librarian: add publish command and supporting config (#3262)

This change is part 1 of changes to port over `rust-publish` for Rust. 

- setup skeleton of `librarian publish` command
- copy Rust [release related
config](https://github.com/googleapis/librarian/blob/main/internal/sidekick/config/release.go)
into a new Release struct in config. This is to allow seamless migrate
`rust-publish` to librarian for now, may be refactored later.



For #3153

Author: zhumin8

internal/config/config.go

@@ -33,6 +33,52 @@ type Config struct {
 	// Libraries contains configuration overrides for libraries that need
 	// special handling, and differ from default settings.
 	Libraries []*Library `yaml:"libraries,omitempty"`
+
+	// Release holds the configuration parameter for any `${lang}-release` subcommand.
+	Release *Release `yaml:"release,omitempty"`
+}
+
+// Release holds the configuration parameter for publish command.
+type Release struct {
+	// Remote sets the name of the source-of-truth remote for releases, typically `upstream`.
+	Remote string `yaml:"remote,omitempty"`
+
+	// Branch sets the name of the release branch, typically `main`
+	Branch string `yaml:"branch,omitempty"`
+
+	// Tools defines the list of tools to install, indexed by installer.
+	Tools map[string][]Tool `yaml:"tools,omitempty"`
+
+	// Preinstalled tools defines the list of tools that must be pre-installed.
+	//
+	// This is indexed by the well-known name of the tool vs. its path, e.g.
+	// [preinstalled]
+	// cargo = /usr/bin/cargo
+	Preinstalled map[string]string `yaml:"preinstalled,omitempty"`
+
+	// IgnoredChanges defines globs that are ignored in change analysis.
+	IgnoredChanges []string `yaml:"ignored_changes,omitempty"`
+
+	// An alternative location for the `roots.pem` file. If empty it has no
+	// effect.
+	RootsPem string `yaml:"roots_pem,omitempty"`
+}
+
+// GetExecutablePath finds the path for a given command, checking for an
+// override in the configuration first.
+func (r *Release) GetExecutablePath(commandName string) string {
+	if r != nil && r.Preinstalled != nil {
+		if exe, ok := r.Preinstalled[commandName]; ok {
+			return exe
+		}
+	}
+	return commandName
+}
+
+// Tool defines the configuration required to install helper tools.
+type Tool struct {
+	Name    string `yaml:"name"`
+	Version string `yaml:"version,omitempty"`
 }
 
 // Sources references external source repositories.

internal/config/config_test.go

@@ -137,3 +137,54 @@ func TestWrite(t *testing.T) {
 		t.Errorf("mismatch (-want +got):\n%s", diff)
 	}
 }
+
+func TestReleaseGetExecutablePath(t *testing.T) {
+	tests := []struct {
+		name           string
+		releaseConfig  *Release
+		executableName string
+		want           string
+	}{
+		{
+			name: "Preinstalled tool found",
+			releaseConfig: &Release{
+				Preinstalled: map[string]string{
+					"cargo": "/usr/bin/cargo",
+					"git":   "/usr/bin/git",
+				},
+			},
+			executableName: "cargo",
+			want:           "/usr/bin/cargo",
+		},
+		{
+			name: "Preinstalled tool not found",
+			releaseConfig: &Release{
+				Preinstalled: map[string]string{
+					"git": "/usr/bin/git",
+				},
+			},
+			executableName: "cargo",
+			want:           "cargo",
+		},
+		{
+			name:           "No preinstalled section",
+			releaseConfig:  &Release{},
+			executableName: "cargo",
+			want:           "cargo",
+		},
+		{
+			name:           "Nil release config",
+			releaseConfig:  nil,
+			executableName: "cargo",
+			want:           "cargo",
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := test.releaseConfig.GetExecutablePath(test.executableName)
+			if diff := cmp.Diff(test.want, got); diff != "" {
+				t.Errorf("GetExecutablePath() mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}

internal/librarian/librarian.go

@@ -39,6 +39,7 @@ func Run(ctx context.Context, args ...string) error {
 			tidyCommand(),
 			updateCommand(),
 			versionCommand(),
+			publishCommand(),
 		},
 	}
 	return cmd.Run(ctx, args)

internal/librarian/publish.go

@@ -0,0 +1,57 @@
+// 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.
+
+package librarian
+
+import (
+	"context"
+	"fmt"
+
+	"github.com/googleapis/librarian/internal/config"
+	"github.com/googleapis/librarian/internal/yaml"
+	"github.com/urfave/cli/v3"
+)
+
+func publishCommand() *cli.Command {
+	return &cli.Command{
+		Name:      "publish",
+		Usage:     "publishes client libraries",
+		UsageText: "librarian publish",
+		Flags: []cli.Flag{
+			&cli.BoolFlag{
+				Name:  "dry-run",
+				Usage: "print commands without executing",
+			},
+			&cli.BoolFlag{
+				Name:  "skip-semver-checks",
+				Usage: "skip semantic versioning checks",
+			},
+		},
+		Action: func(ctx context.Context, cmd *cli.Command) error {
+			cfg, err := yaml.Read[config.Config](librarianConfigPath)
+			if err != nil {
+				return err
+			}
+			dryRun := cmd.Bool("dry-run")
+			skipSemverChecks := cmd.Bool("skip-semver-checks")
+			return publish(ctx, cfg, dryRun, skipSemverChecks)
+		},
+	}
+}
+
+func publish(ctx context.Context, cfg *config.Config, dryRun bool, skipSemverChecks bool) error {
+	// TODO: Not yet implemented.
+	fmt.Printf("publish not implemented. ctx: %v, cfg: %v, dryRun: %v, skipSemverChecks: %v\n", ctx, cfg, dryRun, skipSemverChecks)
+	panic("not implemented")
+}