feat: get library changes in release init command (#1780)

Updates #1008

Author: JoeWang1127

internal/config/state.go

@@ -94,6 +94,9 @@ type LibraryState struct {
 	Version string `yaml:"version" json:"version"`
 	// The commit hash from the API definition repository at which the library was last generated.
 	LastGeneratedCommit string `yaml:"last_generated_commit" json:"last_generated_commit"`
+	// The changes from the language repository since the library was last released.
+	// This field is ignored when writing to state.yaml.
+	Changes []*Change `yaml:"-" json:"changes,omitempty"`
 	// A list of APIs that are part of this library.
 	APIs []*API `yaml:"apis" json:"apis"`
 	// A list of directories in the language repository where Librarian contributes code.
@@ -213,6 +216,20 @@ func (a *API) Validate() error {
 	return nil
 }
 
+// Change represents the changelog of a library.
+type Change struct {
+	// The type of the change, should be one of the conventional type.
+	Type string `yaml:"type" json:"type"`
+	// The summary of the change.
+	Subject string `yaml:"subject" json:"subject"`
+	// The body of the change.
+	Body string `yaml:"body" json:"body"`
+	// The Changelist number in piper associated with this change.
+	ClNum string `yaml:"piper_cl_number" json:"piper_cl_number"`
+	// The commit hash in the source repository associated with this change.
+	CommitHash string `yaml:"source_commit_hash" json:"source_commit_hash"`
+}
+
 // invalidPathChars contains characters that are invalid in path components,
 // plus path separators and the null byte.
 const invalidPathChars = "<>:\"|?*/\\\x00"

internal/librarian/init_test.go

@@ -15,12 +15,17 @@
 package librarian
 
 import (
+	"fmt"
 	"log"
+	"math/rand"
 	"os"
 	"os/exec"
 	"path/filepath"
 	"testing"
 
+	"github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/plumbing/object"
+
 	"github.com/googleapis/librarian/internal/config"
 	"github.com/googleapis/librarian/internal/gitrepo"
 	"gopkg.in/yaml.v3"
@@ -169,3 +174,68 @@ func runGit(t *testing.T, dir string, args ...string) {
 		t.Fatalf("git %v: %v", args, err)
 	}
 }
+
+// setupRepoForGetCommits creates an empty gitrepo and creates some commits and
+// tags.
+//
+// Each commit has a file path and a commit message.
+// Note that pathAndMessages should at least have one element. All tags are created
+// after the first commit.
+func setupRepoForGetCommits(t *testing.T, pathAndMessages []pathAndMessage, tags []string) *gitrepo.LocalRepository {
+	t.Helper()
+	dir := t.TempDir()
+	gitRepo, err := git.PlainInit(dir, false)
+	if err != nil {
+		t.Fatalf("git.PlainInit failed: %v", err)
+	}
+
+	createAndCommit := func(path, msg string) {
+		w, err := gitRepo.Worktree()
+		if err != nil {
+			t.Fatalf("Worktree() failed: %v", err)
+		}
+		fullPath := filepath.Join(dir, path)
+		if err := os.MkdirAll(filepath.Dir(fullPath), 0755); err != nil {
+			t.Fatalf("os.MkdirAll failed: %v", err)
+		}
+		content := fmt.Sprintf("content-%d", rand.Intn(10000))
+		if err := os.WriteFile(fullPath, []byte(content), 0644); err != nil {
+			t.Fatalf("os.WriteFile failed: %v", err)
+		}
+		if _, err := w.Add(path); err != nil {
+			t.Fatalf("w.Add failed: %v", err)
+		}
+		_, err = w.Commit(msg, &git.CommitOptions{
+			Author: &object.Signature{Name: "Test", Email: "[email protected]"},
+		})
+		if err != nil {
+			t.Fatalf("w.Commit failed: %v", err)
+		}
+	}
+
+	createAndCommit(pathAndMessages[0].path, pathAndMessages[0].message)
+	head, err := gitRepo.Head()
+	if err != nil {
+		t.Fatalf("repo.Head() failed: %v", err)
+	}
+	for _, tag := range tags {
+		if _, err := gitRepo.CreateTag(tag, head.Hash(), nil); err != nil {
+			t.Fatalf("CreateTag failed: %v", err)
+		}
+	}
+
+	for _, pam := range pathAndMessages[1:] {
+		createAndCommit(pam.path, pam.message)
+	}
+
+	r, err := gitrepo.NewRepository(&gitrepo.RepositoryOptions{Dir: dir})
+	if err != nil {
+		t.Fatalf("gitrepo.NewRepository failed: %v", err)
+	}
+	return r
+}
+
+type pathAndMessage struct {
+	path    string
+	message string
+}