refactor(internal/librarian/golang): reorganize module initialization functions (#4351)

This change improves the organization of the `golang` package by
grouping module-related functions together.
- Moved `modulePath` and `initModule` from `generate.go` to `module.go`.
- Moved `TestInitModule` from `generate_test.go` to `module_test.go`.
- Reordered the `Format` function within `generate.go` to appear earlier
in the file.

For #3617

Author: JoeWang1127

internal/librarian/golang/generate.go

@@ -55,6 +55,22 @@ func GenerateLibraries(ctx context.Context, libraries []*config.Library, googlea
 	return nil
 }
 
+// Format formats a generated Go library.
+func Format(ctx context.Context, library *config.Library) error {
+	outDir, err := filepath.Abs(library.Output)
+	if err != nil {
+		return err
+	}
+	args := []string{"-w", filepath.Join(outDir, library.Name)}
+	// TODO(https://github.com/googleapis/librarian/issues/4297), refactor this function
+	// to use import path.
+	snippetDir := snippetDirectory(outDir, library.Name)
+	if _, err := os.Stat(snippetDir); err == nil {
+		args = append(args, snippetDir)
+	}
+	return command.Run(ctx, "goimports", args...)
+}
+
 // generate generates a Go client library.
 func generate(ctx context.Context, library *config.Library, googleapisDir string) error {
 	if len(library.APIs) == 0 {
@@ -139,22 +155,6 @@ func generate(ctx context.Context, library *config.Library, googleapisDir string
 	return nil
 }
 
-// Format formats a generated Go library.
-func Format(ctx context.Context, library *config.Library) error {
-	outDir, err := filepath.Abs(library.Output)
-	if err != nil {
-		return err
-	}
-	args := []string{"-w", filepath.Join(outDir, library.Name)}
-	// TODO(https://github.com/googleapis/librarian/issues/4297), refactor this function
-	// to use import path.
-	snippetDir := snippetDirectory(outDir, library.Name)
-	if _, err := os.Stat(snippetDir); err == nil {
-		args = append(args, snippetDir)
-	}
-	return command.Run(ctx, "goimports", args...)
-}
-
 func generateAPI(ctx context.Context, api *config.API, library *config.Library, googleapisDir, outdir string) error {
 	goAPI := findGoAPI(library, api.Path)
 	if goAPI == nil {
@@ -282,16 +282,6 @@ func fixVersioning(outputDir, library, modPath string) error {
 	return nil
 }
 
-// modulePath returns the Go module path for the library. ModulePathVersion is
-// set for modules at v2+, e.g. "cloud.google.com/go/pubsub/v2".
-func modulePath(library *config.Library) string {
-	path := "cloud.google.com/go/" + library.Name
-	if library.Go != nil && library.Go.ModulePathVersion != "" {
-		path += "/" + library.Go.ModulePathVersion
-	}
-	return path
-}
-
 func collectProtoFiles(googleapisDir, apiPath string, nestedProtos []string) ([]string, error) {
 	apiDir := filepath.Join(googleapisDir, apiPath)
 	entries, err := os.ReadDir(apiDir)
@@ -392,15 +382,6 @@ func updateSnippetDirectory(baseDir, version string) error {
 	})
 }
 
-func initModule(ctx context.Context, dir, modPath string) error {
-	initArgs := []string{"go", "mod", "init", modPath}
-	if err := command.RunInDir(ctx, dir, initArgs[0], initArgs[1:]...); err != nil {
-		return err
-	}
-	tidyArgs := []string{"go", "mod", "tidy"}
-	return command.RunInDir(ctx, dir, tidyArgs[0], tidyArgs[1:]...)
-}
-
 // releaseLevel determines the release level for an API based on the API path and the library's current version.
 func releaseLevel(apiPath, version string) (string, error) {
 	apiVersion := filepath.Base(apiPath)

internal/librarian/golang/generate_test.go

@@ -16,7 +16,6 @@ package golang
 
 import (
 	"errors"
-	"io/fs"
 	"os"
 	"path/filepath"
 	"strings"
@@ -1080,22 +1079,3 @@ func TestBuildGAPICOpts(t *testing.T) {
 		})
 	}
 }
-
-func TestInitModule(t *testing.T) {
-	testhelper.RequireCommand(t, "go")
-	outDir := t.TempDir()
-	// Write an import so go mod tidy can generate a go.sum file.
-	content := []byte("package main\nimport _ \"golang.org/x/text\"\n")
-	if err := os.WriteFile(filepath.Join(outDir, "main.go"), content, 0644); err != nil {
-		t.Fatal(err)
-	}
-	if err := initModule(t.Context(), outDir, "example.com/testmod"); err != nil {
-		t.Fatal(err)
-	}
-	if _, err := os.Stat(filepath.Join(outDir, "go.mod")); errors.Is(err, fs.ErrNotExist) {
-		t.Errorf("go.mod does not exist")
-	}
-	if _, err := os.Stat(filepath.Join(outDir, "go.sum")); errors.Is(err, fs.ErrNotExist) {
-		t.Errorf("go.sum does not exist")
-	}
-}

internal/librarian/golang/module.go

@@ -15,11 +15,13 @@
 package golang
 
 import (
+	"context"
 	"errors"
 	"fmt"
 	"path/filepath"
 	"strings"
 
+	"github.com/googleapis/librarian/internal/command"
 	"github.com/googleapis/librarian/internal/config"
 	"github.com/googleapis/librarian/internal/serviceconfig"
 )
@@ -68,6 +70,24 @@ func findGoAPI(library *config.Library, apiPath string) *config.GoAPI {
 	return nil
 }
 
+// modulePath returns the Go module path for the library. ModulePathVersion is
+// set for modules at v2+, e.g. "cloud.google.com/go/pubsub/v2".
+func modulePath(library *config.Library) string {
+	path := "cloud.google.com/go/" + library.Name
+	if library.Go != nil && library.Go.ModulePathVersion != "" {
+		path += "/" + library.Go.ModulePathVersion
+	}
+	return path
+}
+
+// initModule initializes and tidies a Go module in the given directory.
+func initModule(ctx context.Context, dir, modPath string) error {
+	if err := command.RunInDir(ctx, dir, "go", "mod", "init", modPath); err != nil {
+		return err
+	}
+	return command.RunInDir(ctx, dir, "go", "mod", "tidy")
+}
+
 // defaultImportPathAndClientPkg returns the default Go import path and client package name
 // based on the provided API path.
 //

internal/librarian/golang/module_test.go

@@ -15,11 +15,13 @@
 package golang
 
 import (
+	"os"
 	"path/filepath"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
 	"github.com/googleapis/librarian/internal/config"
+	"github.com/googleapis/librarian/internal/testhelper"
 )
 
 func TestFill(t *testing.T) {
@@ -261,3 +263,22 @@ func TestSnippetDirectory(t *testing.T) {
 		t.Errorf("mismatch (-want +got):\n%s", diff)
 	}
 }
+
+func TestInitModule(t *testing.T) {
+	testhelper.RequireCommand(t, "go")
+	outDir := t.TempDir()
+	// Write an import so go mod tidy can generate a go.sum file.
+	content := []byte("package main\nimport _ \"golang.org/x/text\"\n")
+	if err := os.WriteFile(filepath.Join(outDir, "main.go"), content, 0644); err != nil {
+		t.Fatal(err)
+	}
+	if err := initModule(t.Context(), outDir, "example.com/testmod"); err != nil {
+		t.Fatal(err)
+	}
+	if _, err := os.Stat(filepath.Join(outDir, "go.mod")); err != nil {
+		t.Errorf("expected go.mod to exist, but Stat failed: %v", err)
+	}
+	if _, err := os.Stat(filepath.Join(outDir, "go.sum")); err != nil {
+		t.Errorf("expected go.sum to exist, but Stat failed: %v", err)
+	}
+}