Use GitHub-style commit message for squash merge (#35987)

services/pull/pull.go

@@ -13,6 +13,7 @@ import (
 	"regexp"
 	"strings"
 	"time"
+	"unicode/utf8"
 
 	"code.gitea.io/gitea/models/db"
 	git_model "code.gitea.io/gitea/models/git"
@@ -838,51 +839,53 @@ func GetSquashMergeCommitMessages(ctx context.Context, pr *issues_model.PullRequ
 	stringBuilder := strings.Builder{}
 
 	if !setting.Repository.PullRequest.PopulateSquashCommentWithCommitMessages {
+		// use PR's title and description as squash commit message
 		message := strings.TrimSpace(pr.Issue.Content)
 		stringBuilder.WriteString(message)
 		if stringBuilder.Len() > 0 {
 			stringBuilder.WriteRune('\n')
 			if !commitMessageTrailersPattern.MatchString(message) {
+				// TODO: this trailer check doesn't work with the separator line added below for the co-authors
 				stringBuilder.WriteRune('\n')
 			}
 		}
+	} else {
+		// use PR's commit messages as squash commit message
+		// commits list is in reverse chronological order
+		maxMsgSize := setting.Repository.PullRequest.DefaultMergeMessageSize
+		for i := len(commits) - 1; i >= 0; i-- {
+			commit := commits[i]
+			msg := strings.TrimSpace(commit.CommitMessage)
+			if msg == "" {
+				continue
+			}
+
+			// This format follows GitHub's squash commit message style,
+			// even if there are other "* " in the commit message body, they are written as-is.
+			// Maybe, ideally, we should indent those lines too.
+			_, _ = fmt.Fprintf(&stringBuilder, "* %s\n\n", msg)
+			if maxMsgSize > 0 && stringBuilder.Len() >= maxMsgSize {
+				tmp := stringBuilder.String()
+				wasValidUtf8 := utf8.ValidString(tmp)
+				tmp = tmp[:maxMsgSize] + "..."
+				if wasValidUtf8 {
+					// If the message was valid UTF-8 before truncation, ensure it remains valid after truncation
+					// For non-utf8 messages, we can't do much about it, end users should use utf-8 as much as possible
+					tmp = strings.ToValidUTF8(tmp, "")
+				}
+				stringBuilder.Reset()
+				stringBuilder.WriteString(tmp)
+				break
+			}
+		}
 	}
 
-	// commits list is in reverse chronological order
-	first := true
-	for i := len(commits) - 1; i >= 0; i-- {
-		commit := commits[i]
-
-		if setting.Repository.PullRequest.PopulateSquashCommentWithCommitMessages {
-			maxSize := setting.Repository.PullRequest.DefaultMergeMessageSize
-			if maxSize < 0 || stringBuilder.Len() < maxSize {
-				var toWrite []byte
-				if first {
-					first = false
-					toWrite = []byte(strings.TrimPrefix(commit.CommitMessage, pr.Issue.Title))
-				} else {
-					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 ""
-				}
-			}
-		}
-
+	// collect co-authors
+	for _, commit := range commits {
 		authorString := commit.Author.String()
 		if uniqueAuthors.Add(authorString) && authorString != posterSig {
 			// Compare use account as well to avoid adding the same author multiple times
-			// times when email addresses are private or multiple emails are used.
+			// when email addresses are private or multiple emails are used.
 			commitUser, _ := user_model.GetUserByEmail(ctx, commit.Author.Email)
 			if commitUser == nil || commitUser.ID != pr.Issue.Poster.ID {
 				authors = append(authors, authorString)
@@ -890,12 +893,12 @@ func GetSquashMergeCommitMessages(ctx context.Context, pr *issues_model.PullRequ
 		}
 	}
 
-	// Consider collecting the remaining authors
+	// collect the remaining authors
 	if limit >= 0 && setting.Repository.PullRequest.DefaultMergeMessageAllAuthors {
 		skip := limit
 		limit = 30
 		for {
-			commits, err := gitRepo.CommitsBetweenLimit(headCommit, mergeBase, limit, skip)
+			commits, err = gitRepo.CommitsBetweenLimit(headCommit, mergeBase, limit, skip)
 			if err != nil {
 				log.Error("Unable to get commits between: %s %s Error: %v", pr.HeadBranch, pr.MergeBase, err)
 				return ""
@@ -916,19 +919,15 @@ func GetSquashMergeCommitMessages(ctx context.Context, pr *issues_model.PullRequ
 		}
 	}
 
+	if stringBuilder.Len() > 0 && len(authors) > 0 {
+		// TODO: this separator line doesn't work with the trailer check (commitMessageTrailersPattern) above
+		stringBuilder.WriteString("---------\n\n")
+	}
+
 	for _, author := range authors {
-		if _, err := stringBuilder.WriteString("Co-authored-by: "); err != nil {
-			log.Error("Unable to write to string builder Error: %v", err)
-			return ""
-		}
-		if _, err := stringBuilder.WriteString(author); err != nil {
-			log.Error("Unable to write to string builder Error: %v", err)
-			return ""
-		}
-		if _, err := stringBuilder.WriteRune('\n'); err != nil {
-			log.Error("Unable to write to string builder Error: %v", err)
-			return ""
-		}
+		stringBuilder.WriteString("Co-authored-by: ")
+		stringBuilder.WriteString(author)
+		stringBuilder.WriteRune('\n')
 	}
 
 	return stringBuilder.String()