1 files changed, 121 insertions, 0 deletions

diff --git a/services/pull/merge_rebase.go b/services/pull/merge_rebase.go
new file mode 100644
index 0000000..ecf3762
--- /dev/null
+++ b/services/pull/merge_rebase.go
@@ -0,0 +1,121 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pull
+
+import (
+	"fmt"
+	"strings"
+
+	repo_model "code.gitea.io/gitea/models/repo"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/gitrepo"
+	"code.gitea.io/gitea/modules/log"
+)
+
+// 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 := gitrepo.OpenRepository(ctx, ctx.pr.BaseRepo)
+	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
+	}
+
+	// Checkout base branch again
+	if err := git.NewCommand(ctx, "checkout").AddDynamicArguments(baseBranch).
+		Run(ctx.RunOpts()); err != nil {
+		log.Error("git checkout base prior to merge post staging rebase %-v: %v\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+		return fmt.Errorf("git checkout base prior to merge post staging rebase  %v: %w\n%s\n%s", ctx.pr, err, ctx.outbuf.String(), ctx.errbuf.String())
+	}
+	ctx.outbuf.Reset()
+	ctx.errbuf.Reset()
+
+	if mergeStyle == repo_model.MergeStyleRebase {
+		return doMergeRebaseFastForward(ctx)
+	}
+
+	return doMergeRebaseMergeCommit(ctx, message)
+}