Support filtering by epics in IssuesFinder

- issues in subepics not incldued in the filter

ee/app/finders/ee/issues_finder.rb

@@ -11,13 +11,14 @@ module EE
 
       override :scalar_params
       def scalar_params
-        @scalar_params ||= super + [:weight]
+        @scalar_params ||= super + [:weight, :epic_id]
       end
     end
 
     override :filter_items
     def filter_items(items)
-      by_weight(super)
+      issues = by_weight(super)
+      by_epic(issues)
     end
 
     private
@@ -74,5 +75,23 @@ module EE
       end
     end
     # rubocop: enable CodeReuse/ActiveRecord
+
+    def by_epic?
+      params[:epic_id].present?
+    end
+
+    def filter_by_no_epic?
+      params[:epic_id].to_s.downcase == ::IssuesFinder::FILTER_NONE
+    end
+
+    def by_epic(items)
+      return items unless by_epic?
+
+      if filter_by_no_epic?
+        items.no_epic
+      else
+        items.in_epics(params[:epic_id])
+      end
+    end
   end
 end

ee/app/models/ee/issue.rb

@@ -19,7 +19,7 @@ module EE
       scope :order_weight_asc, -> { reorder ::Gitlab::Database.nulls_last_order('weight') }
       scope :order_created_at_desc, -> { reorder(created_at: :desc) }
       scope :service_desk, -> { where(author: ::User.support_bot) }
-
+      scope :no_epic, -> { left_outer_joins(:epic_issue).where(epic_issues: { epic_id: nil }) }
       scope :in_epics, ->(epics) do
         issue_ids = EpicIssue.where(epic_id: epics).select(:issue_id)
         id_in(issue_ids)

ee/spec/finders/issues_finder_spec.rb

@@ -11,8 +11,8 @@ describe IssuesFinder do
       let(:scope) { 'all' }
 
       describe 'filter by weight' do
-        set(:issue_with_weight_1) { create(:issue, project: project3, weight: 1) }
-        set(:issue_with_weight_42) { create(:issue, project: project3, weight: 42) }
+        let_it_be(:issue_with_weight_1) { create(:issue, project: project3, weight: 1) }
+        let_it_be(:issue_with_weight_42) { create(:issue, project: project3, weight: 42) }
 
         context 'filter issues with no weight' do
           let(:params) { { weight: Issue::WEIGHT_NONE } }
@@ -40,7 +40,7 @@ describe IssuesFinder do
       end
 
       context 'filtering by assignee IDs' do
-        set(:user3) { create(:user) }
+        let_it_be(:user3) { create(:user) }
         let(:params) { { assignee_ids: [user2.id, user3.id] } }
 
         before do
@@ -53,16 +53,44 @@ describe IssuesFinder do
           expect(issues).to contain_exactly(issue3)
         end
       end
+
+      context 'filter by epic' do
+        let_it_be(:group) { create(:group) }
+
+        let_it_be(:epic_1) { create(:epic, group: group) }
+        let_it_be(:epic_2) { create(:epic, group: group) }
+        let_it_be(:sub_epic) { create(:epic, group: group, parent: epic_1) }
+
+        let_it_be(:issue_1) { create(:issue, project: project1, epic: epic_1) }
+        let_it_be(:issue_2) { create(:issue, project: project1, epic: epic_2) }
+        let_it_be(:issue_subepic) { create(:issue, project: project1, epic: sub_epic) }
+
+        context 'filter issues with no epic' do
+          let(:params) { { epic_id: ::IssuesFinder::FILTER_NONE } }
+
+          it 'returns filtered issues' do
+            expect(issues).to contain_exactly(issue1, issue2, issue3, issue4)
+          end
+        end
+
+        context 'filter issues by epic' do
+          let(:params) { { epic_id: epic_1.id } }
+
+          it 'returns all issues in the epic, subepic issues excluded' do
+            expect(issues).to contain_exactly(issue_1)
+          end
+        end
+      end
     end
   end
 
   describe '#with_confidentiality_access_check' do
-    let(:guest) { create(:user) }
+    let_it_be(:guest) { create(:user) }
 
-    set(:authorized_user) { create(:user) }
-    set(:project) { create(:project, namespace: authorized_user.namespace) }
-    set(:public_issue) { create(:issue, project: project) }
-    set(:confidential_issue) { create(:issue, project: project, confidential: true) }
+    let_it_be(:authorized_user) { create(:user) }
+    let_it_be(:project) { create(:project, namespace: authorized_user.namespace) }
+    let_it_be(:public_issue) { create(:issue, project: project) }
+    let_it_be(:confidential_issue) { create(:issue, project: project, confidential: true) }
 
     context 'when no project filter is given' do
       let(:params) { {} }

ee/spec/models/issue_spec.rb

@@ -67,22 +67,32 @@ describe Issue do
       end
     end
 
-    describe '.in_epics' do
+    context 'epics' do
       let_it_be(:epic1) { create(:epic) }
       let_it_be(:epic2) { create(:epic) }
       let_it_be(:epic_issue1) { create(:epic_issue, epic: epic1) }
       let_it_be(:epic_issue2) { create(:epic_issue, epic: epic2) }
+      let_it_be(:issue_no_epic) { create(:issue) }
 
       before do
         stub_licensed_features(epics: true)
       end
 
+      describe '.no_epic' do
+        it 'returns only issues without an epic assigned' do
+          expect(described_class.count).to eq 3
+          expect(described_class.no_epic).to eq [issue_no_epic]
+        end
+      end
+
+      describe '.in_epics' do
         it 'returns only issues in selected epics' do
-        expect(described_class.count).to eq 2
+          expect(described_class.count).to eq 3
           expect(described_class.in_epics([epic1])).to eq [epic_issue1.issue]
         end
       end
     end
+  end
 
   describe 'validations' do
     subject { build(:issue) }