Fix boards API with special milestones

ee/lib/ee/api/entities.rb

@@ -93,17 +93,22 @@ module EE
         extend ActiveSupport::Concern
 
         prepended do
-          def scoped_issue_available?(board)
-            board.parent.feature_available?(:scoped_issue_board)
-          end
-
           # Default filtering configuration
           expose :name
           expose :group
-          expose :milestone, using: ::API::Entities::Milestone, if: ->(board, _) { scoped_issue_available?(board) }
-          expose :assignee, using: ::API::Entities::UserBasic, if: ->(board, _) { scoped_issue_available?(board) }
-          expose :labels, using: ::API::Entities::LabelBasic, if: ->(board, _) { scoped_issue_available?(board) }
-          expose :weight, if: ->(board, _) { scoped_issue_available?(board) }
+
+          with_options if: ->(board, _) { board.parent.feature_available?(:scoped_issue_board) } do
+            expose :milestone do |board|
+              if board.milestone.is_a?(Milestone)
+                ::API::Entities::Milestone.represent(board.milestone)
+              else
+                SpecialBoardFilter.represent(board.milestone)
+              end
+            end
+            expose :assignee, using: ::API::Entities::UserBasic
+            expose :labels, using: ::API::Entities::LabelBasic
+            expose :weight
+          end
         end
       end
 
@@ -213,6 +218,10 @@ module EE
         expose :target, as: :target_issue, using: ::API::Entities::IssueBasic
       end
 
+      class SpecialBoardFilter < Grape::Entity
+        expose :title
+      end
+
       class Approvals < Grape::Entity
         expose :user, using: ::API::Entities::UserBasic
       end

ee/spec/requests/api/boards_spec.rb

@@ -14,4 +14,24 @@ describe API::Boards do
     it_behaves_like 'milestone board list'
     it_behaves_like 'assignee board list'
   end
+
+  context 'GET /projects/:id/boards/:board_id with special milestones' do
+    let(:url) { "/projects/#{board_parent.id}/boards/#{board.id}" }
+
+    it 'returns board with Upcoming milestone' do
+      board.update(milestone_id: Milestone::Upcoming.id)
+
+      get api(url, user)
+
+      expect(json_response["milestone"]["title"]).to eq(Milestone::Upcoming.title)
+    end
+
+    it 'returns board with Started milestone' do
+      board.update(milestone_id: Milestone::Started.id)
+
+      get api(url, user)
+
+      expect(json_response["milestone"]["title"]).to eq(Milestone::Started.title)
+    end
+  end
 end