Extract EE specific lines from issue.rb

Revert module include change

Aligned EE IssuesController with CE IssuesController

Aligned Issuable with CE version

Move Epic check to the right module

Extract milestone availability check from Issuable modules

Add specs for IssuableMilestoneAvailability

Remove service class and use override check on EE/Issuable instead

app/controllers/projects/issues_controller.rb

@@ -10,11 +10,11 @@ class Projects::IssuesController < Projects::ApplicationController
   include SpammableActions
   include RecordUserLastActivity
 
-  def issue_except_actions
+  def self.issue_except_actions
     %i[index calendar new create bulk_update import_csv]
   end
 
-  def set_issuables_index_only_actions
+  def self.set_issuables_index_only_actions
     %i[index calendar]
   end
 
@@ -25,9 +25,9 @@ class Projects::IssuesController < Projects::ApplicationController
 
   before_action :whitelist_query_limiting, only: [:create, :create_merge_request, :move, :bulk_update]
   before_action :check_issues_available!
-  before_action :issue, unless: ->(c) { c.issue_except_actions.include?(c.action_name.to_sym) }
+  before_action :issue, except: issue_except_actions
 
-  before_action :set_issuables_index, if: ->(c) { c.set_issuables_index_only_actions.include?(c.action_name.to_sym) }
+  before_action :set_issuables_index, only: set_issuables_index_only_actions
 
   # Allow write(create) issue
   before_action :authorize_create_issue!, only: [:new, :create]

app/models/concerns/issuable.rb

@@ -128,12 +128,6 @@ module Issuable
       assignees.count > 1
     end
 
-    def milestone_available?
-      return true if is_a?(Epic)
-
-      project_id == milestone&.project_id || project.ancestors_upto.compact.include?(milestone&.group)
-    end
-
     private
 
     def milestone_is_valid
@@ -279,6 +273,10 @@ module Issuable
     end
   end
 
+  def milestone_available?
+    project_id == milestone&.project_id || project.ancestors_upto.compact.include?(milestone&.group)
+  end
+
   def assignee_or_author?(user)
     author_id == user.id || assignees.exists?(user.id)
   end

ee/app/models/concerns/ee/issuable.rb

@@ -3,6 +3,7 @@
 module EE
   module Issuable
     extend ActiveSupport::Concern
+    extend ::Gitlab::Utils::Override
 
     class_methods do
       def labels_hash
@@ -17,6 +18,13 @@ module EE
       end
     end
 
+    override :milestone_available?
+    def milestone_available?
+      return true if is_a?(Epic)
+
+      super
+    end
+
     def supports_epic?
       is_a?(Issue) && project.group
     end

ee/spec/models/concerns/ee/issuable_spec.rb

@@ -19,4 +19,22 @@ describe EE::Issuable do
       expect(relation.labels_hash[issue_id]).to include('Feature', 'Second Label')
     end
   end
+
+  describe '#milestone_available?' do
+    context 'with Epic' do
+      let(:epic) { create(:epic) }
+
+      it 'returns true' do
+        expect(epic.milestone_available?).to be_truthy
+      end
+    end
+
+    context 'no Epic' do
+      let(:issue) { create(:issue) }
+
+      it 'returns false' do
+        expect(issue.milestone_available?).to be_falsy
+      end
+    end
+  end
 end