Add API endpoint to reply to pull request review comments (#36683)

Adds a dedicated endpoint for replying to pull request review comments,

```
POST /repos/{owner}/{repo}/pulls/{index}/comments/{id}/replies
{ "body": "..." }
```

The reply is threaded under the same review as the parent comment.

Ref: https://gitea.com/gitea/gitea-mcp/issues/129
Fixes: https://github.com/go-gitea/gitea/issues/37419
Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>
Co-authored-by: Nicolas <bircni@icloud.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/structs/pull_review.go

@@ -94,6 +94,11 @@ type CreatePullReviewComment struct {
 	NewLineNum int64 `json:"new_position"`
 }
 
+// CreatePullReviewCommentReplyOptions are options to reply to a pull request review comment
+type CreatePullReviewCommentReplyOptions struct {
+	Body string `json:"body" binding:"Required"`
+}
+
 // SubmitPullReviewOptions are options to submit a pending pull request review
 type SubmitPullReviewOptions struct {
 	Event ReviewStateType `json:"event"`

routers/api/v1/api.go

@@ -1369,6 +1369,7 @@ func Routes() *web.Router {
 						m.Combo("/requested_reviewers", reqToken()).
 							Delete(bind(api.PullReviewRequestOptions{}), repo.DeleteReviewRequests).
 							Post(bind(api.PullReviewRequestOptions{}), repo.CreateReviewRequests)
+						m.Post("/comments/{id}/replies", reqToken(), mustNotBeArchived, bind(api.CreatePullReviewCommentReplyOptions{}), repo.CreatePullReviewCommentReply)
 					})
 					m.Get("/{base}/*", repo.GetPullRequestByBaseHead)
 				}, mustAllowPulls, reqRepoReader(unit.TypeCode), context.ReferencesGitRepo())

routers/api/v1/repo/pull_review.go

@@ -208,6 +208,88 @@ func GetPullReviewComments(ctx *context.APIContext) {
 	ctx.JSON(http.StatusOK, apiComments)
 }
 
+// CreatePullReviewCommentReply replies to a pull request review comment.
+// The URL mirrors GitHub's endpoint, {index} is verified against the parent comment's pull request.
+func CreatePullReviewCommentReply(ctx *context.APIContext) {
+	// swagger:operation POST /repos/{owner}/{repo}/pulls/{index}/comments/{id}/replies repository repoCreatePullReviewCommentReply
+	// ---
+	// summary: Reply to a pull request review comment
+	// consumes:
+	// - application/json
+	// produces:
+	// - application/json
+	// parameters:
+	// - name: owner
+	//   in: path
+	//   description: owner of the repo
+	//   type: string
+	//   required: true
+	// - name: repo
+	//   in: path
+	//   description: name of the repo
+	//   type: string
+	//   required: true
+	// - name: index
+	//   in: path
+	//   description: index of the pull request
+	//   type: integer
+	//   format: int64
+	//   required: true
+	// - name: id
+	//   in: path
+	//   description: id of the review comment to reply to
+	//   type: integer
+	//   format: int64
+	//   required: true
+	// - name: body
+	//   in: body
+	//   required: true
+	//   schema:
+	//     "$ref": "#/definitions/CreatePullReviewCommentReplyOptions"
+	// responses:
+	//   "201":
+	//     "$ref": "#/responses/PullReviewComment"
+	//   "400":
+	//     "$ref": "#/responses/validationError"
+	//   "404":
+	//     "$ref": "#/responses/notFound"
+	//   "422":
+	//     "$ref": "#/responses/validationError"
+
+	opts := web.GetForm(ctx).(*api.CreatePullReviewCommentReplyOptions)
+
+	parent := getPullReviewCommentToResolve(ctx)
+	if parent == nil {
+		return
+	}
+	if parent.Issue.Index != ctx.PathParamInt64("index") {
+		ctx.APIErrorNotFound()
+		return
+	}
+	if parent.ReviewID == 0 {
+		ctx.APIError(http.StatusBadRequest, "comment is not a review comment")
+		return
+	}
+
+	comment, err := pull_service.CreateCodeComment(ctx,
+		ctx.Doer, ctx.Repo.GitRepo, parent.Issue,
+		parent.Line, opts.Body, parent.TreePath,
+		false, parent.ReviewID,
+		"", nil,
+	)
+	if err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	if err := comment.LoadPoster(ctx); err != nil {
+		ctx.APIErrorInternal(err)
+		return
+	}
+	comment.Issue = parent.Issue
+
+	ctx.JSON(http.StatusCreated, convert.ToPullReviewComment(ctx, comment, ctx.Doer))
+}
+
 // ResolvePullReviewComment resolves a review comment in a pull request
 func ResolvePullReviewComment(ctx *context.APIContext) {
 	// swagger:operation POST /repos/{owner}/{repo}/pulls/comments/{id}/resolve repository repoResolvePullReviewComment

routers/api/v1/swagger/options.go

@@ -168,6 +168,9 @@ type swaggerParameterBodies struct {
 	// in:body
 	CreatePullReviewComment api.CreatePullReviewComment
 
+	// in:body
+	CreatePullReviewCommentReplyOptions api.CreatePullReviewCommentReplyOptions
+
 	// in:body
 	SubmitPullReviewOptions api.SubmitPullReviewOptions
 

templates/swagger/v1_json.tmpl

@@ -14470,6 +14470,75 @@
         }
       }
     },
+    "/repos/{owner}/{repo}/pulls/{index}/comments/{id}/replies": {
+      "post": {
+        "consumes": [
+          "application/json"
+        ],
+        "produces": [
+          "application/json"
+        ],
+        "tags": [
+          "repository"
+        ],
+        "summary": "Reply to a pull request review comment",
+        "operationId": "repoCreatePullReviewCommentReply",
+        "parameters": [
+          {
+            "type": "string",
+            "description": "owner of the repo",
+            "name": "owner",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "string",
+            "description": "name of the repo",
+            "name": "repo",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "integer",
+            "format": "int64",
+            "description": "index of the pull request",
+            "name": "index",
+            "in": "path",
+            "required": true
+          },
+          {
+            "type": "integer",
+            "format": "int64",
+            "description": "id of the review comment to reply to",
+            "name": "id",
+            "in": "path",
+            "required": true
+          },
+          {
+            "name": "body",
+            "in": "body",
+            "required": true,
+            "schema": {
+              "$ref": "#/definitions/CreatePullReviewCommentReplyOptions"
+            }
+          }
+        ],
+        "responses": {
+          "201": {
+            "$ref": "#/responses/PullReviewComment"
+          },
+          "400": {
+            "$ref": "#/responses/validationError"
+          },
+          "404": {
+            "$ref": "#/responses/notFound"
+          },
+          "422": {
+            "$ref": "#/responses/validationError"
+          }
+        }
+      }
+    },
     "/repos/{owner}/{repo}/pulls/{index}/commits": {
       "get": {
         "produces": [
@@ -24088,6 +24157,17 @@
       },
       "x-go-package": "code.gitea.io/gitea/modules/structs"
     },
+    "CreatePullReviewCommentReplyOptions": {
+      "description": "CreatePullReviewCommentReplyOptions are options to reply to a pull request review comment",
+      "type": "object",
+      "properties": {
+        "body": {
+          "type": "string",
+          "x-go-name": "Body"
+        }
+      },
+      "x-go-package": "code.gitea.io/gitea/modules/structs"
+    },
     "CreatePullReviewOptions": {
       "description": "CreatePullReviewOptions are options to create a pull request review",
       "type": "object",

tests/integration/api_pull_review_test.go

@@ -29,6 +29,11 @@ import (
 
 func TestAPIPullReview(t *testing.T) {
 	defer tests.PrepareTestEnv(t)()
+	t.Run("General", testAPIPullReviewGeneral)
+	t.Run("CommentReply", testAPIPullReviewCommentReply)
+}
+
+func testAPIPullReviewGeneral(t *testing.T) {
 	pullIssue := unittest.AssertExistsAndLoadBean(t, &issues_model.Issue{ID: 3})
 	assert.NoError(t, pullIssue.LoadAttributes(t.Context()))
 	repo := unittest.AssertExistsAndLoadBean(t, &repo_model.Repository{ID: pullIssue.RepoID})
@@ -526,6 +531,55 @@ func TestAPIPullReviewStayDismissed(t *testing.T) {
 		pullIssue.ID, user8.ID, 2, 0, 3, false)
 }
 
+func testAPIPullReviewCommentReply(t *testing.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)
+
+	parent, err := pull_service.CreateCodeComment(t.Context(), doer, gitRepo, pullIssue, 1, "parent comment", "README.md", false, 0, commitID, nil)
+	require.NoError(t, err)
+	require.NotZero(t, parent.ReviewID)
+
+	repo := pullIssue.Repo
+	session := loginUser(t, doer.Name)
+	token := getTokenForLoggedInUser(t, session, auth_model.AccessTokenScopeWriteRepository)
+
+	url := fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/comments/%d/replies", repo.OwnerName, repo.Name, pullIssue.Index, parent.ID)
+
+	// happy path
+	req := NewRequestWithJSON(t, http.MethodPost, url, &api.CreatePullReviewCommentReplyOptions{Body: "the reply"}).AddTokenAuth(token)
+	resp := MakeRequest(t, req, http.StatusCreated)
+
+	var reply api.PullReviewComment
+	DecodeJSON(t, resp, &reply)
+	assert.Equal(t, "the reply", reply.Body)
+	assert.Equal(t, parent.ReviewID, reply.ReviewID)
+	assert.Equal(t, "README.md", reply.Path)
+
+	// empty body — caught by binding
+	req = NewRequestWithJSON(t, http.MethodPost, url, &api.CreatePullReviewCommentReplyOptions{}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusUnprocessableEntity)
+
+	// reply to a non-existent comment
+	bad := fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/comments/%d/replies", repo.OwnerName, repo.Name, pullIssue.Index, 999999)
+	req = NewRequestWithJSON(t, http.MethodPost, bad, &api.CreatePullReviewCommentReplyOptions{Body: "x"}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusNotFound)
+
+	// reply to a code comment that belongs to a different PR — 404
+	otherCodeComment := unittest.AssertExistsAndLoadBean(t, &issues_model.Comment{ID: 4, Type: issues_model.CommentTypeCode})
+	require.NotEqual(t, pullIssue.ID, otherCodeComment.IssueID)
+	wrongPR := fmt.Sprintf("/api/v1/repos/%s/%s/pulls/%d/comments/%d/replies", repo.OwnerName, repo.Name, pullIssue.Index, otherCodeComment.ID)
+	req = NewRequestWithJSON(t, http.MethodPost, wrongPR, &api.CreatePullReviewCommentReplyOptions{Body: "x"}).AddTokenAuth(token)
+	MakeRequest(t, req, http.StatusNotFound)
+}
+
 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{