feat(internal/librarian): identify nodejs veneer libraries (#4802)

isVeneer function is updated to return true for Node.js libraries that
have an output path specified but no APIs defined. This ensures that
Librarian can correctly categorize handwritten Node.js libraries that do
not contain generated GAPIC surfaces.

Author: julieqiu

internal/librarian/library.go

@@ -164,10 +164,14 @@ func mergePackageDependencies(defaults, lib []*config.RustPackageDependency) []*
 // isVeneer reports whether the library has handwritten code wrapping generated
 // code.
 func isVeneer(language string, lib *config.Library) bool {
-	if language == config.LanguageRust {
+	switch language {
+	case config.LanguageRust:
 		return rust.IsVeneer(lib)
+	case config.LanguageNodejs:
+		return lib.Output != "" && len(lib.APIs) == 0
+	default:
+		return false
 	}
-	return false
 }
 
 // libraryOutput returns the output path for a library. If the library has an

internal/librarian/library_test.go

@@ -591,3 +591,53 @@ func TestCanDeriveAPIPath(t *testing.T) {
 		})
 	}
 }
+
+func TestIsVeneer(t *testing.T) {
+	for _, test := range []struct {
+		name     string
+		language string
+		lib      *config.Library
+		want     bool
+	}{
+		{
+			name:     "rust is veneer",
+			language: config.LanguageRust,
+			lib: &config.Library{
+				Rust: &config.RustCrate{
+					Modules: []*config.RustModule{{APIPath: "google/storage/v2"}},
+				},
+			},
+			want: true,
+		},
+		{
+			name:     "rust is not veneer",
+			language: config.LanguageRust,
+			lib:      &config.Library{},
+			want:     false,
+		},
+		{
+			name:     "nodejs handwritten tool is veneer",
+			language: config.LanguageNodejs,
+			lib: &config.Library{
+				Output: "packages/typeless-sample-bot",
+				APIs:   nil,
+			},
+			want: true,
+		},
+		{
+			name:     "nodejs gapic lib is not veneer",
+			language: config.LanguageNodejs,
+			lib: &config.Library{
+				Output: "packages/gapic-lib",
+				APIs:   []*config.API{{Path: "google/example/v1"}},
+			},
+			want: false,
+		},
+	} {
+		t.Run(test.name, func(t *testing.T) {
+			if got := isVeneer(test.language, test.lib); got != test.want {
+				t.Errorf("isVeneer(%q, %+v) = %v, want %v", test.language, test.lib, got, test.want)
+			}
+		})
+	}
+}