1 files changed, 89 insertions, 19 deletions

diff --git a/services/pull/merge_rebase.go b/services/pull/merge_rebase.go
index d3bb86d4aa..a88f805ef0 100644
--- a/services/pull/merge_rebase.go
+++ b/services/pull/merge_rebase.go
@@ -5,13 +5,99 @@ package pull
 
 import (
 	"fmt"
+	"strings"
 
 	repo_model "code.gitea.io/gitea/models/repo"
 	"code.gitea.io/gitea/modules/git"
 	"code.gitea.io/gitea/modules/log"
 )
 
-// doMergeStyleRebase rebaases the tracking branch on the base branch as the current HEAD with or with a merge commit to the original pr branch
+// getRebaseAmendMessage composes the message to amend commits in rebase merge of a pull request.
+func getRebaseAmendMessage(ctx *mergeContext, baseGitRepo *git.Repository) (message string, err error) {
+	// Get existing commit message.
+	commitMessage, _, err := git.NewCommand(ctx, "show", "--format=%B", "-s").RunStdString(&git.RunOpts{Dir: ctx.tmpBasePath})
+	if err != nil {
+		return "", err
+	}
+
+	commitTitle, commitBody, _ := strings.Cut(commitMessage, "\n")
+	extraVars := map[string]string{"CommitTitle": strings.TrimSpace(commitTitle), "CommitBody": strings.TrimSpace(commitBody)}
+
+	message, body, err := getMergeMessage(ctx, baseGitRepo, ctx.pr, repo_model.MergeStyleRebase, extraVars)
+	if err != nil || message == "" {
+		return "", err
+	}
+
+	if len(body) > 0 {
+		message = message + "\n\n" + body
+	}
+	return message, err
+}
+
+// Perform rebase merge without merge commit.
+func doMergeRebaseFastForward(ctx *mergeContext) error {
+	baseHeadSHA, err := git.GetFullCommitID(ctx, ctx.tmpBasePath, "HEAD")
+	if err != nil {
+		return fmt.Errorf("Failed to get full commit id for HEAD: %w", err)
+	}
+
+	cmd := git.NewCommand(ctx, "merge", "--ff-only").AddDynamicArguments(stagingBranch)
+	if err := runMergeCommand(ctx, repo_model.MergeStyleRebase, cmd); err != nil {
+		log.Error("Unable to merge staging into base: %v", err)
+		return err
+	}
+
+	// Check if anything actually changed before we amend the message, fast forward can skip commits.
+	newMergeHeadSHA, err := git.GetFullCommitID(ctx, ctx.tmpBasePath, "HEAD")
+	if err != nil {
+		return fmt.Errorf("Failed to get full commit id for HEAD: %w", err)
+	}
+	if baseHeadSHA == newMergeHeadSHA {
+		return nil
+	}
+
+	// Original repo to read template from.
+	baseGitRepo, err := git.OpenRepository(ctx, ctx.pr.BaseRepo.RepoPath())
+	if err != nil {
+		log.Error("Unable to get Git repo for rebase: %v", err)
+		return err
+	}
+	defer baseGitRepo.Close()
+
+	// Amend last commit message based on template, if one exists
+	newMessage, err := getRebaseAmendMessage(ctx, baseGitRepo)
+	if err != nil {
+		log.Error("Unable to get commit message for amend: %v", err)
+		return err
+	}
+
+	if newMessage != "" {
+		if err := git.NewCommand(ctx, "commit", "--amend").AddOptionFormat("--message=%s", newMessage).Run(&git.RunOpts{Dir: ctx.tmpBasePath}); err != nil {
+			log.Error("Unable to amend commit message: %v", err)
+			return err
+		}
+	}
+
+	return nil
+}
+
+// Perform rebase merge with merge commit.
+func doMergeRebaseMergeCommit(ctx *mergeContext, message string) error {
+	cmd := git.NewCommand(ctx, "merge").AddArguments("--no-ff", "--no-commit").AddDynamicArguments(stagingBranch)
+
+	if err := runMergeCommand(ctx, repo_model.MergeStyleRebaseMerge, cmd); err != nil {
+		log.Error("Unable to merge staging into base: %v", err)
+		return err
+	}
+	if err := commitAndSignNoAuthor(ctx, message); err != nil {
+		log.Error("Unable to make final commit: %v", err)
+		return err
+	}
+
+	return nil
+}
+
+// doMergeStyleRebase rebases the tracking branch on the base branch as the current HEAD with or with a merge commit to the original pr branch
 func doMergeStyleRebase(ctx *mergeContext, mergeStyle repo_model.MergeStyle, message string) error {
 	if err := rebaseTrackingOnToBase(ctx, mergeStyle); err != nil {
 		return err
@@ -26,25 +112,9 @@ func doMergeStyleRebase(ctx *mergeContext, mergeStyle repo_model.MergeStyle, mes
 	ctx.outbuf.Reset()
 	ctx.errbuf.Reset()
 
-	cmd := git.NewCommand(ctx, "merge")
 	if mergeStyle == repo_model.MergeStyleRebase {
-		cmd.AddArguments("--ff-only")
-	} else {
-		cmd.AddArguments("--no-ff", "--no-commit")
-	}
-	cmd.AddDynamicArguments(stagingBranch)
-
-	// Prepare merge with commit
-	if err := runMergeCommand(ctx, mergeStyle, cmd); err != nil {
-		log.Error("Unable to merge staging into base: %v", err)
-		return err
-	}
-	if mergeStyle == repo_model.MergeStyleRebaseMerge {
-		if err := commitAndSignNoAuthor(ctx, message); err != nil {
-			log.Error("Unable to make final commit: %v", err)
-			return err
-		}
+		return doMergeRebaseFastForward(ctx)
 	}
 
-	return nil
+	return doMergeRebaseMergeCommit(ctx, message)
 }