Add `author_username` param to MR API

app/finders/merge_requests_finder.rb

@@ -14,6 +14,7 @@
 #     milestone_title: string
 #     release_tag: string
 #     author_id: integer
+#     author_username: string
 #     assignee_id: integer
 #     search: string
 #     in: 'title', 'description', or a string joining them with comma

changelogs/unreleased/ag-add-author-username-to-mr-api.yml

+---
+title: Accept `author_username` as a param in Merge Requests API
+merge_request: 28100
+author:
+type: changed

doc/api/merge_requests.md

@@ -30,6 +30,7 @@ GET /merge_requests?state=all
 GET /merge_requests?milestone=release
 GET /merge_requests?labels=bug,reproduced
 GET /merge_requests?author_id=5
+GET /merge_requests?author_username=gitlab-bot
 GET /merge_requests?my_reaction_emoji=star
 GET /merge_requests?scope=assigned_to_me
 GET /merge_requests?search=foo&in=title
@@ -51,7 +52,8 @@ Parameters:
 | `updated_after`                 | datetime       | no       | Return merge requests updated on or after the given time                                                               |
 | `updated_before`                | datetime       | no       | Return merge requests updated on or before the given time                                                              |
 | `scope`                         | string         | no       | Return merge requests for the given scope: `created_by_me`, `assigned_to_me` or `all`. Defaults to `created_by_me`<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead. |
-| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id`. Combine with `scope=all` or `scope=assigned_to_me`              |
+| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id`. Mutually exclusive with `author_username`. Combine with `scope=all` or `scope=assigned_to_me`
+| `author_username`               | string         | no       | Returns merge requests created by the given `username`. Mutually exclusive with `author_id`. _([Introduced][ce-13060] in GitLab 12.10)_             |           |
 | `assignee_id`                   | integer        | no       | Returns merge requests assigned to the given user `id`. `None` returns unassigned merge requests. `Any` returns merge requests with an assignee. |
 | `approver_ids` **(STARTER)**    | integer array  | no       | Returns merge requests which have specified all the users with the given `id`s as individual approvers. `None` returns merge requests without approvers. `Any` returns merge requests with an approver. |
 | `approved_by_ids` **(STARTER)** | integer array  | no       | Returns merge requests which have been approved by all the users with the given `id`s (Max: 5). `None` returns merge requests with no approvals. `Any` returns merge requests with an approval. |
@@ -230,7 +232,8 @@ Parameters:
 | `updated_after`                 | datetime       | no       | Return merge requests updated on or after the given time                                                                       |
 | `updated_before`                | datetime       | no       | Return merge requests updated on or before the given time                                                                      |
 | `scope`                         | string         | no       | Return merge requests for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br> For versions before 11.0, use the now deprecated `created-by-me` or `assigned-to-me` scopes instead.<br> _([Introduced][ce-13060] in GitLab 9.5. [Changed to snake_case][ce-18935] in GitLab 11.0)_ |
-| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id` _([Introduced][ce-13060] in GitLab 9.5)_                                 |
+| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id`. Mutually exclusive with `author_username`. _([Introduced][ce-13060] in GitLab 9.5)_
+| `author_username`               | string         | no       | Returns merge requests created by the given `username`. Mutually exclusive with `author_id`. _([Introduced][ce-13060] in GitLab 12.10)_             |     |
 | `assignee_id`                   | integer        | no       | Returns merge requests assigned to the given user `id`. `None` returns unassigned merge requests. `Any` returns merge requests with an assignee. _([Introduced][ce-13060] in GitLab 9.5)_ |
 | `approver_ids` **(STARTER)**    | integer array  | no       | Returns merge requests which have specified all the users with the given `id`s as individual approvers. `None` returns merge requests without approvers. `Any` returns merge requests with an approver. |
 | `approved_by_ids` **(STARTER)** | integer array  | no       | Returns merge requests which have been approved by all the users with the given `id`s (Max: 5). `None` returns merge requests with no approvals. `Any` returns merge requests with an approval. |
@@ -392,7 +395,8 @@ Parameters:
 | `updated_after`                 | datetime       | no       | Return merge requests updated on or after the given time                                                                       |
 | `updated_before`                | datetime       | no       | Return merge requests updated on or before the given time                                                                      |
 | `scope`                         | string         | no       | Return merge requests for the given scope: `created_by_me`, `assigned_to_me` or `all`.<br>                                     |
-| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id` _([Introduced][ce-13060] in GitLab 9.5)_                                 |
+| `author_id`                     | integer        | no       | Returns merge requests created by the given user `id`. Mutually exclusive with `author_username`. _([Introduced][ce-13060] in GitLab 9.5)_
+| `author_username`               | string         | no       | Returns merge requests created by the given `username`. Mutually exclusive with `author_id`. _([Introduced][ce-13060] in GitLab 12.10)_             |                              |
 | `assignee_id`                   | integer        | no       | Returns merge requests assigned to the given user `id`. `None` returns unassigned merge requests. `Any` returns merge requests with an assignee. _([Introduced][ce-13060] in GitLab 9.5)_ |
 | `approver_ids` **(STARTER)**    | integer array  | no       | Returns merge requests which have specified all the users with the given `id`s as individual approvers. `None` returns merge requests without approvers. `Any` returns merge requests with an approver. |
 | `approved_by_ids` **(STARTER)** | integer array  | no       | Returns merge requests which have been approved by all the users with the given `id`s (Max: 5). `None` returns merge requests with no approvals. `Any` returns merge requests with an approval. |

lib/api/helpers/merge_requests_helpers.rb

@@ -36,7 +36,11 @@ module API
                  type: String,
                  values: %w[simple],
                  desc: 'If simple, returns the `iid`, URL, title, description, and basic state of merge request'
+
         optional :author_id, type: Integer, desc: 'Return merge requests which are authored by the user with the given ID'
+        optional :author_username, type: String, desc: 'Return merge requests which are authored by the user with the given username'
+        mutually_exclusive :author_id, :author_username
+
         optional :assignee_id,
                  types: [Integer, String],
                  integer_none_any: true,

spec/requests/api/merge_requests_spec.rb

@@ -526,12 +526,48 @@ describe API::MergeRequests do
         expect_response_contain_exactly(merge_request3.id)
       end
 
-      it 'returns an array of merge requests authored by the given user' do
-        merge_request3 = create(:merge_request, :simple, author: user2, assignees: [user], source_project: project2, target_project: project2, source_branch: 'other-branch')
+      context 'filter by author' do
+        let(:user3) { create(:user) }
+        let(:project) { create(:project, :public, :repository, creator: user3, namespace: user3.namespace, only_allow_merge_if_pipeline_succeeds: false) }
+        let!(:merge_request3) do
+          create(:merge_request, :simple, author: user3, assignees: [user3], source_project: project, target_project: project, source_branch: 'other-branch')
+        end
 
-        get api('/merge_requests', user), params: { author_id: user2.id, scope: :all }
+        context 'when only `author_id` is passed' do
+          it 'returns an array of merge requests authored by the given user' do
+            get api('/merge_requests', user), params: {
+              author_id: user3.id,
+              scope: :all
+            }
 
-        expect_response_contain_exactly(merge_request3.id)
+            expect_response_contain_exactly(merge_request3.id)
+          end
+        end
+
+        context 'when only `author_username` is passed' do
+          it 'returns an array of merge requests authored by the given user(by `author_username`)' do
+            get api('/merge_requests', user), params: {
+              author_username: user3.username,
+              scope: :all
+            }
+
+            expect_response_contain_exactly(merge_request3.id)
+          end
+        end
+
+        context 'when both `author_id` and `author_username` are passed' do
+          it 'returns a 400' do
+            get api('/merge_requests', user), params: {
+              author_id: user.id,
+              author_username: user2.username,
+              scope: :all
+            }
+
+            expect(response).to have_gitlab_http_status(:bad_request)
+            expect(json_response['error']).to eq(
+              'author_id, author_username are mutually exclusive')
+          end
+        end
       end
 
       it 'returns an array of merge requests assigned to the given user' do