fix(internal/librarian): add cargo update --workspace to run after generate all (#3711)

Add `cargo update --workspace` to run inside of `librarian generate
--all`. Add as a postGenerate step to generate, to perform repo level
actions after generating individual libraries.

For #3683

Author: zhumin8

internal/librarian/fake.go

@@ -61,6 +61,10 @@ func fakeFormat(library *config.Library) error {
 	return os.WriteFile(readmePath, []byte(formatted), 0644)
 }
 
+func fakePostGenerate() error {
+	return os.WriteFile("POST_GENERATE_README.md", []byte("PostGenerated\n"), 0644)
+}
+
 func fakePublish(libraries []string, execute bool) error {
 	content := fmt.Sprintf("libraries=%s; execute=%v",
 		strings.Join(libraries, ","), execute)

internal/librarian/generate.go

@@ -151,7 +151,20 @@ func generateAll(ctx context.Context, cfg *config.Config) error {
 			return err
 		}
 	}
-	return nil
+	return postGenerate(ctx, cfg.Language)
+}
+
+// postGenerate performs repository-level actions after all individual
+// libraries have been generated.
+func postGenerate(ctx context.Context, language string) error {
+	switch language {
+	case languageRust:
+		return rust.UpdateWorkspace(ctx)
+	case languageFake:
+		return fakePostGenerate()
+	default:
+		return nil
+	}
 }
 
 func defaultOutput(language, channel, defaultOut string) string {

internal/librarian/generate_test.go

@@ -48,10 +48,11 @@ func TestGenerateCommand(t *testing.T) {
 	}
 
 	for _, test := range []struct {
-		name    string
-		args    []string
-		wantErr error
-		want    []string
+		name             string
+		args             []string
+		wantErr          error
+		want             []string
+		wantPostGenerate bool
 	}{
 		{
 			name:    "no args",
@@ -69,9 +70,10 @@ func TestGenerateCommand(t *testing.T) {
 			want: []string{lib1},
 		},
 		{
-			name: "all flag",
-			args: []string{"librarian", "generate", "--all"},
-			want: []string{lib1, lib2},
+			name:             "all flag",
+			args:             []string{"librarian", "generate", "--all"},
+			want:             []string{lib1, lib2},
+			wantPostGenerate: true,
 		},
 		{
 			name: "skip generate",
@@ -161,6 +163,13 @@ libraries:
 					t.Errorf("mismatch for STARTER.md for %q (-want +got):\n%s", libName, diff)
 				}
 			}
+
+			if test.wantPostGenerate {
+				postGeneratePath := filepath.Join(tempDir, "POST_GENERATE_README.md")
+				if _, err := os.Stat(postGeneratePath); err != nil {
+					t.Errorf("expected POST_GENERATE_README.md to exist, but got error: %v", err)
+				}
+			}
 		})
 	}
 }

internal/librarian/rust/generate.go

@@ -77,6 +77,11 @@ func Generate(ctx context.Context, library *config.Library, sources *Sources) er
 	return nil
 }
 
+// UpdateWorkspace updates dependencies for the entire Rust workspace.
+func UpdateWorkspace(ctx context.Context) error {
+	return command.Run(ctx, "cargo", "update", "--workspace")
+}
+
 // Format formats a generated Rust library. Must be called sequentially;
 // parallel calls cause race conditions as cargo fmt runs cargo metadata,
 // which competes for locks on the workspace Cargo.toml and Cargo.lock.