Expose epic groupings in boards

Added a new epic field to the board type.

ee/app/finders/epics_finder.rb

@@ -30,6 +30,7 @@ class EpicsFinder < IssuableFinder
 
   def self.scalar_params
     @scalar_params ||= %i[
+      board
       parent_id
       author_id
       author_username
@@ -108,6 +109,7 @@ class EpicsFinder < IssuableFinder
   end
 
   def filter_items(items)
+    items = in_board(items)
     items = by_created_at(items)
     items = by_updated_at(items)
     items = by_author(items)
@@ -154,6 +156,16 @@ class EpicsFinder < IssuableFinder
     items.iid_starts_with(query)
   end
 
+  def in_board(items)
+    board = params[:board]
+    return items unless board.present?
+
+    list_service = Boards::Issues::ListService.new(board.resource_parent, current_user, { board_id: board.id })
+    issues = list_service.execute.except(:order).pluck_primary_key
+    epics_in_boards = EpicIssue.where(issue: issues)
+    items.id_in(epics_in_boards.select("epic_id as id"))
+  end
+
   def related_groups
     include_ancestors = params.fetch(:include_ancestor_groups, false)
     include_descendants = params.fetch(:include_descendant_groups, true)

ee/app/graphql/ee/types/board_type.rb

@@ -20,6 +20,10 @@ module EE
 
         field :weight, type: GraphQL::INT_TYPE, null: true,
               description: 'Weight of the board.'
+
+        field :epic_groups, ::Types::EpicType.connection_type, null: true,
+              description: 'Epics associated with board issues.',
+              resolver: ::Resolvers::BoardGroupings::EpicsResolver
       end
     end
   end

ee/app/graphql/resolvers/board_groupings/epics_resolver.rb

+# frozen_string_literal: true
+
+module Resolvers
+  module BoardGroupings
+    class EpicsResolver < BaseResolver
+
+     type Types::EpicType, null: true
+
+      def resolve(**args)
+        board = object.respond_to?(:sync) ? object.sync : object
+
+        return [] unless resolver_object.present?
+        return [] unless epic_feature_enabled?
+
+        EpicsFinder.new(context[:current_user], args.merge(board: board)).execute
+      end
+
+      private
+
+      attr_reader :resolver_object
+
+      def epic_feature_enabled?
+        group.feature_available?(:epics)
+      end
+    end
+  end
+end

ee/spec/finders/epics_finder_spec.rb

@@ -459,6 +459,26 @@ RSpec.describe EpicsFinder do
           end
         end
 
+        context 'by issue board' do
+          let_it_be(:epic1) { create(:epic, group: group, title: "first epic") }
+          let_it_be(:epic2) { create(:epic, group: group, title: "second epic") }
+          let_it_be(:label) { create(:group_label, group: group, name: 'some label') }
+          let_it_be(:project) { create(:project, namespace: group) }
+          let_it_be(:board) { create(:board, group: group) }
+          let_it_be(:label_list) { create(:list, board: board, label: label) }
+          let_it_be(:backlog_list) { create(:backlog_list, board: board) }
+          let_it_be(:issue) { create(:labeled_issue, project: project, labels: [label]) }
+          let_it_be(:epic_issue) { create(:epic_issue, epic: epic1, issue: issue) }
+
+          it 'returns epics that are in the board' do
+            params = {
+                board_id: board.id
+            }
+
+            expect(epics(params)).to contain_exactly(epic1)
+          end
+        end
+
         context 'when using group cte for search' do
           context 'and two labels more search string are present' do
             let_it_be(:label1) { create(:label) }

ee/spec/graphql/ee/types/board_type_spec.rb

@@ -4,6 +4,6 @@ require 'spec_helper'
 
 RSpec.describe GitlabSchema.types['Board'] do
   it 'includes the ee specific fields' do
-    expect(described_class).to have_graphql_field('weight')
+    expect(described_class).to have_graphql_fields(:weight, :epic_groups)
   end
 end