Merge branch 'disable-internal-tracker-when-external-in-use' into 'master'

Disable internal issue tracker if external tracker in use

### What does this MR do?

This MR disables routes to the internal issue tracker if an external issue tracker (e.g. Redmine) is in use. A 404 page is returned if a user attempts to access any of the issue routes.

### Why was this MR needed?

Enabling the external issue tracker would still keep the internal one active, which would lead to odd behavior where users could create issues but not close them.

### What are the relevant issue numbers?

Closes #2006

See merge request !993

CHANGELOG

@@ -28,6 +28,7 @@ v 7.14.0 (unreleased)
   - Fix file upload dialog for comment editing (Daniel Gerhardt)
   - Set OmniAuth full_host parameter to ensure redirect URIs are correct (Stan Hu)
   - Return comments in created order in merge request API (Stan Hu)
+  - 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)
   - Allow custom backup archive permissions

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