Zeitwerk support

[sanak]

Problem When using Redmine master (trunk) branch, this plugin installation (bundle exec rake redmine:plugins:migrate) fails with the following error.

$ bundle exec rake redmine:plugins:migrate
rake aborted!
LoadError: cannot load such file -- redmine_custom_fields_groups
/Users/sanak/Build/rb/redmine/vendor/bundle/ruby/2.7.0/gems/polyglot-0.3.5/lib/polyglot.rb:65:in `require'
/Users/sanak/Build/rb/redmine/vendor/bundle/ruby/2.7.0/gems/polyglot-0.3.5/lib/polyglot.rb:65:in `require'
/Users/sanak/Build/rb/redmine/vendor/bundle/ruby/2.7.0/gems/zeitwerk-2.5.3/lib/zeitwerk/kernel.rb:35:in `require'
/Users/sanak/Build/rb/redmine/plugins/redmine_custom_fields_groups/init.rb:1:in `<top (required)>'
/Users/sanak/Build/rb/redmine/lib/redmine/plugin_loader.rb:31:in `load'
/Users/sanak/Build/rb/redmine/lib/redmine/plugin_loader.rb:31:in `run_initializer'
/Users/sanak/Build/rb/redmine/lib/redmine/plugin_loader.rb:111:in `each'
/Users/sanak/Build/rb/redmine/lib/redmine/plugin_loader.rb:111:in `block in load'
:

Supporting Zeitwerk is necessary, because upcoming Redmine version (5.0) uses it. Here is the some links:

• Feature #32938: Rails 6: Zeitwerk support - Redmine
• Defect #36245: ActiveSupport::Reloader.to_prepare not working in trunk 21287 - Redmine