ProtectedBranch API includes user_id/group_id in access levels

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/4152

changelogs/unreleased-ee/jej-protected-branch-api-includes-user-ids.yml

+---
+title: EE Protected Branches API access levels include user_id/group_id where relevant
+merge_request: 3535
+author:
+type: changed

doc/api/protected_branches.md

@@ -36,13 +36,17 @@ Example response:
     "push_access_levels": [
       {
         "access_level": 40,
+        "user_id": null,
+        "group_id": null,
         "access_level_description": "Masters"
       }
     ],
     "merge_access_levels": [
       {
-        "access_level": 40,
-        "access_level_description": "Masters"
+        "access_level": null,
+        "user_id": null,
+        "group_id": 1234,
+        "access_level_description": "Example Merge Group"
       }
     ]
   },
@@ -75,13 +79,17 @@ Example response:
   "push_access_levels": [
     {
       "access_level": 40,
+      "user_id": null,
+      "group_id": null,
       "access_level_description": "Masters"
     }
   ],
   "merge_access_levels": [
     {
-      "access_level": 40,
-      "access_level_description": "Masters"
+      "access_level": null,
+      "user_id": null,
+      "group_id": 1234,
+      "access_level_description": "Example Merge Group"
     }
   ]
 }
@@ -115,12 +123,16 @@ Example response:
   "push_access_levels": [
     {
       "access_level": 30,
+      "user_id": null,
+      "group_id": null,
       "access_level_description": "Developers + Masters"
     }
   ],
   "merge_access_levels": [
     {
       "access_level": 30,
+      "user_id": null,
+      "group_id": null,
       "access_level_description": "Developers + Masters"
     }
   ]

lib/api/entities.rb

@@ -337,6 +337,12 @@ module API
 
     class ProtectedRefAccess < Grape::Entity
       expose :access_level
+
+      ## EE-only
+      expose :user_id
+      expose :group_id
+      ## EE-only
+
       expose :access_level_description do |protected_ref_access|
         protected_ref_access.humanize
       end

spec/requests/api/protected_branches_spec.rb

@@ -66,6 +66,27 @@ describe API::ProtectedBranches do
           let(:message) { '404 Not found' }
         end
       end
+
+      context 'with per user/group access levels' do
+        let(:push_user) { create(:user) }
+        let(:merge_group) { create(:group) }
+
+        before do
+          protected_branch.push_access_levels.create!(user: push_user)
+          protected_branch.merge_access_levels.create!(group: merge_group)
+        end
+
+        it 'returns access level details' do
+          get api(route, user)
+
+          push_user_ids = json_response['push_access_levels'].map {|level| level['user_id']}
+          merge_group_ids = json_response['merge_access_levels'].map {|level| level['group_id']}
+
+          expect(response).to have_gitlab_http_status(200)
+          expect(push_user_ids).to include(push_user.id)
+          expect(merge_group_ids).to include(merge_group.id)
+        end
+      end
     end
 
     context 'when authenticated as a master' do