feat(internal/librarian/golang): set default library name for Go (#5191)

The default library name for Go is now derived by stripping common API
prefixes such as `google/cloud/`, `google/api/`, and `google/devtools/`.
This ensures that the resulting library names are consistent with the Go
client library conventions.

A mapping is introduced to handle special cases like `maps` and
`shopping`, where all related APIs are grouped into a single library.
For other APIs, the name is derived from the first segment of the path
after the known prefixes.

Fixes #4996

Author: JoeWang1127

internal/librarian/golang/module.go

@@ -28,7 +28,10 @@ import (
 
 const (
 	// rootModule is the name of the root module in the configuration.
-	rootModule = "root-module"
+	rootModule        = "root-module"
+	apiPrefix         = "google/api/"
+	cloudAPIPrefix    = "google/cloud/"
+	devtoolsAPIPrefix = "google/devtools/"
 )
 
 var (
@@ -78,16 +81,23 @@ func Fill(library *config.Library) (*config.Library, error) {
 	return library, nil
 }
 
-// DefaultLibraryName derives a default library name from an API path.
-// For a versioned API path, it returns the service name. For a non-versioned
-// API path, it returns the last path segment.
+// DefaultLibraryName derives a default library name from an API path by stripping
+// known prefixes (e.g., "google/cloud/", "google/api/") and returning the first
+// segment of the remaining path.
 func DefaultLibraryName(api string) string {
-	path := api
-	if serviceconfig.ExtractVersion(api) != "" {
-		// Strip version suffix (v1, v1beta2, v2alpha, etc.).
-		path = filepath.Dir(api)
+	api = strings.TrimPrefix(api, cloudAPIPrefix)
+	// Some non-cloud APIs, e.g., google/api, google/devtools/, etc., create one library
+	// per API. The resulting library configurations need to set additional configurations,
+	// e.g., import_path, for the generation to work.
+	// We don't infer the configuration here and let the user set the configurations manually.
+	api = strings.TrimPrefix(api, apiPrefix)
+	api = strings.TrimPrefix(api, devtoolsAPIPrefix)
+	api = strings.TrimPrefix(api, "google/")
+	idx := strings.Index(api, "/")
+	if idx == -1 {
+		return api
 	}
-	return filepath.Base(path)
+	return api[:idx]
 }
 
 // DefaultOutput returns the default output directory for a Go library.

internal/librarian/golang/module_test.go

@@ -612,14 +612,39 @@ func TestDefaultLibraryName(t *testing.T) {
 		want string
 	}{
 		{
-			name: "versioned api",
+			name: "cloud API",
 			api:  "google/cloud/secretmanager/v1",
 			want: "secretmanager",
 		},
 		{
-			name: "non versioned api",
+			name: "devtools API",
+			api:  "google/devtools/artifactregistry/v1",
+			want: "artifactregistry",
+		},
+		{
+			name: "google/api API",
+			api:  "google/api/cloudquotas/v1",
+			want: "cloudquotas",
+		},
+		{
+			name: "maps API",
+			api:  "google/maps/geocode/v4",
+			want: "maps",
+		},
+		{
+			name: "other API",
+			api:  "google/other/v4",
+			want: "other",
+		},
+		{
+			name: "shopping API",
 			api:  "google/shopping/type",
-			want: "type",
+			want: "shopping",
+		},
+		{
+			name: "non existent API",
+			api:  "google/random",
+			want: "random",
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {