GitLab: how to defeat Rails "uninitialized constant" error?

Question

Ruby on Rails

Good time dear colleagues! Starting GitLab from source on an Apache and SSL machine using relative paths. Everything is more or less configured, the system components start up and work, but when web pages are requested, an error occurs in production.log:

Started GET "/gitlab/api/v4/internal/check" for 127.0.0.1 at 2018-06-16 09:31:18 +0000
Started GET "/gitlab/users/sign_in" for <IP> at 2018-06-16 09:31:53 +0000
Processing by SessionsController#new as HTML
Completed 500 Internal Server Error in 14ms (ActiveRecord: 1.6ms)

ActionView::Template::Error (uninitialized constant ActionView::CompiledTemplates::EXPR_ARG):
    1: %ul.nav-links.new-session-tabs.nav-tabs.nav{ role: 'tablist' }
    2:   %li.nav-item{ role: 'presentation' }
    3:     %a.nav-link.active{ href: '#login-pane', data: { toggle: 'tab' }, role: 'tab' } Sign in
    4:   - if allow_signup?
  app/views/devise/shared/_tabs_normal.html.haml:1:in `_app_views_devise_shared__tabs_normal_html_haml___3183421741055724100_47281175216580'
  app/views/devise/sessions/new.html.haml:7:in `_app_views_devise_sessions_new_html_haml__998010156118485515_47281178420240'
  app/controllers/sessions_controller.rb:22:in `new'
  lib/gitlab/i18n.rb:50:in `with_locale'
  lib/gitlab/i18n.rb:56:in `with_user_locale'
  app/controllers/application_controller.rb:362:in `set_locale'
  lib/gitlab/middleware/multipart.rb:95:in `call'
  lib/gitlab/request_profiler/middleware.rb:14:in `call'
  lib/gitlab/middleware/go.rb:17:in `call'
  lib/gitlab/etag_caching/middleware.rb:11:in `call'
  lib/gitlab/middleware/read_only/controller.rb:28:in `call'
  lib/gitlab/middleware/read_only.rb:16:in `call'
  lib/gitlab/request_context.rb:18:in `call'
  lib/gitlab/metrics/requests_rack_middleware.rb:27:in `call'
  lib/gitlab/middleware/release_env.rb:10:in `call'

I don't know Ruby, so I can't check the code. StackOverflow says that the Rails library is throwing the error.
Who faced? How can you win?

Answer 1

GitLab does not yet support Ruby 2.5.
Use 2.4.