feat(internal/serviceconfig): add Find to add default paths (#3096)

FindServiceConfig locates the service config file for an API path by
scanning for YAML files containing `type: google.api.Service` in the
first 5 lines, while skipping `_gapic.yaml` files.

The generate command now automatically populates the ServiceConfig field
for APIs that don't have one explicitly configured. This reduces manual
configuration when adding new libraries, when we can determine the
service config path from the API path.

Author: julieqiu

internal/config/config.go

@@ -60,7 +60,7 @@ type Source struct {
 
 	// Dir is a local directory path to use instead of fetching.
 	// If set, Commit and SHA256 are ignored.
-	Dir string `yaml:"-"`
+	Dir string `yaml:"dir,omitempty"`
 }
 
 // Default contains default settings for all libraries.

internal/librarian/generate.go

@@ -20,11 +20,15 @@ import (
 	"fmt"
 
 	"github.com/googleapis/librarian/internal/config"
+	"github.com/googleapis/librarian/internal/fetch"
 	"github.com/googleapis/librarian/internal/librarian/internal/rust"
+	"github.com/googleapis/librarian/internal/serviceconfig"
 	"github.com/googleapis/librarian/internal/yaml"
 	"github.com/urfave/cli/v3"
 )
 
+const googleapisRepo = "github.com/googleapis/googleapis"
+
 var (
 	errMissingLibraryOrAllFlag = errors.New("must specify library name or use --all flag")
 	errBothLibraryAndAllFlag   = errors.New("cannot specify both library name and --all flag")
@@ -71,21 +75,30 @@ func runGenerate(ctx context.Context, all bool, libraryName string) error {
 }
 
 func generateAll(ctx context.Context, cfg *config.Config) error {
-	var errs []error
 	for _, lib := range cfg.Libraries {
-		if err := generate(ctx, cfg.Language, lib, cfg.Sources); err != nil {
-			errs = append(errs, err)
+		if err := generateLibrary(ctx, cfg, lib.Name); err != nil {
+			return err
 		}
 	}
-	if len(errs) > 0 {
-		return errors.Join(errs...)
-	}
 	return nil
 }
 
 func generateLibrary(ctx context.Context, cfg *config.Config, libraryName string) error {
+	googleapisDir, err := fetchGoogleapisDir(ctx, cfg.Sources)
+	if err != nil {
+		return err
+	}
 	for _, lib := range cfg.Libraries {
 		if lib.Name == libraryName {
+			for _, api := range lib.Channels {
+				if api.ServiceConfig == "" {
+					serviceConfig, err := serviceconfig.Find(googleapisDir, api.Path)
+					if err != nil {
+						return err
+					}
+					api.ServiceConfig = serviceConfig
+				}
+			}
 			return generate(ctx, cfg.Language, lib, cfg.Sources)
 		}
 	}
@@ -102,11 +115,20 @@ func generate(ctx context.Context, language string, library *config.Library, sou
 	default:
 		err = fmt.Errorf("generate not implemented for %q", language)
 	}
-
 	if err != nil {
 		fmt.Printf("✗ Error generating %s: %v\n", library.Name, err)
 		return err
 	}
 	fmt.Printf("✓ Successfully generated %s\n", library.Name)
 	return nil
 }
+
+func fetchGoogleapisDir(ctx context.Context, sources *config.Sources) (string, error) {
+	if sources == nil || sources.Googleapis == nil {
+		return "", errors.New("googleapis source is required")
+	}
+	if sources.Googleapis.Dir != "" {
+		return sources.Googleapis.Dir, nil
+	}
+	return fetch.RepoDir(ctx, googleapisRepo, sources.Googleapis.Commit, sources.Googleapis.SHA256)
+}

internal/librarian/generate_test.go

@@ -31,19 +31,31 @@ func TestGenerateCommand(t *testing.T) {
 		lib2       = "library-two"
 		lib2Output = "output2"
 	)
+	wd, err := os.Getwd()
+	if err != nil {
+		t.Fatal(err)
+	}
+	googleapisDir := filepath.Join(wd, "testdata", "googleapis")
+
 	tempDir := t.TempDir()
 	t.Chdir(tempDir)
 	configPath := filepath.Join(tempDir, librarianConfigPath)
+
 	configContent := fmt.Sprintf(`language: testhelper
 sources:
   googleapis:
-    commit: abc123
+    dir: %s
 libraries:
   - name: %s
     output: %s
+    apis:
+      - path: google/cloud/speech/v1
+      - path: google/cloud/speech/v1p1beta1
+      - path: google/cloud/speech/v2
+      - path: grafeas/v1
   - name: %s
     output: %s
-`, lib1, lib1Output, lib2, lib2Output)
+`, googleapisDir, lib1, lib1Output, lib2, lib2Output)
 	if err := os.WriteFile(configPath, []byte(configContent), 0644); err != nil {
 		t.Fatal(err)
 	}

internal/serviceconfig/serviceconfig.go

@@ -16,9 +16,12 @@
 package serviceconfig
 
 import (
+	"bufio"
 	"encoding/json"
 	"fmt"
 	"os"
+	"path/filepath"
+	"strings"
 
 	"github.com/googleapis/librarian/internal/yaml"
 	"google.golang.org/genproto/googleapis/api/serviceconfig"
@@ -67,3 +70,57 @@ func Read(serviceConfigPath string) (*Service, error) {
 	}
 	return cfg, nil
 }
+
+// Find finds the service config file for a channel path. It looks for YAML
+// files containing "type: google.api.Service", skipping any files ending in
+// _gapic.yaml.
+//
+// The apiPath should be relative to googleapisDir (e.g.,
+// "google/cloud/secretmanager/v1"). Returns the service config path relative
+// to googleapisDir, or empty string if not found.
+func Find(googleapisDir, apiPath string) (string, error) {
+	dir := filepath.Join(googleapisDir, apiPath)
+	entries, err := os.ReadDir(dir)
+	if err != nil {
+		return "", err
+	}
+	for _, entry := range entries {
+		if entry.IsDir() {
+			continue
+		}
+		name := entry.Name()
+		if !strings.HasSuffix(name, ".yaml") {
+			continue
+		}
+		if strings.HasSuffix(name, "_gapic.yaml") {
+			continue
+		}
+
+		path := filepath.Join(dir, name)
+		isServiceConfig, err := isServiceConfigFile(path)
+		if err != nil {
+			return "", err
+		}
+		if isServiceConfig {
+			return filepath.Join(apiPath, name), nil
+		}
+	}
+	return "", nil
+}
+
+// isServiceConfigFile checks if the file contains "type: google.api.Service".
+func isServiceConfigFile(path string) (bool, error) {
+	f, err := os.Open(path)
+	if err != nil {
+		return false, err
+	}
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for i := 0; i < 20 && scanner.Scan(); i++ {
+		if strings.TrimSpace(scanner.Text()) == "type: google.api.Service" {
+			return true, nil
+		}
+	}
+	return false, scanner.Err()
+}

internal/serviceconfig/serviceconfig_test.go

@@ -77,3 +77,14 @@ func TestNoGenprotoServiceConfigImports(t *testing.T) {
 			len(violations), genprotoImport, strings.Join(violations, "\n  "))
 	}
 }
+
+func TestFind(t *testing.T) {
+	got, err := Find("testdata/googleapis", "google/cloud/speech/v1")
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := "google/cloud/speech/v1/speech_v1.yaml"
+	if got != want {
+		t.Errorf("got %q, want %q", got, want)
+	}
+}

internal/serviceconfig/testdata/googleapis/google/cloud/speech/v1/speech_v1.yaml

@@ -0,0 +1,58 @@
+# Copyright 2025 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.
+type: google.api.Service
+config_version: 3
+name: speech.googleapis.com
+title: Cloud Speech-to-Text API
+apis:
+  - name: google.cloud.speech.v1.Adaptation
+  - name: google.cloud.speech.v1.Speech
+  - name: google.longrunning.Operations
+types:
+  - name: google.cloud.speech.v1.LongRunningRecognizeMetadata
+  - name: google.cloud.speech.v1.LongRunningRecognizeResponse
+documentation:
+  summary: Converts audio to text by applying powerful neural network models.
+  overview: |-
+    # Introduction
+
+    Google Cloud Speech API provides speech recognition as a service.
+backend:
+  rules:
+    - selector: 'google.cloud.speech.v1.Adaptation.*'
+      deadline: 355.0
+    - selector: 'google.cloud.speech.v1.Speech.*'
+      deadline: 355.0
+    - selector: 'google.longrunning.Operations.*'
+      deadline: 355.0
+http:
+  rules:
+    - selector: google.longrunning.Operations.GetOperation
+      get: '/v1/operations/{name=**}'
+    - selector: google.longrunning.Operations.ListOperations
+      get: /v1/operations
+authentication:
+  rules:
+    - selector: 'google.cloud.speech.v1.Adaptation.*'
+      oauth:
+        canonical_scopes: |-
+          https://www.googleapis.com/auth/cloud-platform
+    - selector: 'google.cloud.speech.v1.Speech.*'
+      oauth:
+        canonical_scopes: |-
+          https://www.googleapis.com/auth/cloud-platform
+    - selector: 'google.longrunning.Operations.*'
+      oauth:
+        canonical_scopes: |-
+          https://www.googleapis.com/auth/cloud-platform