Add the `inherited` field to Protected Branches

doc/api/protected_branches.md

@@ -83,7 +83,8 @@ Example response:
 ```
 
 Users on GitLab Premium or higher also see
-the `user_id` and `group_id` parameters:
+the `user_id`, `group_id` and `inherited` parameters. If the `inherited` parameter
+exists, means the setting was inherited from the project's group.
 
 Example response:
 
@@ -111,7 +112,8 @@ Example response:
       }
     ],
     "allow_force_push":false,
-    "code_owner_approval_required": false
+    "code_owner_approval_required": false,
+    "inherited": true
   },
   ...
 ]

ee/app/models/concerns/ee/protected_branch.rb

@@ -44,5 +44,10 @@ def supports_unprotection_restrictions?
 
       project.licensed_feature_available?(:unprotection_restrictions)
     end
+
+    def inherited?
+      !namespace_id.nil?
+    end
+    alias_method :inherited, :inherited?
   end
 end

ee/lib/ee/api/entities/protected_branch.rb

@@ -9,6 +9,7 @@ module ProtectedBranch
         prepended do
           expose :unprotect_access_levels, using: ::API::Entities::ProtectedRefAccess, documentation: { is_array: true }
           expose :code_owner_approval_required, documentation: { type: 'boolean' }
+          expose :inherited, documentation: { type: 'boolean' }
         end
       end
     end

ee/spec/models/ee/protected_branch_spec.rb

@@ -258,4 +258,22 @@
       end
     end
   end
+
+  describe '#inherited?' do
+    context 'when the `namespace_id` is nil' do
+      before do
+        subject.assign_attributes(namespace_id: nil)
+      end
+
+      it { is_expected.not_to be_inherited }
+    end
+
+    context 'when the `namespace_id` is present' do
+      before do
+        subject.assign_attributes(namespace_id: 123)
+      end
+
+      it { is_expected.to be_inherited }
+    end
+  end
 end

ee/spec/requests/api/protected_branches_spec.rb

@@ -21,6 +21,7 @@
 
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['unprotect_access_levels']).to eq([])
+        expect(json_response).to include('inherited')
       end
 
       context 'with per user/group access levels' do