POST instead of DELETE to unapprove an MR through the API

doc/api/merge_requests.md

@@ -640,6 +640,24 @@ POST /projects/:id/merge_requests/:merge_request_iid/approve
 }
 ```
 
+## Unapprove Merge Request
+
+>**Note:** This API endpoint is only available on 9.0 EE and above.
+
+If you did approve a merge request, you can unapprove it using the following
+endpoint:
+
+```
+POST /projects/:id/merge_requests/:merge_request_iid/unapprove
+```
+
+**Parameters:**
+
+| Attribute           | Type    | Required | Description         |
+|---------------------|---------|----------|---------------------|
+| `id`                | integer | yes      | The ID of a project |
+| `merge_request_iid` | integer | yes      | The IID of MR       |
+
 ## Cancel Merge When Pipeline Succeeds
 
 If you don't have permissions to accept this merge request - you'll get a `401`

doc/api/v3_to_v4.md

@@ -87,3 +87,4 @@ Below are the changes made between V3 and V4.
 - Remove the ProjectGitHook API. Use the ProjectPushRule API instead [!1301](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1301)
 - Removed `repository_storage` from `PUT /application/settings` and `GET /application/settings` (use `repository_storages` instead) [!1307](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1307)
 - Removed `elasticsearch_host` and `elasticsearch_port` from `PUT /application/settings` (use `elasticsearch_url` instead) [!1305](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1305)
+- Make approval API more RESTful. Use `POST /projects/:id/merge_requests/:merge_request_iid/unapprove` to unapprove a merge request. [!1518](https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1518)

lib/api/merge_requests.rb

@@ -279,7 +279,7 @@ module API
         present merge_request, with: Entities::MergeRequestApprovals, current_user: current_user
       end
 
-      delete ':id/merge_requests/:merge_request_iid/unapprove' do
+      post ':id/merge_requests/:merge_request_iid/unapprove' do
         merge_request = find_project_merge_request(params[:merge_request_iid])
 
         not_found! unless merge_request.has_approved?(current_user)

spec/requests/api/merge_requests_spec.rb

@@ -887,7 +887,7 @@ describe API::MergeRequests, api: true  do
     end
   end
 
-  describe 'DELETE :id/merge_requests/:merge_request_iid/unapprove' do
+  describe 'POST :id/merge_requests/:merge_request_iid/unapprove' do
     before { project.update_attribute(:approvals_before_merge, 2) }
 
     context 'as a user who has approved the merge request' do
@@ -901,11 +901,11 @@ describe API::MergeRequests, api: true  do
         merge_request.approvals.create(user: approver)
         merge_request.approvals.create(user: unapprover)
 
-        delete api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/unapprove", unapprover)
+        post api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/unapprove", unapprover)
       end
 
       it 'unapproves the merge request' do
-        expect(response.status).to eq(200)
+        expect(response.status).to eq(201)
         expect(json_response['approvals_left']).to eq(1)
         usernames = json_response['approved_by'].map { |u| u['user']['username'] }
         expect(usernames).not_to include(unapprover.username)