fix(pulls): add branch-name option for DEFAULT_TITLE_SOURCE (#38356)

Adds a new `branch-name` value for the `[repository.pull-request]`
`DEFAULT_TITLE_SOURCE` setting that always uses the normalized branch
name as the PR title, regardless of commit count.

Fix #38317

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/web/repo/compare.go

@@ -383,7 +383,9 @@ func autoTitleFromBranchName(name string) string {
 
 func prepareNewPullRequestTitleContent(ci *git_service.CompareInfo, commits []*git_model.SignCommitWithStatuses, defaultTitleSource string) (title, content string) {
 	useFirstCommitAsTitle := len(commits) == 1 || (defaultTitleSource == setting.RepoPRTitleSourceFirstCommit && len(commits) > 0)
-	if useFirstCommitAsTitle {
+	if defaultTitleSource == setting.RepoPRTitleSourceBranchName {
+		title = ci.HeadRef.ShortName()
+	} else if useFirstCommitAsTitle {
 		// the "commits" are from "ShowPrettyFormatLogToList", which is ordered from newest to oldest, here take the oldest one
 		c := commits[len(commits)-1]
 		title = c.UserCommit.GitCommit.MessageTitle()

routers/web/repo/compare_test.go

@@ -70,6 +70,10 @@ func TestNewPullRequestTitleContent(t *testing.T) {
 	assert.Equal(t, "Head branch", title)
 	assert.Empty(t, content)
 
+	title, content = prepareNewPullRequestTitleContent(ci, nil, setting.RepoPRTitleSourceBranchName)
+	assert.Equal(t, "head-branch", title)
+	assert.Empty(t, content)
+
 	// single commit
 	title, content = prepareNewPullRequestTitleContent(ci, []*git_model.SignCommitWithStatuses{mockCommit("single-commit-title\nbody")}, setting.RepoPRTitleSourceAuto)
 	assert.Equal(t, "single-commit-title", title)