refactor(internal/config): create Channel struct (#3081)

The Channel, ServiceConfig, SpecificationFormat fields have been moved
from config.Library to a new config.Channel struct. This refactors the
configuration to better support cases when there are multiple channels
within a single library.

Author: julieqiu

internal/config/config.go

@@ -119,7 +119,7 @@ type Library struct {
 
 	// Channels specifies multiple API versions to bundle into one library (for multi-version libraries).
 	// Alternative to API field for libraries that bundle multiple versions.
-	Channels []string `yaml:"channels,omitempty"`
+	Channels []*Channel `yaml:"channels,omitempty"`
 
 	// CopyrightYear is the copyright year for the library.
 	CopyrightYear string `yaml:"copyright_year,omitempty"`
@@ -147,20 +147,27 @@ type Library struct {
 	// Rust contains Rust-specific library configuration.
 	Rust *RustCrate `yaml:"rust,omitempty"`
 
-	// SpecificationFormat specifies the API specification format.
-	// Valid values are "protobuf" (default) or "discovery".
+	// SpecificationFormat specifies the API specification format. Valid values
+	// are "protobuf" (default) or "discovery".
 	SpecificationFormat string `yaml:"specification_format,omitempty"`
 
-	// ServiceConfig is the path to the service config file.
-	ServiceConfig string `yaml:"-"`
-
 	// Transport overrides the default transport.
 	Transport string `yaml:"transport,omitempty"`
 
 	// Version is the library version.
 	Version string `yaml:"version,omitempty"`
 }
 
+// Channel contains information about an API channel.
+type Channel struct {
+	// Path specifies which googleapis Path to generate from (for generated
+	// libraries).
+	Path string `yaml:"channel,omitempty"`
+
+	// ServiceConfig is the path to the service config file.
+	ServiceConfig string `yaml:"service_config,omitempty"`
+}
+
 // LibraryGenerate contains per-library generate configuration.
 type LibraryGenerate struct {
 	// Disabled prevents library generation.

internal/config/testdata/rust/librarian.yaml

@@ -38,9 +38,11 @@ default:
         force_used: true
 libraries:
   - name: google-cloud-secretmanager-v1
-    channel: google/cloud/secretmanager/v1
+    channels:
+      - path: google/cloud/secretmanager/v1
   - name: google-cloud-storage-v2
-    channel: google/cloud/storage/v2
+    channels:
+      - path: google/cloud/storage/v2
     rust:
       disabled_rustdoc_warnings:
         - rustdoc::bare_urls

internal/language/internal/rust/codec.go

@@ -21,7 +21,7 @@ import (
 	sidekickconfig "github.com/googleapis/librarian/internal/sidekick/config"
 )
 
-func toSidekickConfig(library *config.Library, serviceConfig, googleapisDir, discoveryDir string) *sidekickconfig.Config {
+func toSidekickConfig(library *config.Library, channel *config.Channel, googleapisDir, discoveryDir string) *sidekickconfig.Config {
 	source := map[string]string{
 		"googleapis-root": googleapisDir,
 	}
@@ -35,8 +35,8 @@ func toSidekickConfig(library *config.Library, serviceConfig, googleapisDir, dis
 		General: sidekickconfig.GeneralConfig{
 			Language:            "rust",
 			SpecificationFormat: specFormat,
-			ServiceConfig:       serviceConfig,
-			SpecificationSource: library.Channel,
+			ServiceConfig:       channel.ServiceConfig,
+			SpecificationSource: channel.Path,
 		},
 		Source: source,
 		Codec:  buildCodec(library),

internal/language/internal/rust/codec_test.go

@@ -26,19 +26,21 @@ func TestToSidekickConfig(t *testing.T) {
 	for _, test := range []struct {
 		name          string
 		library       *config.Library
-		serviceConfig string
+		channel       *config.Channel
 		googleapisDir string
 		discoveryDir  string
 		want          *sidekickconfig.Config
 	}{
 		{
 			name: "minimal config",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
+			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -57,13 +59,15 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with version and release level",
 			library: &config.Library{
-				Channel:      "google/cloud/storage/v1",
 				Name:         "google-cloud-storage",
 				Version:      "0.1.0",
 				ReleaseLevel: "preview",
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -84,12 +88,14 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with copyright year",
 			library: &config.Library{
-				Channel:       "google/cloud/storage/v1",
 				Name:          "google-cloud-storage",
 				CopyrightYear: "2024",
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -109,8 +115,7 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with rust config",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
 				Rust: &config.RustCrate{
 					ModulePath:                "gcs",
 					PerServiceFeatures:        true,
@@ -126,8 +131,11 @@ func TestToSidekickConfig(t *testing.T) {
 					TemplateOverride:          "custom-template",
 				},
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -158,15 +166,17 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with publish disabled",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
 				Publish: &config.LibraryPublish{
 					Disabled: true,
 				},
 				Rust: &config.RustCrate{},
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -186,8 +196,7 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with package dependencies",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
 				Rust: &config.RustCrate{
 					PackageDependencies: []config.RustPackageDependency{
 						{
@@ -201,8 +210,11 @@ func TestToSidekickConfig(t *testing.T) {
 					},
 				},
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -222,8 +234,7 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with documentation overrides",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
 				Rust: &config.RustCrate{
 					DocumentationOverrides: []config.RustDocumentationOverride{
 						{
@@ -234,8 +245,11 @@ func TestToSidekickConfig(t *testing.T) {
 					},
 				},
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -261,8 +275,7 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with pagination overrides",
 			library: &config.Library{
-				Channel: "google/cloud/storage/v1",
-				Name:    "google-cloud-storage",
+				Name: "google-cloud-storage",
 				Rust: &config.RustCrate{
 					PaginationOverrides: []config.RustPaginationOverride{
 						{
@@ -272,8 +285,11 @@ func TestToSidekickConfig(t *testing.T) {
 					},
 				},
 			},
+			channel: &config.Channel{
+				Path:          "google/cloud/storage/v1",
+				ServiceConfig: "google/cloud/storage/v1/storage_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
-			serviceConfig: "google/cloud/storage/v1/storage_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -298,13 +314,15 @@ func TestToSidekickConfig(t *testing.T) {
 		{
 			name: "with discovery format",
 			library: &config.Library{
-				Channel:             "discoveries/compute.v1.json",
 				Name:                "google-cloud-compute-v1",
 				SpecificationFormat: "discovery",
 			},
+			channel: &config.Channel{
+				Path:          "discoveries/compute.v1.json",
+				ServiceConfig: "google/cloud/compute/v1/compute_v1.yaml",
+			},
 			googleapisDir: "/tmp/googleapis",
 			discoveryDir:  "/tmp/discovery-artifact-manager",
-			serviceConfig: "google/cloud/compute/v1/compute_v1.yaml",
 			want: &sidekickconfig.Config{
 				General: sidekickconfig.GeneralConfig{
 					Language:            "rust",
@@ -324,7 +342,7 @@ func TestToSidekickConfig(t *testing.T) {
 		},
 	} {
 		t.Run(test.name, func(t *testing.T) {
-			got := toSidekickConfig(test.library, test.serviceConfig, test.googleapisDir, test.discoveryDir)
+			got := toSidekickConfig(test.library, test.channel, test.googleapisDir, test.discoveryDir)
 			if diff := cmp.Diff(test.want, got); diff != "" {
 				t.Errorf("mismatch (-want +got):\n%s", diff)
 			}

internal/language/internal/rust/generate.go

@@ -16,6 +16,7 @@ package rust
 
 import (
 	"context"
+	"fmt"
 
 	"github.com/googleapis/librarian/internal/config"
 	"github.com/googleapis/librarian/internal/fetch"
@@ -38,7 +39,10 @@ func Generate(ctx context.Context, library *config.Library, sources *config.Sour
 	if err != nil {
 		return err
 	}
-	sidekickConfig := toSidekickConfig(library, library.ServiceConfig, googleapisDir, discoveryDir)
+	if len(library.Channels) != 1 {
+		return fmt.Errorf("the Rust generator only supports a single channel per library")
+	}
+	sidekickConfig := toSidekickConfig(library, library.Channels[0], googleapisDir, discoveryDir)
 	model, err := parser.CreateModel(sidekickConfig)
 	if err != nil {
 		return err

internal/language/internal/rust/generate_test.go

@@ -34,10 +34,14 @@ func TestGenerate(t *testing.T) {
 	outDir := t.TempDir()
 	googleapisDir := filepath.Join(testdataDir, "googleapis")
 	library := &config.Library{
-		Name:          "secretmanager",
-		Output:        outDir,
-		ServiceConfig: "google/cloud/secretmanager/v1/secretmanager_v1.yaml",
-		Channel:       "google/cloud/secretmanager/v1",
+		Name:   "secretmanager",
+		Output: outDir,
+		Channels: []*config.Channel{
+			{
+				Path:          "google/cloud/secretmanager/v1",
+				ServiceConfig: "google/cloud/secretmanager/v1/secretmanager_v1.yaml",
+			},
+		},
 		Version:       "0.1.0",
 		ReleaseLevel:  "preview",
 		CopyrightYear: "2025",