Expose epicsCount under epic board lists

- Add tests
- Slight refactor to use current_user method in type
- Move some logic into BasicItemsListService

app/graphql/types/board_list_type.rb

@@ -8,6 +8,8 @@ module Types
     graphql_name 'BoardList'
     description 'Represents a list for an issue board'
 
+    alias_method :list, :object
+
     field :id, GraphQL::ID_TYPE, null: false,
           description: 'ID (global ID) of the list.'
     field :title, GraphQL::STRING_TYPE, null: false,
@@ -37,12 +39,10 @@ module Types
 
     def metadata
       strong_memoize(:metadata) do
-        list = self.object
-        user = context[:current_user]
         params = (context[:issue_filters] || {}).merge(board_id: list.board_id, id: list.id)
 
         ::Boards::Issues::ListService
-          .new(list.board.resource_parent, user, params)
+          .new(list.board.resource_parent, current_user, params)
           .metadata
       end
     end

app/services/boards/base_items_list_service.rb

@@ -11,8 +11,24 @@ module Boards
       ordered_items
     end
 
+    # rubocop: disable CodeReuse/ActiveRecord
+    def metadata
+      issues = item_model.arel_table
+      keys = metadata_fields.keys
+      # TODO: eliminate need for SQL literal fragment
+      columns = Arel.sql(metadata_fields.values_at(*keys).join(', '))
+      results = item_model.where(id: items.select(issues[:id])).pluck(columns)
+
+      Hash[keys.zip(results.flatten)]
+    end
+    # rubocop: enable CodeReuse/ActiveRecord
+
     private
 
+    def metadata_fields
+      { size: 'COUNT(*)' }
+    end
+
     def ordered_items
       raise NotImplementedError
     end

app/services/boards/issues/list_service.rb

@@ -35,10 +35,6 @@ module Boards
         @board ||= parent.boards.find(params[:board_id])
       end
 
-      def metadata_fields
-        { size: 'COUNT(*)' }
-      end
-
       def filter_params
         set_scope
         set_non_archived

doc/api/graphql/reference/index.md

@@ -1973,6 +1973,7 @@ Represents an epic board list.
 | ----- | ---- | ----------- |
 | `collapsed` | Boolean | Indicates if this list is collapsed for this user. |
 | `epics` | EpicConnection | List epics. |
+| `epicsCount` | Int | Count of epics in the list. |
 | `id` | BoardsEpicListID! | Global ID of the board list. |
 | `label` | Label | Label of the list. |
 | `listType` | String! | Type of the list. |

ee/app/graphql/types/boards/epic_list_type.rb

@@ -4,11 +4,15 @@ module Types
   module Boards
     # rubocop: disable Graphql/AuthorizeTypes
     class EpicListType < BaseObject
+      include Gitlab::Utils::StrongMemoize
+
       graphql_name 'EpicList'
       description 'Represents an epic board list'
 
       accepts ::Boards::EpicList
 
+      alias_method :list, :object
+
       field :id, type: ::Types::GlobalIDType[::Boards::EpicList], null: false,
             description: 'Global ID of the board list.'
 
@@ -31,9 +35,24 @@ module Types
             resolver: Resolvers::Boards::BoardListEpicsResolver,
             description: 'List epics.'
 
+      field :epics_count, GraphQL::INT_TYPE, null: true,
+            description: 'Count of epics in the list.'
+
       def collapsed
         object.collapsed?(current_user)
       end
+
+      def epics_count
+        metadata[:size]
+      end
+
+      def metadata
+        strong_memoize(:metadata) do
+          ::Boards::Epics::ListService
+              .new(list.epic_board.resource_parent, current_user, { board_id: list.epic_board_id, id: list.id })
+              .metadata
+        end
+      end
     end
     # rubocop: enable Graphql/AuthorizeTypes
   end

ee/spec/graphql/types/boards/epic_list_type_spec.rb

@@ -6,7 +6,7 @@ RSpec.describe GitlabSchema.types['EpicList'] do
   specify { expect(described_class.graphql_name).to eq('EpicList') }
 
   it 'has specific fields' do
-    expected_fields = %w[id title list_type position label epics collapsed]
+    expected_fields = %w[id title list_type position label epics epics_count collapsed]
 
     expect(described_class).to include_graphql_fields(*expected_fields)
   end

ee/spec/requests/api/graphql/boards/epic_lists_query_spec.rb

@@ -12,6 +12,8 @@ RSpec.describe 'get list of epic boards' do
   let_it_be(:list2) { create(:epic_list, epic_board: board, list_type: :closed) }
   let_it_be(:list3) { create(:epic_list, epic_board: board, list_type: :backlog) }
 
+  let_it_be(:some_epics) { create_list(:epic, 2, group: group) }
+
   def pagination_query(params = {})
     graphql_query_for(:group, { full_path: group.full_path },
       <<~BOARDS
@@ -78,6 +80,13 @@ RSpec.describe 'get list of epic boards' do
         assert_field_value('id', [global_id_of(list3), global_id_of(list1), global_id_of(list2)])
         assert_field_value('collapsed', [false, true, false])
       end
+
+      it 'returns the correct values for count' do
+        post_graphql(pagination_query, current_user: current_user)
+
+        assert_field_value('epicsCount', [2, 0, 0])
+      end
+    end
     end
   end