Use the text of pull-request as the squash commit's message (#13071)

Originally, it was filled by the commit messages of the involved
commits. In this change, we use the headline comment of the pull
request as the commit message when it is a squash merge.

Thanks to @zeripath for suggesting the idea.

Fixes #12365

Co-authored-by: Mura Li <typeless@users.noreply.github.com>

routers/repo/pull.go

@@ -440,7 +440,7 @@ func PrepareViewPullInfo(ctx *context.Context, issue *models.Issue) *git.Compare
  ctx.ServerError("IsUserAllowedToUpdate", err)
  return nil
  }
- ctx.Data["GetCommitMessages"] = pull_service.GetCommitMessages(pull)
+ ctx.Data["GetCommitMessages"] = pull_service.GetSquashMergeCommitMessages(pull)
  }
 
  sha, err := baseGitRepo.GetRefCommitID(pull.GetGitRefName())

services/pull/pull.go

@@ -502,8 +502,8 @@ func CloseRepoBranchesPulls(doer *models.User, repo *models.Repository) error {
  return nil
 }
 
-// GetCommitMessages returns the commit messages between head and merge base (if there is one)
-func GetCommitMessages(pr *models.PullRequest) string {
+// GetSquashMergeCommitMessages returns the commit messages between head and merge base (if there is one)
+func GetSquashMergeCommitMessages(pr *models.PullRequest) string {
  if err := pr.LoadIssue(); err != nil {
  log.Error("Cannot load issue %d for PR id %d: Error: %v", pr.IssueID, pr.ID, err)
  return ""
@@ -550,34 +550,22 @@ func GetCommitMessages(pr *models.PullRequest) string {
  return ""
  }
 
- maxSize := setting.Repository.PullRequest.DefaultMergeMessageSize
-
  posterSig := pr.Issue.Poster.NewGitSig().String()
 
  authorsMap := map[string]bool{}
  authors := make([]string, 0, list.Len())
  stringBuilder := strings.Builder{}
+
+ stringBuilder.WriteString(pr.Issue.Content)
+ if stringBuilder.Len() > 0 {
+ stringBuilder.WriteRune('\n')
+ stringBuilder.WriteRune('\n')
+ }
+
  // commits list is in reverse chronological order
  element := list.Back()
  for element != nil {
  commit := element.Value.(*git.Commit)
-
- if maxSize < 0 || stringBuilder.Len() < maxSize {
- toWrite := []byte(commit.CommitMessage)
- if len(toWrite) > maxSize-stringBuilder.Len() && maxSize > -1 {
- toWrite = append(toWrite[:maxSize-stringBuilder.Len()], "..."...)
- }
- if _, err := stringBuilder.Write(toWrite); err != nil {
- log.Error("Unable to write commit message Error: %v", err)
- return ""
- }
-
- if _, err := stringBuilder.WriteRune('\n'); err != nil {
- log.Error("Unable to write commit message Error: %v", err)
- return ""
- }
- }
-
  authorString := commit.Author.String()
  if !authorsMap[authorString] && authorString != posterSig {
  authors = append(authors, authorString)