1 files changed, 107 insertions, 0 deletions

diff --git a/services/pull/update_rebase.go b/services/pull/update_rebase.go
new file mode 100644
index 000000000..8e7bfa0ff
--- /dev/null
+++ b/services/pull/update_rebase.go
@@ -0,0 +1,107 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package pull
+
+import (
+	"context"
+	"fmt"
+	"strings"
+
+	issues_model "code.gitea.io/gitea/models/issues"
+	repo_model "code.gitea.io/gitea/models/repo"
+	user_model "code.gitea.io/gitea/models/user"
+	"code.gitea.io/gitea/modules/git"
+	"code.gitea.io/gitea/modules/log"
+	repo_module "code.gitea.io/gitea/modules/repository"
+	"code.gitea.io/gitea/modules/setting"
+)
+
+// updateHeadByRebaseOnToBase handles updating a PR's head branch by rebasing it on the PR current base branch
+func updateHeadByRebaseOnToBase(ctx context.Context, pr *issues_model.PullRequest, doer *user_model.User, message string) error {
+	// "Clone" base repo and add the cache headers for the head repo and branch
+	mergeCtx, cancel, err := createTemporaryRepoForMerge(ctx, pr, doer, "")
+	if err != nil {
+		return err
+	}
+	defer cancel()
+
+	// Determine the old merge-base before the rebase - we use this for LFS push later on
+	oldMergeBase, _, _ := git.NewCommand(ctx, "merge-base").AddDashesAndList(baseBranch, trackingBranch).RunStdString(&git.RunOpts{Dir: mergeCtx.tmpBasePath})
+	oldMergeBase = strings.TrimSpace(oldMergeBase)
+
+	// Rebase the tracking branch on to the base as the staging branch
+	if err := rebaseTrackingOnToBase(mergeCtx, repo_model.MergeStyleRebaseUpdate); err != nil {
+		return err
+	}
+
+	if setting.LFS.StartServer {
+		// Now we need to ensure that the head repository contains any LFS objects between the new base and the old mergebase
+		// It's questionable about where this should go - either after or before the push
+		// I think in the interests of data safety - failures to push to the lfs should prevent
+		// the push as you can always re-rebase.
+		if err := LFSPush(ctx, mergeCtx.tmpBasePath, baseBranch, oldMergeBase, &issues_model.PullRequest{
+			HeadRepoID: pr.BaseRepoID,
+			BaseRepoID: pr.HeadRepoID,
+		}); err != nil {
+			log.Error("Unable to push lfs objects between %s and %s up to head branch in %-v: %v", baseBranch, oldMergeBase, pr, err)
+			return err
+		}
+	}
+
+	// Now determine who the pushing author should be
+	var headUser *user_model.User
+	if err := pr.HeadRepo.LoadOwner(ctx); err != nil {
+		if !user_model.IsErrUserNotExist(err) {
+			log.Error("Can't find user: %d for head repository in %-v - %v", pr.HeadRepo.OwnerID, pr, err)
+			return err
+		}
+		log.Error("Can't find user: %d for head repository in %-v - defaulting to doer: %-v - %v", pr.HeadRepo.OwnerID, pr, doer, err)
+		headUser = doer
+	} else {
+		headUser = pr.HeadRepo.Owner
+	}
+
+	pushCmd := git.NewCommand(ctx, "push", "-f", "head_repo").
+		AddDynamicArguments(stagingBranch + ":" + git.BranchPrefix + pr.HeadBranch)
+
+	// Push back to the head repository.
+	// TODO: this cause an api call to "/api/internal/hook/post-receive/...",
+	//       that prevents us from doint the whole merge in one db transaction
+	mergeCtx.outbuf.Reset()
+	mergeCtx.errbuf.Reset()
+
+	if err := pushCmd.Run(&git.RunOpts{
+		Env: repo_module.FullPushingEnvironment(
+			headUser,
+			doer,
+			pr.HeadRepo,
+			pr.HeadRepo.Name,
+			pr.ID,
+		),
+		Dir:    mergeCtx.tmpBasePath,
+		Stdout: mergeCtx.outbuf,
+		Stderr: mergeCtx.errbuf,
+	}); err != nil {
+		if strings.Contains(mergeCtx.errbuf.String(), "non-fast-forward") {
+			return &git.ErrPushOutOfDate{
+				StdOut: mergeCtx.outbuf.String(),
+				StdErr: mergeCtx.errbuf.String(),
+				Err:    err,
+			}
+		} else if strings.Contains(mergeCtx.errbuf.String(), "! [remote rejected]") {
+			err := &git.ErrPushRejected{
+				StdOut: mergeCtx.outbuf.String(),
+				StdErr: mergeCtx.errbuf.String(),
+				Err:    err,
+			}
+			err.GenerateMessage()
+			return err
+		}
+		return fmt.Errorf("git push: %s", mergeCtx.errbuf.String())
+	}
+	mergeCtx.outbuf.Reset()
+	mergeCtx.errbuf.Reset()
+
+	return nil
+}