feat(internal/sideflip/config): add initial config (#2965)

Add structs for librarian.yaml with read/write support, including
support for migrating sidekick.toml data to new Rust types.

For #2966

Author: julieqiu

internal/sideflip/config/config.go

@@ -0,0 +1,215 @@
+// 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
+//
+//     http://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.
+
+package config
+
+import (
+	"fmt"
+	"os"
+
+	"gopkg.in/yaml.v3"
+)
+
+// Config represents the complete librarian.yaml configuration file.
+type Config struct {
+	// Version is the version of librarian that created this config.
+	Version string `yaml:"version"`
+
+	// Language is the primary language for this repository (go, python, rust).
+	Language string `yaml:"language"`
+
+	// Repo is the repository name (e.g., "googleapis/google-cloud-python").
+	Repo string `yaml:"repo,omitempty"`
+
+	// Sources contains references to external source repositories.
+	Sources *Sources `yaml:"sources,omitempty"`
+
+	// Default contains default generation settings.
+	Default *Default `yaml:"default"`
+
+	// Libraries contains configuration overrides for libraries that need special handling.
+	// Only include libraries that differ from defaults.
+	// Versions are looked up from the Versions map below.
+	Libraries []*Library `yaml:"libraries,omitempty"`
+
+	// Versions contains version numbers for all libraries.
+	// This is the source of truth for release versions.
+	// Key is library name, value is version string.
+	Versions map[string]string `yaml:"versions,omitempty"`
+}
+
+// Sources contains references to external source repositories.
+// Each entry maps a source name to its configuration.
+type Sources struct {
+	// Discovery is the discovery-artifact-manager repository configuration.
+	Discovery *Source `yaml:"discovery,omitempty"`
+
+	// Googleapis is the googleapis repository configuration.
+	Googleapis *Source `yaml:"googleapis,omitempty"`
+}
+
+// Source represents a single source repository configuration.
+type Source struct {
+	// Commit is the git commit hash or tag to use.
+	Commit string `yaml:"commit"`
+}
+
+// Default contains default generation settings.
+type Default struct {
+	// Output is the directory where generated code is written (relative to repository root).
+	Output string `yaml:"output,omitempty"`
+
+	// Generate contains default generation configuration.
+	Generate *DefaultGenerate `yaml:"generate,omitempty"`
+
+	// Release contains default release configuration.
+	Release *DefaultRelease `yaml:"release,omitempty"`
+
+	// Rust contains Rust-specific default configuration.
+	Rust *RustDefault `yaml:"rust,omitempty"`
+}
+
+// DefaultGenerate contains default generation configuration.
+type DefaultGenerate struct {
+	// Auto generates all client libraries with default configurations
+	// for the language, unless otherwise specified.
+	Auto bool `yaml:"auto,omitempty"`
+
+	// OneLibraryPer specifies packaging strategy: "api" or "channel".
+	// - "api": Bundle all versions of a service into one library (Python, Go default)
+	// - "channel": Create separate library per version (Rust, Dart default)
+	OneLibraryPer string `yaml:"one_library_per,omitempty"`
+
+	// Transport is the default transport protocol (e.g., "grpc+rest", "grpc").
+	Transport string `yaml:"transport,omitempty"`
+
+	// ReleaseLevel is the default release level ("stable" or "preview").
+	ReleaseLevel string `yaml:"release_level,omitempty"`
+}
+
+// DefaultRelease contains release configuration.
+type DefaultRelease struct {
+	// TagFormat is the template for git tags (e.g., '{name}/v{version}').
+	// Supported placeholders: {name}, {version}
+	TagFormat string `yaml:"tag_format,omitempty"`
+
+	// Remote is the git remote name (e.g., "upstream", "origin").
+	Remote string `yaml:"remote,omitempty"`
+
+	// Branch is the default branch for releases (e.g., "main", "master").
+	Branch string `yaml:"branch,omitempty"`
+}
+
+// Library represents a single library configuration entry.
+type Library struct {
+	// APIServiceConfigs maps API paths to their service config file paths (runtime only, not serialized).
+	// For single-API libraries: map[API]serviceConfigPath
+	// For multi-API libraries: map[APIs[0]]path1, map[APIs[1]]path2, etc.
+	APIServiceConfigs map[string]string `yaml:"-"`
+
+	// Channel specifies which googleapis Channel to generate from (for generated libraries).
+	// Can be a string (protobuf Channel path) or an APIObject (for discovery APIs).
+	// If both Channel and APIs are empty, this is a handwritten library.
+	Channel string `yaml:"channel,omitempty"`
+
+	// 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"`
+
+	// CopyrightYear is the copyright year for the library.
+	CopyrightYear string `yaml:"copyright_year,omitempty"`
+
+	// Generate contains per-library generate configuration.
+	Generate *LibraryGenerate `yaml:"generate,omitempty"`
+
+	// Keep lists files/directories to preserve during regeneration.
+	Keep []string `yaml:"keep,omitempty"`
+
+	// Name is the library name (e.g., "secretmanager", "storage").
+	Name string `yaml:"name,omitempty"`
+
+	// Output specifies the filesystem location (overrides computed location from defaults.output).
+	// For generated libraries: overrides where code is generated to.
+	// For handwritten libraries: specifies the source directory.
+	Output string `yaml:"output,omitempty"`
+
+	// Publish contains per-library publish configuration.
+	Publish *LibraryPublish `yaml:"publish,omitempty"`
+
+	// Release contains per-library release configuration.
+	Release *LibraryRelease `yaml:"release,omitempty"`
+
+	// ReleaseLevel overrides the default release level.
+	ReleaseLevel string `yaml:"release_level,omitempty"`
+
+	// Rust contains Rust-specific library configuration.
+	Rust *RustCrate `yaml:"rust,omitempty"`
+
+	// Transport overrides the default transport.
+	Transport string `yaml:"transport,omitempty"`
+
+	// Version is the library version.
+	Version string `yaml:"version,omitempty"`
+}
+
+// LibraryGenerate contains per-library generate configuration.
+type LibraryGenerate struct {
+	// Disabled prevents library generation.
+	Disabled bool `yaml:"disabled,omitempty"`
+}
+
+// LibraryRelease contains per-library release configuration.
+type LibraryRelease struct {
+	// Disabled prevents library release.
+	Disabled bool `yaml:"disabled,omitempty"`
+}
+
+// LibraryPublish contains per-library publish configuration.
+type LibraryPublish struct {
+	// Disabled prevents library from being published to package registries.
+	Disabled bool `yaml:"disabled,omitempty"`
+}
+
+// Read reads the configuration from a file.
+func Read(path string) (*Config, error) {
+	data, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("failed to read config file: %w", err)
+	}
+
+	var c Config
+	if err := yaml.Unmarshal(data, &c); err != nil {
+		return nil, fmt.Errorf("failed to unmarshal config: %w", err)
+	}
+	return &c, nil
+}
+
+// Write writes the configuration to a file.
+func (c *Config) Write(path string) error {
+	f, err := os.OpenFile(path, os.O_CREATE|os.O_WRONLY|os.O_TRUNC, 0644)
+	if err != nil {
+		return fmt.Errorf("failed to open config file: %w", err)
+	}
+	defer f.Close()
+
+	enc := yaml.NewEncoder(f)
+	enc.SetIndent(2)
+	defer enc.Close()
+
+	if err := enc.Encode(c); err != nil {
+		return fmt.Errorf("failed to marshal config: %w", err)
+	}
+
+	return nil
+}

internal/sideflip/config/config_test.go

@@ -0,0 +1,49 @@
+// 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
+//
+//     http://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.
+
+package config
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"gopkg.in/yaml.v3"
+)
+
+func TestReadWrite(t *testing.T) {
+	cfg, err := Read("testdata/rust/librarian.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var got bytes.Buffer
+	enc := yaml.NewEncoder(&got)
+	enc.SetIndent(2)
+	if err := enc.Encode(cfg); err != nil {
+		t.Fatal(err)
+	}
+
+	wantCfg, err := Read("testdata/rust/librarian.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	var gotCfg Config
+	if err := yaml.Unmarshal(got.Bytes(), &gotCfg); err != nil {
+		t.Fatal(err)
+	}
+
+	if diff := cmp.Diff(wantCfg, &gotCfg); diff != "" {
+		t.Errorf("mismatch (-want +got):\n%s", diff)
+	}
+}