Fix commit signature error when project is disabled

When a project is disabled, visiting the home page would show,
"An error occurred while loading commit signatures". This change checks
that the user has permission to view the project to avoid unnecessary
GPG signature lookups.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/50903

app/views/projects/show.html.haml

@@ -8,8 +8,8 @@
 
 = render partial: 'flash_messages', locals: { project: @project }
 
-- if @project.repository_exists? && !@project.empty_repo?
-  - signatures_path = namespace_project_signatures_path(namespace_id: @project.namespace.full_path, project_id: @project.path, id: @project.default_branch)
+- if !@project.empty_repo? && can?(current_user, :download_code, @project)
+  - signatures_path = project_signatures_path(@project, @project.default_branch)
   .js-signature-container{ data: { 'signatures-path': signatures_path } }
 
 %div{ class: [container_class, ("limit-container-width" unless fluid_layout)] }

changelogs/unreleased/sh-fix-commit-signatures-error.yml

+---
+title: Fix commit signature error when project is disabled
+merge_request: 22344
+author:
+type: fixed

spec/features/projects_spec.rb

@@ -193,6 +193,23 @@ describe 'Project' do
     end
   end
 
+  describe 'when the project repository is disabled', :js do
+    let(:user)    { create(:user) }
+    let(:project) { create(:project, :repository_disabled, :repository, namespace: user.namespace) }
+
+    before do
+      sign_in(user)
+      project.add_maintainer(user)
+      visit project_path(project)
+    end
+
+    it 'does not show an error' do
+      wait_for_requests
+
+      expect(page).not_to have_selector('.flash-alert')
+    end
+  end
+
   describe 'removal', :js do
     let(:user)    { create(:user) }
     let(:project) { create(:project, namespace: user.namespace) }