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>

1 files changed, 11 insertions, 3 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 {