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>

2 files changed, 26 insertions, 0 deletions

diff --git a/models/migrations/migrations.go b/models/migrations/migrations.go
index fed7b909c1..9b04a364ca 100644
--- a/models/migrations/migrations.go
+++ b/models/migrations/migrations.go
@@ -329,6 +329,8 @@ var migrations = []Migration{
 	NewMigration("Add key is verified to gpg key", addKeyIsVerified),
 	// v189 -> v190
 	NewMigration("Unwrap ldap.Sources", unwrapLDAPSourceCfg),
+	// v190 -> v191
+	NewMigration("Add agit flow pull request support", addAgitFlowPullRequest),
 }
 
 // GetCurrentDBVersion returns the current db version
diff --git a/models/migrations/v190.go b/models/migrations/v190.go
new file mode 100644
index 0000000000..8d1fba8373
--- /dev/null
+++ b/models/migrations/v190.go
@@ -0,0 +1,24 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package migrations
+
+import (
+	"fmt"
+
+	"xorm.io/xorm"
+)
+
+func addAgitFlowPullRequest(x *xorm.Engine) error {
+	type PullRequestFlow int
+
+	type PullRequest struct {
+		Flow PullRequestFlow `xorm:"NOT NULL DEFAULT 0"`
+	}
+
+	if err := x.Sync2(new(PullRequest)); err != nil {
+		return fmt.Errorf("sync2: %v", err)
+	}
+	return nil
+}