feat: get commit history since last library generation (#1837)

Fixes #1706

Author: JoeWang1127

internal/gitrepo/gitrepo.go

@@ -39,6 +39,7 @@ type Repository interface {
 	HeadHash() (string, error)
 	ChangedFilesInCommit(commitHash string) ([]string, error)
 	GetCommitsForPathsSinceTag(paths []string, tagName string) ([]*Commit, error)
+	GetCommitsForPathsSinceCommit(paths []string, sinceCommit string) ([]*Commit, error)
 	CreateBranchAndCheckout(name string) error
 	Push(branchName string) error
 }

internal/librarian/command.go

@@ -26,6 +26,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/googleapis/librarian/internal/conventionalcommits"
+
 	"github.com/googleapis/librarian/internal/docker"
 
 	"github.com/googleapis/librarian/internal/config"
@@ -276,6 +278,27 @@ func copyLibrary(dst, src string, library *config.LibraryState) error {
 	return nil
 }
 
+func coerceLibraryChanges(commits []*conventionalcommits.ConventionalCommit) []*config.Change {
+	changes := make([]*config.Change, 0)
+	for _, commit := range commits {
+		clNum := ""
+		if cl, ok := commit.Footers[KeyClNum]; ok {
+			clNum = cl
+		}
+
+		changeType := getChangeType(commit)
+		changes = append(changes, &config.Change{
+			Type:       changeType,
+			Subject:    commit.Description,
+			Body:       commit.Body,
+			ClNum:      clNum,
+			CommitHash: commit.SHA,
+		})
+	}
+
+	return changes
+}
+
 // commitAndPush creates a commit and push request to GitHub for the generated
 // changes.
 // It uses the GitHub client to create a PR with the specified branch, title, and

internal/librarian/generate.go

@@ -190,7 +190,7 @@ func (r *generateRunner) generateSingleLibrary(ctx context.Context, libraryID, o
 	// libraries interfering with each other, and makes it easier to see what
 	// was generated for each library when debugging.
 	libraryOutputDir := filepath.Join(outputDir, libraryID)
-	if err := os.Mkdir(libraryOutputDir, 0755); err != nil {
+	if err := os.MkdirAll(libraryOutputDir, 0755); err != nil {
 		return err
 	}
 
@@ -199,6 +199,10 @@ func (r *generateRunner) generateSingleLibrary(ctx context.Context, libraryID, o
 		return err
 	}
 
+	if err := r.updateChangesSinceLastGeneration(generatedLibraryID); err != nil {
+		return err
+	}
+
 	if err := r.runBuildCommand(ctx, generatedLibraryID); err != nil {
 		return err
 	}
@@ -212,6 +216,21 @@ func (r *generateRunner) needsConfigure() bool {
 	return r.cfg.API != "" && r.cfg.Library != "" && findLibraryByID(r.state, r.cfg.Library) == nil
 }
 
+func (r *generateRunner) updateChangesSinceLastGeneration(libraryID string) error {
+	for _, library := range r.state.Libraries {
+		if library.ID == libraryID {
+			commits, err := GetConventionalCommitsSinceLastGeneration(r.repo, library)
+			if err != nil {
+				return fmt.Errorf("failed to fetch conventional commits for library, %s: %w", library.ID, err)
+			}
+			library.Changes = coerceLibraryChanges(commits)
+			break
+		}
+	}
+
+	return nil
+}
+
 func (r *generateRunner) updateLastGeneratedCommitState(libraryID string) error {
 	hash, err := r.sourceRepo.HeadHash()
 	if err != nil {