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>

modules/git/git.go

@@ -37,6 +37,9 @@ var (
 
 	// will be checked on Init
 	goVersionLessThan115 = true
+
+	// SupportProcReceive version >= 2.29.0
+	SupportProcReceive bool
 )
 
 // LocalVersion returns current Git version from shell.
@@ -183,6 +186,19 @@ func Init(ctx context.Context) error {
 		}
 	}
 
+	if CheckGitVersionAtLeast("2.29") == nil {
+		// set support for AGit flow
+		if err := checkAndAddConfig("receive.procReceiveRefs", "refs/for"); err != nil {
+			return err
+		}
+		SupportProcReceive = true
+	} else {
+		if err := checkAndRemoveConfig("receive.procReceiveRefs", "refs/for"); err != nil {
+			return err
+		}
+		SupportProcReceive = false
+	}
+
 	if runtime.GOOS == "windows" {
 		if err := checkAndSetConfig("core.longpaths", "true", true); err != nil {
 			return err
@@ -232,6 +248,51 @@ func checkAndSetConfig(key, defaultValue string, forceToDefault bool) error {
 	return nil
 }
 
+func checkAndAddConfig(key, value string) error {
+	_, stderr, err := process.GetManager().Exec("git.Init(get setting)", GitExecutable, "config", "--get", key, value)
+	if err != nil {
+		perr, ok := err.(*process.Error)
+		if !ok {
+			return fmt.Errorf("Failed to get git %s(%v) errType %T: %s", key, err, err, stderr)
+		}
+		eerr, ok := perr.Err.(*exec.ExitError)
+		if !ok || eerr.ExitCode() != 1 {
+			return fmt.Errorf("Failed to get git %s(%v) errType %T: %s", key, err, err, stderr)
+		}
+		if eerr.ExitCode() == 1 {
+			if _, stderr, err = process.GetManager().Exec(fmt.Sprintf("git.Init(set %s)", key), "git", "config", "--global", "--add", key, value); err != nil {
+				return fmt.Errorf("Failed to set git %s(%s): %s", key, err, stderr)
+			}
+			return nil
+		}
+	}
+
+	return nil
+}
+
+func checkAndRemoveConfig(key, value string) error {
+	_, stderr, err := process.GetManager().Exec("git.Init(get setting)", GitExecutable, "config", "--get", key, value)
+	if err != nil {
+		perr, ok := err.(*process.Error)
+		if !ok {
+			return fmt.Errorf("Failed to get git %s(%v) errType %T: %s", key, err, err, stderr)
+		}
+		eerr, ok := perr.Err.(*exec.ExitError)
+		if !ok || eerr.ExitCode() != 1 {
+			return fmt.Errorf("Failed to get git %s(%v) errType %T: %s", key, err, err, stderr)
+		}
+		if eerr.ExitCode() == 1 {
+			return nil
+		}
+	}
+
+	if _, stderr, err = process.GetManager().Exec(fmt.Sprintf("git.Init(set %s)", key), "git", "config", "--global", "--unset-all", key, value); err != nil {
+		return fmt.Errorf("Failed to set git %s(%s): %s", key, err, stderr)
+	}
+
+	return nil
+}
+
 // Fsck verifies the connectivity and validity of the objects in the database
 func Fsck(ctx context.Context, repoPath string, timeout time.Duration, args ...string) error {
 	// Make sure timeout makes sense.