feat(tool/cmd/migrate): use googleapis_commitish from generation_config.yaml (#4514)

Librarian now uses the googleapis_commitish field from the Java
generation_config.yaml to fetch the specific version of googleapis used
during library generation.

Sample [librarian.yaml](https://paste.googleplex.com/5052837236178944)
produced with migrate in google-cloud-java.

For #4306

Author: zhumin8

tool/cmd/migrate/java.go

@@ -29,6 +29,10 @@ const (
 	generationConfigFileName = "generation_config.yaml"
 )
 
+var (
+	fetchSourceWithCommit = fetchGoogleapisWithCommit
+)
+
 type javaGAPICInfo struct {
 	NoRestNumericEnums bool
 	NoSamples          bool
@@ -119,19 +123,24 @@ type LibraryConfig struct {
 
 // GenerationConfig represents the root of generation_config.yaml.
 type GenerationConfig struct {
-	Libraries []LibraryConfig `yaml:"libraries"`
+	GoogleapisCommitish string          `yaml:"googleapis_commitish"`
+	Libraries           []LibraryConfig `yaml:"libraries"`
 }
 
 func runJavaMigration(ctx context.Context, repoPath string) error {
 	gen, err := readGenerationConfig(repoPath)
 	if err != nil {
 		return err
 	}
-	src, err := fetchSource(ctx)
+	commit := gen.GoogleapisCommitish
+	if commit == "" {
+		commit = "master"
+	}
+	src, err := fetchSourceWithCommit(ctx, commit)
 	if err != nil {
 		return errFetchSource
 	}
-	cfg := buildConfig(gen, src.Dir)
+	cfg := buildConfig(gen, src)
 	if cfg == nil {
 		return fmt.Errorf("no libraries found to migrate")
 	}
@@ -150,7 +159,7 @@ func readGenerationConfig(path string) (*GenerationConfig, error) {
 }
 
 // buildConfig converts a GenerationConfig to a Librarian Config.
-func buildConfig(gen *GenerationConfig, googleapisDir string) *config.Config {
+func buildConfig(gen *GenerationConfig, src *config.Source) *config.Config {
 	var libs []*config.Library
 	for _, l := range gen.Libraries {
 		name := l.LibraryName
@@ -165,7 +174,7 @@ func buildConfig(gen *GenerationConfig, googleapisDir string) *config.Config {
 			}
 			apis = append(apis, &config.API{Path: g.ProtoPath})
 
-			info, err := parseJavaBazel(googleapisDir, g.ProtoPath)
+			info, err := parseJavaBazel(src.Dir, g.ProtoPath)
 			if err != nil {
 				log.Printf("Warning: failed to parse BUILD.bazel for %s: %v", g.ProtoPath, err)
 				continue
@@ -218,7 +227,7 @@ func buildConfig(gen *GenerationConfig, googleapisDir string) *config.Config {
 		Language: "java",
 		Default:  &config.Default{},
 		Sources: &config.Sources{
-			Googleapis: &config.Source{Dir: googleapisDir},
+			Googleapis: src,
 		},
 		Libraries: libs,
 		Repo:      "googleapis/google-cloud-java",

tool/cmd/migrate/java_test.go

@@ -25,9 +25,9 @@ import (
 )
 
 func TestRunJavaMigration(t *testing.T) {
-	fetchSource = func(ctx context.Context) (*config.Source, error) {
+	fetchSourceWithCommit = func(ctx context.Context, commitish string) (*config.Source, error) {
 		return &config.Source{
-			Commit: "abcd123",
+			Commit: commitish,
 			SHA256: "sha123",
 			Dir:    "../../internal/testdata/googleapis",
 		}, nil
@@ -265,7 +265,7 @@ func TestBuildConfig(t *testing.T) {
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			got := buildConfig(test.gen, "../../internal/testdata/googleapis")
+			got := buildConfig(test.gen, &config.Source{Dir: "../../internal/testdata/googleapis"})
 			if diff := cmp.Diff(test.want, got); diff != "" {
 				t.Errorf("mismatch (-want +got):\n%s", diff)
 			}

tool/cmd/migrate/legacylibrarian.go

@@ -177,27 +177,31 @@ func buildConfigFromLibrarian(ctx context.Context, input *MigrationInput) (*conf
 }
 
 func fetchGoogleapis(ctx context.Context) (*config.Source, error) {
+	return fetchGoogleapisWithCommit(ctx, fetch.DefaultBranchMaster)
+}
+
+func fetchGoogleapisWithCommit(ctx context.Context, commitish string) (*config.Source, error) {
 	endpoint := &fetch.Endpoints{
 		API:      "https://api.github.com",
 		Download: "https://github.com",
 	}
 	repo := &fetch.Repo{
 		Org:    "googleapis",
 		Repo:   "googleapis",
-		Branch: fetch.DefaultBranchMaster,
+		Branch: commitish,
 	}
-	latestCommit, sha256, err := fetch.LatestCommitAndChecksum(endpoint, repo)
+	commit, sha256, err := fetch.LatestCommitAndChecksum(endpoint, repo)
 	if err != nil {
 		return nil, err
 	}
 
-	dir, err := fetch.RepoDir(ctx, googleapisRepo, latestCommit, sha256)
+	dir, err := fetch.RepoDir(ctx, googleapisRepo, commit, sha256)
 	if err != nil {
 		return nil, err
 	}
 
 	return &config.Source{
-		Commit: latestCommit,
+		Commit: commit,
 		SHA256: sha256,
 		Dir:    dir,
 	}, nil