feat(internal/librarian/golang): support configurable tool dependencies in librarian.yaml

doc/config-schema.md

@@ -57,6 +57,7 @@ This document describes the schema for the librarian.yaml.
 | `cargo` | list of [CargoTool](#cargotool-configuration) (optional) | Defines tools to install via cargo. |
 | `npm` | list of [NPMTool](#npmtool-configuration) (optional) | Defines tools to install via npm. |
 | `pip` | list of [PipTool](#piptool-configuration) (optional) | Defines tools to install via pip. |
+| `go` | list of [GoTool](#gotool-configuration) (optional) | Defines tools to install via go. |
 
 ## CargoTool Configuration
 
@@ -83,6 +84,13 @@ This document describes the schema for the librarian.yaml.
 | `version` | string | Is the version to install. |
 | `package` | string | Is the pip install specifier (e.g., "pkg@git+https://..."). |
 
+## GoTool Configuration
+
+| Field | Type | Description |
+| :--- | :--- | :--- |
+| `name` | string | Is the go module name. |
+| `version` | string | Is the version to install. |
+
 ## Default Configuration
 
 | Field | Type | Description |

internal/config/config.go

@@ -136,6 +136,9 @@ type Tools struct {
 
 	// Pip defines tools to install via pip.
 	Pip []*PipTool `yaml:"pip,omitempty"`
+
+	// Go defines tools to install via go.
+	Go []*GoTool `yaml:"go,omitempty"`
 }
 
 // CargoTool defines a tool to install via cargo.
@@ -177,6 +180,15 @@ type PipTool struct {
 	Package string `yaml:"package,omitempty"`
 }
 
+// GoTool defines a tool to install via go.
+type GoTool struct {
+	// Name is the go module name.
+	Name string `yaml:"name"`
+
+	// Version is the version to install.
+	Version string `yaml:"version,omitempty"`
+}
+
 // Default contains default settings for all libraries.
 type Default struct {
 	// Keep lists files and directories to preserve during regeneration.

internal/librarian/generate.go

@@ -201,7 +201,7 @@ func generateLibraries(ctx context.Context, cfg *config.Config, libraries []*con
 		g, gctx = errgroup.WithContext(ctx)
 		for _, library := range libraries {
 			g.Go(func() error {
-				if err := golang.Format(gctx, library); err != nil {
+				if err := golang.Format(gctx, library, cfg.Tools); err != nil {
 					return fmt.Errorf("format library %q (%s): %w", library.Name, cfg.Language, err)
 				}
 				return nil

internal/librarian/golang/format.go

@@ -23,7 +23,7 @@ import (
 )
 
 // Format formats a generated Go library.
-func Format(ctx context.Context, library *config.Library) error {
+func Format(ctx context.Context, library *config.Library, tools *config.Tools) error {
 	// No need to format the root module because it does not
 	// have generated code.
 	if library.Name == rootModule {
@@ -33,6 +33,7 @@ func Format(ctx context.Context, library *config.Library) error {
 	if err != nil {
 		return err
 	}
+
 	return command.Run(ctx, "goimports", args...)
 }
 

internal/librarian/golang/format_test.go

@@ -107,7 +107,7 @@ func main() {
 					t.Fatal(err)
 				}
 			}
-			if err := Format(t.Context(), test.library); err != nil {
+			if err := Format(t.Context(), test.library, nil); err != nil {
 				t.Fatal(err)
 			}
 			for _, aPath := range test.goFilePath {

internal/librarian/golang/install.go

@@ -16,22 +16,48 @@ package golang
 
 import (
 	"context"
+	_ "embed"
+	"errors"
+	"fmt"
 
 	"github.com/googleapis/librarian/internal/command"
+	"github.com/googleapis/librarian/internal/config"
+	"github.com/googleapis/librarian/internal/yaml"
 )
 
-var tools = []string{
-	"github.com/googleapis/gapic-generator-go/cmd/protoc-gen-go_gapic@v0.58.0",
-	"golang.org/x/tools/cmd/goimports@latest",
-	"google.golang.org/grpc/cmd/protoc-gen-go-grpc@v1.3.0",
-	"google.golang.org/protobuf/cmd/protoc-gen-go@v1.36.11",
-}
+//go:embed librarian.yaml
+var librarianYAML []byte
+
+// ErrMissingToolVersion indicates a go tool entry is missing its version.
+var ErrMissingToolVersion = errors.New("go tool missing version")
 
 // Install installs the tools required for Go library generation.
-func Install(ctx context.Context) error {
-	for _, tool := range tools {
-		if err := command.Run(ctx, command.Go, "install", tool); err != nil {
-			return err
+func Install(ctx context.Context, tools *config.Tools) error {
+	if tools == nil || len(tools.Go) == 0 {
+		return installFallbackTools(ctx)
+	}
+	return installGoTools(ctx, tools.Go)
+}
+
+func installFallbackTools(ctx context.Context) error {
+	cfg, err := yaml.Unmarshal[config.Config](librarianYAML)
+	if err != nil {
+		return fmt.Errorf("parsing embedded librarian.yaml: %w", err)
+	}
+	if cfg.Tools == nil || len(cfg.Tools.Go) == 0 {
+		return fmt.Errorf("no go tools defined in embedded librarian.yaml")
+	}
+	return installGoTools(ctx, cfg.Tools.Go)
+}
+
+func installGoTools(ctx context.Context, goTools []*config.GoTool) error {
+	for _, tool := range goTools {
+		if tool.Version == "" {
+			return fmt.Errorf("%w: %s", ErrMissingToolVersion, tool.Name)
+		}
+		toolStr := fmt.Sprintf("%s@%s", tool.Name, tool.Version)
+		if err := command.Run(ctx, command.Go, "install", toolStr); err != nil {
+			return fmt.Errorf("install %s: %w", toolStr, err)
 		}
 	}
 	return nil

internal/librarian/golang/install_test.go

@@ -24,7 +24,7 @@ import (
 func TestInstall(t *testing.T) {
 	gobin := t.TempDir()
 	t.Setenv("GOBIN", gobin)
-	if err := Install(t.Context()); err != nil {
+	if err := Install(t.Context(), nil); err != nil {
 		t.Fatal(err)
 	}
 	suffix := ""

internal/librarian/golang/librarian.yaml

@@ -0,0 +1,28 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# TODO(https://github.com/googleapis/librarian/issues/5449): move this file to
+# github.com/googleapis/google-cloud-go after the repository has migrated to
+# librarian.
+language: go
+tools:
+  go:
+    - name: github.com/googleapis/gapic-generator-go/cmd/protoc-gen-go_gapic
+      version: v0.58.0
+    - name: golang.org/x/tools/cmd/goimports
+      version: v0.44.0
+    - name: google.golang.org/grpc/cmd/protoc-gen-go-grpc
+      version: v1.3.0
+    - name: google.golang.org/protobuf/cmd/protoc-gen-go
+      version: v1.36.11

internal/librarian/librarian.go

@@ -83,17 +83,22 @@ from librarian.yaml in the current directory.`,
 			if lang == "" {
 				lang = cfg.Language
 			}
+			var tools *config.Tools
+			if cfg != nil {
+				tools = cfg.Tools
+			}
+
 			switch lang {
 			case config.LanguageFake:
 				return nil
 			case config.LanguageGo:
-				return golang.Install(ctx)
+				return golang.Install(ctx, tools)
 			case config.LanguageNodejs:
 				return nodejs.Install(ctx)
 			case config.LanguagePython:
 				return python.Install(ctx)
 			case config.LanguageRust:
-				return rust.Install(ctx, cfg.Tools)
+				return rust.Install(ctx, tools)
 			default:
 				return fmt.Errorf("language %q does not support install", lang)
 			}