Fix "sign out" button in error pages

- Added some vanilla JS since we don't have
  rails_ujs here. If rails_ujs was here we could
  simple use data-method.

app/views/errors/_footer.html.haml

@@ -4,7 +4,8 @@
       = link_to s_('Nav|Home'), root_path
     %li
       - if current_user
-        = link_to s_('Nav|Sign out and sign in with a different account'), destroy_user_session_path, method: :post
+        = link_to s_('Nav|Sign out and sign in with a different account'), '#', id: 'sign_out_link'
+        %form{ action: destroy_user_session_path, method: :post, id: 'sign_out_form' }
       - else
         = link_to s_('Nav|Sign In / Register'), new_session_path(:user, redirect_to_referer: 'yes')
     %li

app/views/layouts/errors.html.haml

@@ -20,4 +20,10 @@
               history.back();
             });
           }
+
+          // We do not have rails_ujs here, so we're manually making a link trigger a form submit.
+          document.getElementById('sign_out_link').addEventListener('click', function(e) {
+            e.preventDefault();
+            document.getElementById('sign_out_form').submit();
+          });
         }());

changelogs/unreleased/322980-fix-sign-out-on-error-pages.yml

+---
+title: Fix sign out button in error pages
+merge_request: 59030
+author:
+type: fixed

spec/features/error_pages_spec.rb

@@ -2,7 +2,7 @@
 
 require 'spec_helper'
 
-RSpec.describe 'Error Pages' do
+RSpec.describe 'Error Pages', :js do
   let(:user) { create(:user) }
   let(:project) { create(:project, :public) }
 
@@ -14,7 +14,12 @@ RSpec.describe 'Error Pages' do
     it 'shows nav links' do
       expect(page).to have_link("Home", href: root_path)
       expect(page).to have_link("Help", href: help_path)
-      expect(page).to have_link(nil, href: destroy_user_session_path)
+    end
+
+    it 'allows user to sign out' do
+      click_link 'Sign out and sign in with a different account'
+
+      expect(page).to have_current_path(new_user_session_path)
     end
   end