I ran into this issue:

/Users/amirsharif/.rvm/gems/ruby-2.7.5/gems/activesupport-7.0.2.3/lib/active_support/xml_mini.rb:184:in `current_thread_backend': uninitialized constant ActiveSupport::XmlMini::IsolatedExecutionState (NameError)

When running fontello open after upgrading to Rails 7.

Adding the following line:

require "active_support/isolated_execution_state"

to

/Users/amirsharif/.rvm/gems/ruby-2.7.5/bundler/gems/fontello_rails_converter-2bc7e117256e/lib/fontello_rails_converter.rb

resolved it.

I think we can create a PR for this, I will get around to it if someone can tell me the best way to add it.