Enable Epic relationships

- remove epic_links feature flag
- add documentation & changelog

doc/user/group/epics/index.md

@@ -23,6 +23,10 @@ you can change its title, description, start date, and due date.
 
 ![epic view](img/epic_view.png)
 
+## Relationship in Epics
+
+### With Issues
+
 An epic contains a list of issues, and an issue can be associated with at most
 one epic. You can add issues associated with the epic by clicking the
 plus icon (<kbd>+</kbd>) under the epic description, pasting the link of the
@@ -31,9 +35,19 @@ group or any of the epic's subgroups are eligible to be added. To remove an
 issue from an epic, simply click on the <kbd>x</kbd> button in the epic's
 issue list.
 
-When you add an issue to an epic that's already associated with another epic,
-the issue is automatically removed from the previous epic. In other words, an
-issue can be associated with at most one epic.
+### With Epics
+
+An epic can have multiple child epics while the maximum depth is 5. You can add epics associated with the epic by clicking the
+plus icon (<kbd>+</kbd>) under the epic description, pasting the link of the
+issue, and clicking **Add**. Any epic belonging to a group or subgroup of the epic's
+group are eligible to be added. To remove a child epic from a parent epic,
+simply click on the <kbd>x</kbd> button in the epic's epic list.
+
+### Conflicts
+
+When you add an issue or an epic to an epic that's already associated with another epic,
+the issue or the epic is automatically removed from the previous epic. In other words, an
+issue or epic can be associated with at most one epic.
 
 ## Start date and due date
 

ee/app/assets/javascripts/epics/epic_show/components/epic_show_app.vue

@@ -213,7 +213,7 @@ export default {
     return {
       // Epics specific configuration
       issuableRef: '',
-      hasRelatedEpicsFeature: this.subepicsSupported && gon.features && gon.features.epicLinks,
+      hasRelatedEpicsFeature: this.subepicsSupported,
       projectPath: this.groupPath,
       parentEpic: this.parent ? this.parent : {},
       projectNamespace: '',

ee/app/controllers/groups/epic_links_controller.rb

@@ -3,13 +3,8 @@
 class Groups::EpicLinksController < Groups::EpicsController
   include EpicRelations
 
-  before_action :check_feature_flag!
   before_action :check_nested_support!
 
-  before_action do
-    push_frontend_feature_flag(:epic_links)
-  end
-
   def destroy
     result = ::Epics::UpdateService.new(group, current_user, { parent: nil }).execute(child_epic)
 
@@ -30,10 +25,6 @@ class Groups::EpicLinksController < Groups::EpicsController
     @child_epic ||= Epic.find(params[:id])
   end
 
-  def check_feature_flag!
-    render_404 unless Feature.enabled?(:epic_links, group)
-  end
-
   def check_nested_support!
     render_404 unless Epic.supports_nested_objects?
   end

ee/app/controllers/groups/epics_controller.rb

@@ -8,10 +8,6 @@ class Groups::EpicsController < Groups::ApplicationController
   include RendersNotes
   include EpicsActions
 
-  before_action do
-    push_frontend_feature_flag(:epic_links)
-  end
-
   before_action :check_epics_available!
   before_action :epic, except: [:index, :create]
   before_action :set_issuables_index, only: :index

ee/changelogs/unreleased/8915-remove-epics-ff.yml

+---
+title: Add support for relationship between epics
+merge_request: 9051
+author:
+type: added

ee/spec/controllers/groups/epic_links_controller_spec.rb

@@ -26,20 +26,6 @@ describe Groups::EpicLinksController, :postgresql do
     end
   end
 
-  shared_examples 'feature flag disabled' do
-    before do
-      stub_licensed_features(epics: true)
-      stub_feature_flags(epic_links: false)
-      group.add_developer(user)
-
-      subject
-    end
-
-    it 'returns 400 status' do
-      expect(response).to have_gitlab_http_status(404)
-    end
-  end
-
   describe 'GET #index' do
     before do
       epic1.update(parent: parent_epic)
@@ -48,12 +34,10 @@ describe Groups::EpicLinksController, :postgresql do
     subject { get :index, group_id: group, epic_id: parent_epic.to_param }
 
     it_behaves_like 'unlicensed epics action'
-    it_behaves_like 'feature flag disabled'
 
-    context 'when epic_links feature is enabled' do
+    context 'when epics are enabled' do
       before do
         stub_licensed_features(epics: true)
-        stub_feature_flags(epic_linkcs: true)
         group.add_developer(user)
 
         subject
@@ -76,12 +60,10 @@ describe Groups::EpicLinksController, :postgresql do
     end
 
     it_behaves_like 'unlicensed epics action'
-    it_behaves_like 'feature flag disabled'
 
-    context 'when epic_links feature is enabled' do
+    context 'when epics are enabled' do
       before do
         stub_licensed_features(epics: true)
-        stub_feature_flags(epic_linkcs: true)
       end
 
       context 'when user has permissions to create requested association' do
@@ -124,12 +106,10 @@ describe Groups::EpicLinksController, :postgresql do
     subject { delete :destroy, group_id: group, epic_id: parent_epic.to_param, id: epic1.id }
 
     it_behaves_like 'unlicensed epics action'
-    it_behaves_like 'feature flag disabled'
 
-    context 'when epic_links feature is enabled' do
+    context 'when epics are enabled' do
       before do
         stub_licensed_features(epics: true)
-        stub_feature_flags(epic_linkcs: true)
       end
 
       context 'when user has permissions to update the parent epic' do