API: get participants from merge_requests & issues

changelogs/unreleased/issues-40986-get-participants-from-issues-mr-api.yml

+---
+title: 'API: get participants from merge_requests & issues'
+merge_request: 16187
+author: Brent Greeff
+type: added

doc/api/issues.md

@@ -1124,6 +1124,45 @@ Example response:
 ```
 
 
+## Participants on issues
+
+```
+GET /projects/:id/issues/:issue_iid/participants
+```
+
+| Attribute   | Type    | Required | Description                          |
+|-------------|---------|----------|--------------------------------------|
+| `id`        | integer/string | yes      | The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user  |
+| `issue_iid` | integer | yes      | The internal ID of a project's issue |
+
+```bash
+curl --request GET --header "PRIVATE-TOKEN: 9koXpg98eAheJpvBs5tK" https://gitlab.example.com/api/v4/projects/5/issues/93/participants
+```
+
+Example response:
+
+```json
+[
+  {
+    "id": 1,
+    "name": "John Doe1",
+    "username": "user1",
+    "state": "active",
+    "avatar_url": "http://www.gravatar.com/avatar/c922747a93b40d1ea88262bf1aebee62?s=80&d=identicon",
+    "web_url": "http://localhost/user1"
+  },
+  {
+    "id": 5,
+    "name": "John Doe5",
+    "username": "user5",
+    "state": "active",
+    "avatar_url": "http://www.gravatar.com/avatar/4aea8cf834ed91844a2da4ff7ae6b491?s=80&d=identicon",
+    "web_url": "http://localhost/user5"
+  }
+]
+```
+
+
 ## Comments on issues
 
 Comments are done via the [notes](notes.md) resource.

doc/api/merge_requests.md

@@ -308,6 +308,41 @@ Parameters:
 }
 ```
 
+## Get single MR participants
+
+Get a list of merge request participants.
+
+```
+GET /projects/:id/merge_requests/:merge_request_iid/participants
+```
+
+Parameters:
+
+- `id` (required) - The ID or [URL-encoded path of the project](README.md#namespaced-path-encoding) owned by the authenticated user
+- `merge_request_iid` (required) - The internal ID of the merge request
+
+
+```json
+[
+  {
+    "id": 1,
+    "name": "John Doe1",
+    "username": "user1",
+    "state": "active",
+    "avatar_url": "http://www.gravatar.com/avatar/c922747a93b40d1ea88262bf1aebee62?s=80&d=identicon",
+    "web_url": "http://localhost/user1"
+  },
+  {
+    "id": 2,
+    "name": "John Doe2",
+    "username": "user2",
+    "state": "active",
+    "avatar_url": "http://www.gravatar.com/avatar/10fc7f102be8de7657fb4d80898bbfe3?s=80&d=identicon",
+    "web_url": "http://localhost/user2"
+  },
+]
+```
+
 ## Get single MR commits
 
 Get a list of merge request commits.

lib/api/issues.rb

@@ -277,6 +277,19 @@ module API
         present paginate(merge_requests), with: Entities::MergeRequestBasic, current_user: current_user, project: user_project
       end
 
+      desc 'List participants for an issue'  do
+        success Entities::UserBasic
+      end
+      params do
+        requires :issue_iid, type: Integer, desc: 'The internal ID of a project issue'
+      end
+      get ':id/issues/:issue_iid/participants' do
+        issue = find_project_issue(params[:issue_iid])
+        participants = ::Kaminari.paginate_array(issue.participants)
+
+        present paginate(participants), with: Entities::UserBasic, current_user: current_user, project: user_project
+      end
+
       desc 'Get the user agent details for an issue' do
         success Entities::UserAgentDetail
       end

lib/api/merge_requests.rb

@@ -185,6 +185,16 @@ module API
         present merge_request, with: Entities::MergeRequest, current_user: current_user, project: user_project
       end
 
+      desc 'Get the participants of a merge request' do
+        success Entities::UserBasic
+      end
+      get ':id/merge_requests/:merge_request_iid/participants' do
+        merge_request = find_merge_request_with_access(params[:merge_request_iid])
+        participants = ::Kaminari.paginate_array(merge_request.participants)
+
+        present paginate(participants), with: Entities::UserBasic
+      end
+
       desc 'Get the commits of a merge request' do
         success Entities::Commit
       end

spec/requests/api/issues_spec.rb

@@ -1582,4 +1582,16 @@ describe API::Issues, :mailer do
     expect(json_response).to be_an Array
     expect(json_response.length).to eq(size) if size
   end
+
+  describe 'GET projects/:id/issues/:issue_iid/participants' do
+    it_behaves_like 'issuable participants endpoint' do
+      let(:entity) { issue }
+    end
+
+    it 'returns 404 if the issue is confidential' do
+      post api("/projects/#{project.id}/issues/#{confidential_issue.iid}/participants", non_member)
+
+      expect(response).to have_gitlab_http_status(404)
+    end
+  end
 end

spec/requests/api/merge_requests_spec.rb

@@ -500,6 +500,12 @@ describe API::MergeRequests do
     end
   end
 
+  describe 'GET /projects/:id/merge_requests/:merge_request_iid/participants' do
+    it_behaves_like 'issuable participants endpoint' do
+      let(:entity) { merge_request }
+    end
+  end
+
   describe 'GET /projects/:id/merge_requests/:merge_request_iid/commits' do
     it 'returns a 200 when merge request is valid' do
       get api("/projects/#{project.id}/merge_requests/#{merge_request.iid}/commits", user)

spec/support/shared_examples/requests/api/issuable_participants_examples.rb

+shared_examples 'issuable participants endpoint' do
+  let(:area) { entity.class.name.underscore.pluralize }
+
+  it 'returns participants' do
+    get api("/projects/#{project.id}/#{area}/#{entity.iid}/participants", user)
+
+    expect(response).to have_gitlab_http_status(200)
+    expect(response).to include_pagination_headers
+    expect(json_response).to be_an Array
+    expect(json_response.size).to eq(entity.participants.size)
+
+    last_participant = entity.participants.last
+    expect(json_response.last['id']).to eq(last_participant.id)
+    expect(json_response.last['name']).to eq(last_participant.name)
+    expect(json_response.last['username']).to eq(last_participant.username)
+  end
+
+  it 'returns a 404 when iid does not exist' do
+    get api("/projects/#{project.id}/#{area}/999/participants", user)
+
+    expect(response).to have_gitlab_http_status(404)
+  end
+
+  it 'returns a 404 when id is used instead of iid' do
+    get api("/projects/#{project.id}/#{area}/#{entity.id}/participants", user)
+
+    expect(response).to have_gitlab_http_status(404)
+  end
+end