Allow the status of a rebase to be determined

doc/api/merge_requests.md

@@ -408,6 +408,7 @@ Parameters:
 - `merge_request_iid` (required) - The internal ID of the merge request
 - `render_html` (optional) - If `true` response includes rendered HTML for title and description
 - `include_diverged_commits_count` (optional) - If `true` response includes the commits behind the target branch
+- `include_rebase_in_progress` (optional) - If `true` response includes whether a rebase operation is in progress
 
 ```json
 {
@@ -461,6 +462,7 @@ Parameters:
   },
   "merge_when_pipeline_succeeds": true,
   "merge_status": "can_be_merged",
+  "merge_error": null,
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
@@ -505,7 +507,8 @@ Parameters:
     "head_sha": "2be7ddb704c7b6b83732fdd5b9f09d5a397b5f8f",
     "start_sha": "c380d3acebd181f13629a25d2e2acca46ffe1e00"
   },
-  "diverged_commits_count": 2
+  "diverged_commits_count": 2,
+  "rebase_in_progress": false
 }
 ```
 
@@ -773,6 +776,7 @@ POST /projects/:id/merge_requests
   },
   "merge_when_pipeline_succeeds": true,
   "merge_status": "can_be_merged",
+  "merge_error": null,
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
@@ -900,6 +904,7 @@ Must include at least one non-required attribute from above.
   },
   "merge_when_pipeline_succeeds": true,
   "merge_status": "can_be_merged",
+  "merge_error": null,
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
@@ -1043,6 +1048,7 @@ Parameters:
   },
   "merge_when_pipeline_succeeds": true,
   "merge_status": "can_be_merged",
+  "merge_error": null,
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
@@ -1158,6 +1164,7 @@ Parameters:
   },
   "merge_when_pipeline_succeeds": false,
   "merge_status": "can_be_merged",
+  "merge_error": null,
   "sha": "8888888888888888888888888888888888888888",
   "merge_commit_sha": null,
   "user_notes_count": 1,
@@ -1228,8 +1235,39 @@ curl --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/a
 ```
 
 This is an asynchronous request. The API will return an empty `202 Accepted`
-response if the request is enqueued successfully. You should poll the
-[Get single MR](#get-single-mr) endpoint to determine success or failure.
+response if the request is enqueued successfully.
+
+You can poll the [Get single MR](#get-single-mr) endpoint with the
+`include_rebase_in_progress` parameter to check the status of the
+asynchronous request.
+
+If the rebase operation is ongoing, the response will include the following:
+
+```json
+{
+  "rebase_in_progress": true
+  "merge_error": null
+}
+```
+
+Once the rebase operation has completed successfully, the response will include
+the following:
+
+```json
+{
+  "rebase_in_progress": false,
+  "merge_error": null,
+}
+```
+
+If the rebase operation fails, the response will include the following:
+
+```json
+{
+  "rebase_in_progress": false,
+  "merge_error": "Rebase failed. Please rebase locally",
+}
+```
 
 ## Comments on merge requests
 

lib/api/entities.rb

@@ -710,6 +710,10 @@ module API
 
       expose :diff_refs, using: Entities::DiffRefs
 
+      # Allow the status of a rebase to be determined
+      expose :merge_error
+      expose :rebase_in_progress?, as: :rebase_in_progress, if: -> (_, options) { options[:include_rebase_in_progress] }
+
       expose :diverged_commits_count, as: :diverged_commits_count, if: -> (_, options) { options[:include_diverged_commits_count] }
 
       def build_available?(options)

lib/api/merge_requests.rb

@@ -252,6 +252,7 @@ module API
         requires :merge_request_iid, type: Integer, desc: 'The IID of a merge request'
         optional :render_html, type: Boolean, desc: 'Returns the description and title rendered HTML'
         optional :include_diverged_commits_count, type: Boolean, desc: 'Returns the commits count behind the target branch'
+        optional :include_rebase_in_progress, type: Boolean, desc: 'Returns whether a rebase operation is ongoing '
       end
       desc 'Get a single merge request' do
         success Entities::MergeRequest
@@ -259,7 +260,13 @@ module API
       get ':id/merge_requests/:merge_request_iid' do
         merge_request = find_merge_request_with_access(params[:merge_request_iid])
 
-        present merge_request, with: Entities::MergeRequest, current_user: current_user, project: user_project, render_html: params[:render_html], include_diverged_commits_count: params[:include_diverged_commits_count]
+        present merge_request,
+          with: Entities::MergeRequest,
+          current_user: current_user,
+          project: user_project,
+          render_html: params[:render_html],
+          include_diverged_commits_count: params[:include_diverged_commits_count],
+          include_rebase_in_progress: params[:include_rebase_in_progress]
       end
 
       desc 'Get the participants of a merge request' do

spec/requests/api/merge_requests_spec.rb

@@ -359,6 +359,8 @@ describe API::MergeRequests do
       expect(json_response['should_close_merge_request']).to be_falsy
       expect(json_response['force_close_merge_request']).to be_falsy
       expect(json_response['changes_count']).to eq(merge_request.merge_request_diff.real_size)
+      expect(json_response['merge_error']).to eq(merge_request.merge_error)
+      expect(json_response).not_to include('rebase_in_progress')
     end
 
     it 'exposes description and title html when render_html is true' do
@@ -369,6 +371,14 @@ describe API::MergeRequests do
       expect(json_response).to include('title_html', 'description_html')
     end
 
+    it 'exposes rebase_in_progress when include_rebase_in_progress is true' do
+      get api("/projects/#{project.id}/merge_requests/#{merge_request.iid}", user), include_rebase_in_progress: true
+
+      expect(response).to have_gitlab_http_status(200)
+
+      expect(json_response).to include('rebase_in_progress')
+    end
+
     context 'merge_request_metrics' do
       before do
         merge_request.metrics.update!(merged_by: user,
@@ -1182,7 +1192,7 @@ describe API::MergeRequests do
   end
 
   describe 'PUT :id/merge_requests/:merge_request_iid/rebase' do
-    it 'enques a rebase of the merge request against the target branch' do
+    it 'enqueues a rebase of the merge request against the target branch' do
       Sidekiq::Testing.fake! do
         put api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/rebase", user)
       end