockLegacyGenerationAndRelease(repoPath, cfg); err != nil {
+		return err
+	}
 	return nil
 }
 
@@ -120,12 +123,12 @@ func runCompleteCleanLibrarianMigration(ctx context.Context, language string, re
 		return nil, err
 	}
 
-	librarianConfig, err := readConfig(repoPath)
+	librarianConfig, err := readLegacyConfig(repoPath)
 	if err != nil {
 		return nil, err
 	}
 
-	repoConfig, err := readRepoConfig(repoPath)
+	repoConfig, err := readLegacyGoRepoConfig(repoPath)
 	if err != nil {
 		return nil, err
 	}
@@ -201,6 +204,40 @@ func buildConfigFromLibrarian(ctx context.Context, input *MigrationInput) (*conf
 	return cfg, nil
 }
 
+// blockLegacyGenerationAndRelease ensures that all libraries in the librarian
+// config have generation and release blocked in the legacy config, by rewriting
+// .librarian/config.yaml. This was previously a file maintained by hand, so a
+// comment line is added at the start. This function assumes that the current
+// directory is the repository root.
+func blockLegacyGenerationAndRelease(repoPath string, cfg *config.Config) error {
+	legacyConfig, err := readLegacyConfig(repoPath)
+	if err != nil {
+		return err
+	}
+	for _, lib := range cfg.Libraries {
+		legacyLib := legacyConfig.LibraryConfigFor(lib.Name)
+		if legacyLib == nil {
+			legacyLib = &legacyconfig.LibraryConfig{
+				LibraryID: lib.Name,
+			}
+			legacyConfig.Libraries = append(legacyConfig.Libraries, legacyLib)
+		}
+		legacyLib.GenerateBlocked = true
+		legacyLib.ReleaseBlocked = true
+	}
+	configYaml, err := yaml.Marshal(legacyConfig)
+	if err != nil {
+		return err
+	}
+	comment := "# This file is being migrated to librarian@latest, and is no longer maintained by hand.\n\n"
+	configYaml = append([]byte(comment), configYaml...)
+	configFile := filepath.Join(repoPath, librarianDir, librarianConfigFile)
+	if err := os.WriteFile(configFile, configYaml, 0644); err != nil {
+		return err
+	}
+	return nil
+}
+
 func fetchGoogleapis(ctx context.Context) (*config.Source, error) {
 	return fetchGoogleapisWithCommit(ctx, githubEndpoints, fetch.DefaultBranchMaster)
 }
@@ -453,17 +490,23 @@ func isEmptyGoGAPICInfo(info *goGAPICInfo) bool {
 		!info.NoMetadata
 }
 
+// readLegacyState reads the legacylibrarian state file for the given
+// repository root directory.
 func readState(path string) (*legacyconfig.LibrarianState, error) {
 	stateFile := filepath.Join(path, librarianDir, librarianStateFile)
 	return yaml.Read[legacyconfig.LibrarianState](stateFile)
 }
 
-func readConfig(path string) (*legacyconfig.LibrarianConfig, error) {
-	configFile := filepath.Join(path, librarianDir, librarianConfigFile)
+// readLegacyConfig reads the legacylibrarian configuration file for the given
+// repository root directory.
+func readLegacyConfig(repoPath string) (*legacyconfig.LibrarianConfig, error) {
+	configFile := filepath.Join(repoPath, librarianDir, librarianConfigFile)
 	return yaml.Read[legacyconfig.LibrarianConfig](configFile)
 }
 
-func readRepoConfig(path string) (*RepoConfig, error) {
+// readLegacyGoRepoConfig reads the legacylibrary Go-specific repository
+// configuration file for the given repository root directory.
+func readLegacyGoRepoConfig(path string) (*RepoConfig, error) {
 	configFile := filepath.Join(path, librarianDir, "generator-input/repo-config.yaml")
 	if _, err := os.Stat(configFile); err != nil {
 		if os.IsNotExist(err) {

tool/cmd/migrate/legacylibrarian_test.go

@@ -1058,7 +1058,7 @@ func TestReadRepoConfig(t *testing.T) {
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			got, err := readRepoConfig(test.repoPath)
+			got, err := readLegacyGoRepoConfig(test.repoPath)
 			if test.wantErr != nil {
 				if !errors.Is(err, test.wantErr) {
 					t.Errorf("expected error containing %q, got: %v", test.wantErr, err)
@@ -1158,6 +1158,92 @@ func TestToAPIs(t *testing.T) {
 	}
 }
 
+func TestBlockLegacyGenerationAndRelease(t *testing.T) {
+	tempDir := t.TempDir()
+	if err := os.Mkdir(filepath.Join(tempDir, librarianDir), 0755); err != nil {
+		t.Fatal(err)
+	}
+	originalConfig := &legacyconfig.LibrarianConfig{
+		TagFormat: "xyz",
+		Libraries: []*legacyconfig.LibraryConfig{
+			{
+				LibraryID: "not-migrated",
+			},
+			{
+				LibraryID:       "not-migrated-already-generate-blocked",
+				GenerateBlocked: true,
+			},
+			{
+				LibraryID:       "migrated-already-generate-blocked",
+				GenerateBlocked: true,
+			},
+			{
+				LibraryID:   "migrated",
+				NextVersion: "1.2.3",
+			},
+		},
+	}
+	configFile := filepath.Join(tempDir, librarianDir, librarianConfigFile)
+	if err := yaml.Write(configFile, originalConfig); err != nil {
+		t.Fatal(err)
+	}
+	migratedConfig := &config.Config{
+		Libraries: []*config.Library{
+			{Name: "migrated-already-generate-blocked"},
+			{Name: "not-previously-in-config"},
+			{Name: "migrated"},
+		},
+	}
+	if err := blockLegacyGenerationAndRelease(tempDir, migratedConfig); err != nil {
+		t.Fatal(err)
+	}
+	wantConfig := &legacyconfig.LibrarianConfig{
+		TagFormat: "xyz",
+		Libraries: []*legacyconfig.LibraryConfig{
+			{
+				LibraryID: "not-migrated",
+			},
+			{
+				LibraryID:       "not-migrated-already-generate-blocked",
+				GenerateBlocked: true,
+			},
+			{
+				LibraryID:       "migrated-already-generate-blocked",
+				GenerateBlocked: true,
+				ReleaseBlocked:  true,
+			},
+			{
+				LibraryID:       "migrated",
+				NextVersion:     "1.2.3",
+				GenerateBlocked: true,
+				ReleaseBlocked:  true,
+			},
+			{
+				LibraryID:       "not-previously-in-config",
+				GenerateBlocked: true,
+				ReleaseBlocked:  true,
+			},
+		},
+	}
+	gotConfig, err := readLegacyConfig(tempDir)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if diff := cmp.Diff(wantConfig, gotConfig); diff != "" {
+		t.Errorf("mismatch (-want +got):\n%s", diff)
+	}
+}
+
+func TestBlockLegacyGenerationAndRelease_Error(t *testing.T) {
+	tempDir := t.TempDir()
+	migratedConfig := &config.Config{}
+	gotErr := blockLegacyGenerationAndRelease(tempDir, migratedConfig)
+	wantErr := os.ErrNotExist
+	if !errors.Is(gotErr, wantErr) {
+		t.Errorf("blockLegacyGenerationAndRelease error = %v, wantErr %v", gotErr, wantErr)
+	}
+}
+
 func TestFetchGoogleapisWithCommit(t *testing.T) {
 	const (
 		wantCommit = "abcd123"