Fix issue redirects going to /issues/:id/designs

When a project is redirected to a new project, Rails attempts to
construct the proper URL in `url_for` by finding the first route that
matches the given parameters. In this case, `namespace_id`,
`project_id`, `id` matched the `/designs` route first, so it used that.

This happens because the Rails `resources` block defines all the
standard #index, #show, #update, etc. routes after the block runs.

To ensure that `/issues/:id` is used to display an issue, we need to use
a separate action for `/issues/:id/designs`.

Closes https://gitlab.com/gitlab-org/gitlab/issues/31357

app/assets/javascripts/pages/projects/issues/designs/index.js

+import '../show/index';

app/controllers/concerns/issuable_actions.rb

@@ -30,6 +30,7 @@ module IssuableActions
     respond_to do |format|
       format.html do
         @issuable_sidebar = serializer.represent(issuable, serializer: 'sidebar') # rubocop:disable Gitlab/ModuleWithInstanceVariables
+        render 'show'
       end
 
       format.json do

app/controllers/projects/issues_controller.rb

@@ -21,7 +21,8 @@ class Projects::IssuesController < Projects::ApplicationController
   prepend_before_action(only: [:index]) { authenticate_sessionless_user!(:rss) }
   prepend_before_action(only: [:calendar]) { authenticate_sessionless_user!(:ics) }
   prepend_before_action :authenticate_user!, only: [:new]
-  prepend_before_action :store_uri, only: [:new, :show]
+  # designs is only applicable to EE, but defining a prepend_before_action in EE code would overwrite this
+  prepend_before_action :store_uri, only: [:new, :show, :designs]
 
   before_action :whitelist_query_limiting, only: [:create, :create_merge_request, :move, :bulk_update]
   before_action :check_issues_available!
@@ -43,6 +44,8 @@ class Projects::IssuesController < Projects::ApplicationController
 
   respond_to :html
 
+  alias_method :designs, :show
+
   def index
     @issues = @issuables
 

config/routes/project.rb

@@ -518,7 +518,7 @@ constraints(::Constraints::ProjectUrlConstrainer.new) do
           get :discussions, format: :json
 
           Gitlab.ee do
-            get 'designs(/*vueroute)', to: 'issues#show', as: :designs, format: false
+            get 'designs(/*vueroute)', to: 'issues#designs', as: :designs, format: false
           end
         end
 

ee/app/assets/javascripts/pages/projects/issues/designs/index.js

+import '../show/index';

ee/changelogs/unreleased/sh-fix-project-issue-redirects.yml

+---
+title: Fix issue redirects going to /issues/:id/designs
+merge_request: 16638
+author:
+type: fixed

ee/spec/controllers/projects/issues_controller_spec.rb

@@ -239,6 +239,33 @@ describe Projects::IssuesController do
     end
   end
 
+  describe 'GET #designs' do
+    context 'when project has moved' do
+      let(:new_project) { create(:project) }
+      let(:issue) { create(:issue, project: new_project) }
+
+      before do
+        sign_in(user)
+
+        project.route.destroy
+        new_project.redirect_routes.create!(path: project.full_path)
+        new_project.add_developer(user)
+      end
+
+      it 'redirects from an old issue/designs correctly' do
+        get :designs,
+            params: {
+              namespace_id: project.namespace,
+              project_id: project,
+              id: issue
+            }
+
+        expect(response).to redirect_to(designs_project_issue_path(new_project, issue))
+        expect(response).to have_gitlab_http_status(302)
+      end
+    end
+  end
+
   describe 'GET #discussions' do
     let(:issue) { create(:issue, project: project) }
     let!(:discussion) { create(:discussion_note_on_issue, noteable: issue, project: issue.project) }

spec/controllers/projects/issues_controller_spec.rb

@@ -36,6 +36,31 @@ describe Projects::IssuesController do
           expect(response).to render_template(:index)
         end
       end
+
+      context 'when project has moved' do
+        let(:new_project) { create(:project) }
+        let(:issue) { create(:issue, project: new_project) }
+
+        before do
+          project.route.destroy
+          new_project.redirect_routes.create!(path: project.full_path)
+          new_project.add_developer(user)
+        end
+
+        it 'redirects to the new issue tracker from the old one' do
+          get :index, params: { namespace_id: project.namespace, project_id: project }
+
+          expect(response).to redirect_to(project_issues_path(new_project))
+          expect(response).to have_gitlab_http_status(302)
+        end
+
+        it 'redirects from an old issue correctly' do
+          get :show, params: { namespace_id: project.namespace, project_id: project, id: issue }
+
+          expect(response).to redirect_to(project_issue_path(new_project, issue))
+          expect(response).to have_gitlab_http_status(302)
+        end
+      end
     end
 
     context 'internal issue tracker' do