feat(api): add in_reply_to field for pull review comment replies

Add `in_reply_to` field to `CreatePullReviewComment` that accepts a
comment ID, consistent with GitHub's API. The handler resolves the
comment ID to the internal review ID and creates the reply as a
non-pending comment so it threads correctly under the original review.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

modules/structs/pull_review.go

@@ -89,6 +89,8 @@ type CreatePullReviewComment struct {
 	OldLineNum int64 `json:"old_position"`
 	// if comment to new file line or 0
 	NewLineNum int64 `json:"new_position"`
+	// if replying to an existing review comment, the comment ID to reply to
+	InReplyToID int64 `json:"in_reply_to_id"`
 }
 
 // SubmitPullReviewOptions are options to submit a pending pull request review

routers/api/v1/repo/pull_review.go

@@ -388,6 +388,34 @@ func DeletePullReview(ctx *context.APIContext) {
 	ctx.Status(http.StatusNoContent)
 }
 
+// resolveInReplyTo resolves an in_reply_to comment ID to the review ID it
+// belongs to. Returns 0 when commentID is 0 (not a reply).
+func resolveInReplyTo(ctx *context.APIContext, commentID int64, pr *issues_model.PullRequest) (int64, error) {
+	if commentID == 0 {
+		return 0, nil
+	}
+	comment, err := issues_model.GetCommentByID(ctx, commentID)
+	if err != nil {
+		if issues_model.IsErrCommentNotExist(err) {
+			ctx.APIErrorNotFound("GetCommentByID", err)
+		} else {
+			ctx.APIErrorInternal(err)
+		}
+		return 0, err
+	}
+	if comment.IssueID != pr.IssueID {
+		err := issues_model.ErrCommentNotExist{ID: commentID}
+		ctx.APIErrorNotFound("GetCommentByID", err)
+		return 0, err
+	}
+	if comment.Type != issues_model.CommentTypeCode || comment.ReviewID == 0 {
+		err := errors.New("comment is not a review comment")
+		ctx.APIError(http.StatusUnprocessableEntity, err)
+		return 0, err
+	}
+	return comment.ReviewID, nil
+}
+
 // CreatePullReview create a review to a pull request
 func CreatePullReview(ctx *context.APIContext) {
 	// swagger:operation POST /repos/{owner}/{repo}/pulls/{index}/reviews repository repoCreatePullReview
@@ -466,12 +494,21 @@ func CreatePullReview(ctx *context.APIContext) {
 	}
 
 	// create review comments
+	var lastReplyReviewID int64
 	for _, c := range opts.Comments {
 		line := c.NewLineNum
 		if c.OldLineNum > 0 {
 			line = c.OldLineNum * -1
 		}
 
+		replyReviewID, err := resolveInReplyTo(ctx, c.InReplyToID, pr)
+		if err != nil {
+			return
+		}
+		if replyReviewID != 0 {
+			lastReplyReviewID = replyReviewID
+		}
+
 		if _, err := pull_service.CreateCodeComment(ctx,
 			ctx.Doer,
 			ctx.Repo.GitRepo,
@@ -479,8 +516,8 @@ func CreatePullReview(ctx *context.APIContext) {
 			line,
 			c.Body,
 			c.Path,
-			true, // pending review
-			0,    // no reply
+			replyReviewID == 0, // pending
+			replyReviewID,      // reply
 			opts.CommitID,
 			nil,
 		); err != nil {
@@ -491,6 +528,10 @@ func CreatePullReview(ctx *context.APIContext) {
 
 	// create review and associate all pending review comments
 	review, _, err := pull_service.SubmitReview(ctx, ctx.Doer, ctx.Repo.GitRepo, pr.Issue, reviewType, opts.Body, opts.CommitID, nil)
+	// reply-only requests have no pending review, fall back to the reply's review
+	if issues_model.IsContentEmptyErr(err) && lastReplyReviewID != 0 {
+		review, err = issues_model.GetReviewByID(ctx, lastReplyReviewID)
+	}
 	if err != nil {
 		if errors.Is(err, pull_service.ErrSubmitReviewOnClosedPR) {
 			ctx.APIError(http.StatusUnprocessableEntity, err)

templates/swagger/v1_json.tmpl

@@ -23615,6 +23615,12 @@
           "type": "string",
           "x-go-name": "Body"
         },
+        "in_reply_to_id": {
+          "description": "if replying to an existing review comment, the comment ID to reply to",
+          "type": "integer",
+          "format": "int64",
+          "x-go-name": "InReplyToID"
+        },
         "new_position": {
           "description": "if comment to new file line or 0",
           "type": "integer",

tests/integration/api_pull_review_test.go

@@ -530,6 +530,48 @@ func TestAPIPullReviewStayDismissed(t *testing.T) {
 		pullIssue.ID, user8.ID, 2, 0, 3, false)
 }
 
+func TestAPIPullReviewCommentReply(t *testing.T) {
+	defer tests.PrepareTestEnv(t)()
+
+	pullIssue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 3})
+	require.NoError(t, pullIssue.LoadRepo(t.Context()))
+	require.NoError(t, pullIssue.LoadPullRequest(t.Context()))
+	doer := unittest.AssertExistsAndLoadBean(t, &user_model.User{ID: 2})
+	gitRepo, err := gitrepo.OpenRepository(t.Context(), pullIssue.Repo)
+	require.NoError(t, err)
+	defer gitRepo.Close()
+
+	commitID, err := gitRepo.GetRefCommitID(pullIssue.PullRequest.GetGitHeadRefName())
+	require.NoError(t, err)
+
+	// create an initial code comment to reply to
+	originalComment, err := pull_service.CreateCodeComment(t.Context(), doer, gitRepo, pullIssue, 1, "original comment", "README.md", false, 0, commitID, nil)
+	require.NoError(t, err)
+
+	session := loginUser(t, doer.Name)
+	token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
+
+	req := NewRequestWithJSON(t, http.MethodPost, fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/reviews", pullIssue.Repo.OwnerName, pullIssue.Repo.Name, pullIssue.Index), &api.CreatePullReviewOptions{
+		Event: "COMMENT",
+		Comments: []api.CreatePullReviewComment{{
+			Path: "README.md", Body: "reply to original", NewLineNum: 1, InReplyToID: originalComment.ID,
+		}},
+	}).AddTokenAuth(token)
+	resp := MakeRequest(t, req, http.StatusOK)
+
+	var review api.PullReview
+	DecodeJSON(t, resp, &review)
+	assert.EqualValues(t, "COMMENT", review.State)
+
+	// verify the reply is threaded under the original review
+	comments, err := issues_model.FindComments(t.Context(), &issues_model.FindCommentsOptions{
+		ReviewID: originalComment.ReviewID,
+		Type:     issues_model.CommentTypeCode,
+	})
+	require.NoError(t, err)
+	assert.GreaterOrEqual(t, len(comments), 2)
+}
+
 func reviewsCountCheck(t *testing.T, name string, issueID, reviewerID int64, expectedDismissed, expectedRequested, expectedTotal int, expectApproval bool) {
 	t.Run(name, func(t *testing.T) {
 		unittest.AssertCountByCond(t, "review", builder.Eq{