Disable internal issue tracker if external tracker in use

Closes #2006

CHANGELOG

@@ -1,6 +1,7 @@
 Please view this file on the master branch, on stable branches it's out of date.
 
 v 7.14.0 (unreleased)
+  - Disable internal issue tracker controller if external tracker is used (Stan Hu)
   - Expire Rails cache entries after two weeks to prevent endless Redis growth
   - Add support for destroying project milestones (Stan Hu)
 

app/controllers/projects/issues_controller.rb

@@ -131,7 +131,7 @@ class Projects::IssuesController < Projects::ApplicationController
   end
 
   def module_enabled
-    return render_404 unless @project.issues_enabled
+    return render_404 unless @project.issues_enabled && @project.default_issues_tracker?
   end
 
   # Since iids are implemented only in 6.1

spec/controllers/projects/issues_controller_spec.rb

@@ -0,0 +1,37 @@
+require('spec_helper')
+
+describe Projects::IssuesController do
+  let(:project) { create(:project) }
+  let(:user)    { create(:user) }
+  let(:issue) { create(:issue, project: project) }
+
+  before do
+    sign_in(user)
+    project.team << [user, :developer]
+    controller.instance_variable_set(:@project, project)
+  end
+
+  describe "GET #index" do
+    it "returns index" do
+      get :index, namespace_id: project.namespace.id, project_id: project.id
+
+      expect(response.status).to eq(200)
+    end
+
+    it "returns 404 when issues are disabled" do
+      project.issues_enabled = false
+      project.save
+
+      get :index, namespace_id: project.namespace.id, project_id: project.id
+      expect(response.status).to eq(404)
+    end
+
+    it "returns 404 when external issue tracker is enabled" do
+      allow(project).to receive(:default_issues_tracker?).and_return(false)
+
+      get :index, namespace_id: project.namespace.id, project_id: project.id
+      expect(response.status).to eq(404)
+    end
+
+  end
+end