Add agit flow support in gitea (#14295)

* feature: add agit flow support

ref: https://git-repo.info/en/2020/03/agit-flow-and-git-repo/

example:

```Bash
git checkout -b test
echo "test" >> README.md
git commit -m "test"
git push origin HEAD:refs/for/master -o topic=test
```

Signed-off-by: a1012112796 <1012112796@qq.com>

* fix lint

* simplify code add fix some nits

* update merge help message

* Apply suggestions from code review. Thanks @jiangxin

* add forced-update message

* fix lint

* splite writePktLine

* add refs/for/<target-branch>/<topic-branch> support also

* Add test code add fix api

* fix lint

* fix test

* skip test if git version < 2.29

* try test with git 2.30.1

* fix permission check bug

* fix some nit

* logic implify and test code update

* fix bug

* apply suggestions from code review

* prepare for merge

Signed-off-by: Andrew Thornton <art27@cantab.net>

* fix permission check bug

- test code update
- apply suggestions from code review @zeripath

Signed-off-by: a1012112796 <1012112796@qq.com>

* fix bug when target branch isn't exist

* prevent some special push and fix some nits

* fix lint

* try splite

* Apply suggestions from code review

- fix permission check
- handle user rename

* fix version negotiation

* remane

* fix template

* handle empty repo

* ui: fix  branch link under the title

* fix nits

Co-authored-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

4 files changed, 84 insertions, 13 deletions

diff --git a/services/pull/commit_status.go b/services/pull/commit_status.go
index b8fb109440..c5c930ee0d 100644
--- a/services/pull/commit_status.go
+++ b/services/pull/commit_status.go
@@ -108,13 +108,21 @@ func GetPullRequestCommitStatusState(pr *models.PullRequest) (structs.CommitStat
 	}
 	defer headGitRepo.Close()
 
-	if !headGitRepo.IsBranchExist(pr.HeadBranch) {
+	if pr.Flow == models.PullRequestFlowGithub && !headGitRepo.IsBranchExist(pr.HeadBranch) {
+		return "", errors.New("Head branch does not exist, can not merge")
+	}
+	if pr.Flow == models.PullRequestFlowAGit && !git.IsReferenceExist(headGitRepo.Path, pr.GetGitRefName()) {
 		return "", errors.New("Head branch does not exist, can not merge")
 	}
 
-	sha, err := headGitRepo.GetBranchCommitID(pr.HeadBranch)
+	var sha string
+	if pr.Flow == models.PullRequestFlowGithub {
+		sha, err = headGitRepo.GetBranchCommitID(pr.HeadBranch)
+	} else {
+		sha, err = headGitRepo.GetRefCommitID(pr.GetGitRefName())
+	}
 	if err != nil {
-		return "", errors.Wrap(err, "GetBranchCommitID")
+		return "", err
 	}
 
 	if err := pr.LoadBaseRepo(); err != nil {
diff --git a/services/pull/pull.go b/services/pull/pull.go
index 6c108c224f..b33f641130 100644
--- a/services/pull/pull.go
+++ b/services/pull/pull.go
@@ -49,7 +49,12 @@ func NewPullRequest(repo *models.Repository, pull *models.Issue, labelIDs []int6
 	pr.Issue = pull
 	pull.PullRequest = pr
 
-	if err := PushToBaseRepo(pr); err != nil {
+	if pr.Flow == models.PullRequestFlowGithub {
+		err = PushToBaseRepo(pr)
+	} else {
+		err = UpdateRef(pr)
+	}
+	if err != nil {
 		return err
 	}
 
@@ -145,7 +150,7 @@ func ChangeTargetBranch(pr *models.PullRequest, doer *models.User, targetBranch
 	}
 
 	// Check if pull request for the new target branch already exists
-	existingPr, err := models.GetUnmergedPullRequest(pr.HeadRepoID, pr.BaseRepoID, pr.HeadBranch, targetBranch)
+	existingPr, err := models.GetUnmergedPullRequest(pr.HeadRepoID, pr.BaseRepoID, pr.HeadBranch, targetBranch, models.PullRequestFlowGithub)
 	if existingPr != nil {
 		return models.ErrPullRequestAlreadyExists{
 			ID:         existingPr.ID,
@@ -281,8 +286,12 @@ func AddTestPullRequestTask(doer *models.User, repoID int64, branch string, isSy
 
 		for _, pr := range prs {
 			log.Trace("Updating PR[%d]: composing new test task", pr.ID)
-			if err := PushToBaseRepo(pr); err != nil {
-				log.Error("PushToBaseRepo: %v", err)
+			if pr.Flow == models.PullRequestFlowGithub {
+				if err := PushToBaseRepo(pr); err != nil {
+					log.Error("PushToBaseRepo: %v", err)
+					continue
+				}
+			} else {
 				continue
 			}
 
@@ -451,6 +460,22 @@ func pushToBaseRepoHelper(pr *models.PullRequest, prefixHeadBranch string) (err
 	return nil
 }
 
+// UpdateRef update refs/pull/id/head directly for agit flow pull request
+func UpdateRef(pr *models.PullRequest) (err error) {
+	log.Trace("UpdateRef[%d]: upgate pull request ref in base repo '%s'", pr.ID, pr.GetGitRefName())
+	if err := pr.LoadBaseRepo(); err != nil {
+		log.Error("Unable to load base repository for PR[%d] Error: %v", pr.ID, err)
+		return err
+	}
+
+	_, err = git.NewCommand("update-ref", pr.GetGitRefName(), pr.HeadCommitID).RunInDir(pr.BaseRepo.RepoPath())
+	if err != nil {
+		log.Error("Unable to update ref in base repository for PR[%d] Error: %v", pr.ID, err)
+	}
+
+	return err
+}
+
 type errlist []error
 
 func (errs errlist) Error() string {
@@ -562,7 +587,17 @@ func GetSquashMergeCommitMessages(pr *models.PullRequest) string {
 	}
 	defer gitRepo.Close()
 
-	headCommit, err := gitRepo.GetBranchCommit(pr.HeadBranch)
+	var headCommit *git.Commit
+	if pr.Flow == models.PullRequestFlowGithub {
+		headCommit, err = gitRepo.GetBranchCommit(pr.HeadBranch)
+	} else {
+		pr.HeadCommitID, err = gitRepo.GetRefCommitID(pr.GetGitRefName())
+		if err != nil {
+			log.Error("Unable to get head commit: %s Error: %v", pr.GetGitRefName(), err)
+			return ""
+		}
+		headCommit, err = gitRepo.GetCommit(pr.HeadCommitID)
+	}
 	if err != nil {
 		log.Error("Unable to get head commit: %s Error: %v", pr.HeadBranch, err)
 		return ""
@@ -781,9 +816,20 @@ func IsHeadEqualWithBranch(pr *models.PullRequest, branchName string) (bool, err
 	}
 	defer headGitRepo.Close()
 
-	headCommit, err := headGitRepo.GetBranchCommit(pr.HeadBranch)
-	if err != nil {
-		return false, err
+	var headCommit *git.Commit
+	if pr.Flow == models.PullRequestFlowGithub {
+		headCommit, err = headGitRepo.GetBranchCommit(pr.HeadBranch)
+		if err != nil {
+			return false, err
+		}
+	} else {
+		pr.HeadCommitID, err = baseGitRepo.GetRefCommitID(pr.GetGitRefName())
+		if err != nil {
+			return false, err
+		}
+		if headCommit, err = baseGitRepo.GetCommit(pr.HeadCommitID); err != nil {
+			return false, err
+		}
 	}
 	return baseCommit.HasPreviousCommit(headCommit.ID)
 }
diff --git a/services/pull/temp_repo.go b/services/pull/temp_repo.go
index 19b488790a..54d09c8158 100644
--- a/services/pull/temp_repo.go
+++ b/services/pull/temp_repo.go
@@ -140,7 +140,15 @@ func createTemporaryRepo(pr *models.PullRequest) (string, error) {
 
 	trackingBranch := "tracking"
 	// Fetch head branch
-	if err := git.NewCommand("fetch", "--no-tags", remoteRepoName, git.BranchPrefix+pr.HeadBranch+":"+trackingBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
+	var headBranch string
+	if pr.Flow == models.PullRequestFlowGithub {
+		headBranch = git.BranchPrefix + pr.HeadBranch
+	} else if len(pr.HeadCommitID) == 40 { // for not created pull request
+		headBranch = pr.HeadCommitID
+	} else {
+		headBranch = pr.GetGitRefName()
+	}
+	if err := git.NewCommand("fetch", "--no-tags", remoteRepoName, headBranch+":"+trackingBranch).RunInDirPipeline(tmpBasePath, &outbuf, &errbuf); err != nil {
 		if err := models.RemoveTemporaryPath(tmpBasePath); err != nil {
 			log.Error("CreateTempRepo: RemoveTemporaryPath: %s", err)
 		}
@@ -150,7 +158,7 @@ func createTemporaryRepo(pr *models.PullRequest) (string, error) {
 			}
 		}
 		log.Error("Unable to fetch head_repo head branch [%s:%s -> tracking in %s]: %v:\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, tmpBasePath, err, outbuf.String(), errbuf.String())
-		return "", fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), pr.HeadBranch, err, outbuf.String(), errbuf.String())
+		return "", fmt.Errorf("Unable to fetch head_repo head branch [%s:%s -> tracking in tmpBasePath]: %v\n%s\n%s", pr.HeadRepo.FullName(), headBranch, err, outbuf.String(), errbuf.String())
 	}
 	outbuf.Reset()
 	errbuf.Reset()
diff --git a/services/pull/update.go b/services/pull/update.go
index f35e47cbf8..c2c13845e3 100644
--- a/services/pull/update.go
+++ b/services/pull/update.go
@@ -22,6 +22,11 @@ func Update(pull *models.PullRequest, doer *models.User, message string) error {
 		BaseBranch: pull.HeadBranch,
 	}
 
+	if pull.Flow == models.PullRequestFlowAGit {
+		// TODO: Not support update agit flow pull request's head branch
+		return fmt.Errorf("Not support update agit flow pull request's head branch")
+	}
+
 	if err := pr.LoadHeadRepo(); err != nil {
 		log.Error("LoadHeadRepo: %v", err)
 		return fmt.Errorf("LoadHeadRepo: %v", err)
@@ -48,6 +53,10 @@ func Update(pull *models.PullRequest, doer *models.User, message string) error {
 
 // IsUserAllowedToUpdate check if user is allowed to update PR with given permissions and branch protections
 func IsUserAllowedToUpdate(pull *models.PullRequest, user *models.User) (bool, error) {
+	if pull.Flow == models.PullRequestFlowAGit {
+		return false, nil
+	}
+
 	if user == nil {
 		return false, nil
 	}