Don't create self-references in merged PRs (#36490)

Fixes: https://github.com/go-gitea/gitea/issues/36488
Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Giteabot <teabot@gitea.io>

services/issue/commit.go

@@ -89,6 +89,24 @@ func issueAddTime(ctx context.Context, issue *issues_model.Issue, doer *user_mod
 	return err
 }
 
+// isSelfReference checks if a commit is the merge commit of the PR it references.
+// This prevents creating self-referencing timeline entries when a PR merge commit
+// contains a reference to its own PR number in the commit message.
+func isSelfReference(ctx context.Context, issue *issues_model.Issue, commitSHA string) bool {
+	if !issue.IsPull {
+		return false
+	}
+
+	if err := issue.LoadPullRequest(ctx); err != nil {
+		if !issues_model.IsErrPullRequestNotExist(err) {
+			log.Error("LoadPullRequest: %v", err)
+		}
+		return false
+	}
+
+	return issue.PullRequest.MergedCommitID == commitSHA
+}
+
 // getIssueFromRef returns the issue referenced by a ref. Returns a nil *Issue
 // if the provided ref references a non-existent issue.
 func getIssueFromRef(ctx context.Context, repo *repo_model.Repository, index int64) (*issues_model.Issue, error) {
@@ -158,6 +176,11 @@ func UpdateIssuesCommit(ctx context.Context, doer *user_model.User, repo *repo_m
 				continue
 			}
 
+			// Skip self-references: if this commit is the merge commit of the PR it references
+			if isSelfReference(ctx, refIssue, c.Sha1) {
+				continue
+			}
+
 			message := fmt.Sprintf(`<a href="%s/commit/%s">%s</a>`, html.EscapeString(repo.Link()), html.EscapeString(url.PathEscape(c.Sha1)), html.EscapeString(strings.SplitN(c.Message, "\n", 2)[0]))
 			if err = CreateRefComment(ctx, doer, refRepo, refIssue, message, c.Sha1); err != nil {
 				if errors.Is(err, user_model.ErrBlockedUser) {

services/issue/commit_test.go

@@ -298,3 +298,59 @@ func TestUpdateIssuesCommit_AnotherRepoNoPermission(t *testing.T) {
 	unittest.AssertNotExistsBean(t, issueBean, "is_closed=1")
 	unittest.CheckConsistencyFor(t, &activities_model.Action{})
 }
+
+func TestUpdateIssuesCommit_SelfReference(t *testing.T) {
+	assert.NoError(t, unittest.PrepareTestDatabase())
+	user := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+
+	// Test that a PR merge commit that references its own PR does not create a self-reference comment
+	// PR #2 (issue_id=2) has merged_commit_id: 1a8823cd1a9549fde083f992f6b9b87a7ab74fb3
+	pushCommits := []*repository.PushCommit{
+		{
+			Sha1:           "1a8823cd1a9549fde083f992f6b9b87a7ab74fb3",
+			CommitterEmail: "user2@example.com",
+			CommitterName:  "User Two",
+			AuthorEmail:    "user2@example.com",
+			AuthorName:     "User Two",
+			Message:        "Merge pull request 'issue2' (#2) from branch1 into master",
+		},
+	}
+
+	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: 1})
+
+	selfRefCommentBean := &issues_model.Comment{
+		Type:      issues_model.CommentTypeCommitRef,
+		CommitSHA: "1a8823cd1a9549fde083f992f6b9b87a7ab74fb3",
+		PosterID:  user.ID,
+		IssueID:   2,
+	}
+
+	unittest.AssertNotExistsBean(t, selfRefCommentBean)
+	assert.NoError(t, UpdateIssuesCommit(t.Context(), user, repo, pushCommits, repo.DefaultBranch))
+	unittest.AssertNotExistsBean(t, selfRefCommentBean)
+	unittest.CheckConsistencyFor(t, &activities_model.Action{})
+
+	// Test that normal commit references are still created
+	pushCommits2 := []*repository.PushCommit{
+		{
+			Sha1:           "abcdef9876543210",
+			CommitterEmail: "user2@example.com",
+			CommitterName:  "User Two",
+			AuthorEmail:    "user2@example.com",
+			AuthorName:     "User Two",
+			Message:        "Fix bug, refs #1",
+		},
+	}
+
+	otherRefCommentBean := &issues_model.Comment{
+		Type:      issues_model.CommentTypeCommitRef,
+		CommitSHA: "abcdef9876543210",
+		PosterID:  user.ID,
+		IssueID:   1,
+	}
+
+	unittest.AssertNotExistsBean(t, otherRefCommentBean)
+	assert.NoError(t, UpdateIssuesCommit(t.Context(), user, repo, pushCommits2, repo.DefaultBranch))
+	unittest.AssertExistsAndLoadBean(t, otherRefCommentBean)
+	unittest.CheckConsistencyFor(t, &activities_model.Action{})
+}