Can't modify frozen autoload_paths in development environment

[ortegacmanuel]

Steps to reproduce

1. Add gem "view_component" to Gemfile
2. Add require "view_component/engine" to config/application.rb
3. Run bin/rails generate component Example title content

Expected behavior

1. The generator creates all files/templates for the new new ViewComponent

Actual behavior

1. The generator crashes with the following errror:

`<<': can't modify frozen #<Class:#Array:0x00007ff3e041bcf8> (FrozenError

/home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/change_observer.rb:10:in `<<': can't modify frozen #<Class:#<Array:0x00007ff3e041bcf8>> (FrozenError)
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/change_observer.rb:10:in `<<'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/view_component-2.7.0/lib/view_component/engine.rb:29:in `block in <class:Engine>'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/railties-6.0.2.1/lib/rails/initializable.rb:32:in `instance_exec'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/railties-6.0.2.1/lib/rails/initializable.rb:32:in `run'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/railties-6.0.2.1/lib/rails/initializable.rb:61:in `block in run_initializers'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:228:in `block in tsort_each'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:350:in `block (2 levels) in each_strongly_connected_component'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:431:in `each_strongly_connected_component_from'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:349:in `block in each_strongly_connected_component'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in `each'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in `call'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:347:in `each_strongly_connected_component'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:226:in `tsort_each'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/2.5.0/tsort.rb:205:in `tsort_each'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/railties-6.0.2.1/lib/rails/initializable.rb:60:in `run_initializers'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/railties-6.0.2.1/lib/rails/application.rb:363:in `initialize!'
	from /home/manuel/kodo/main-street/mainstreet/config/environment.rb:5:in `<top (required)>'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `require'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:22:in `block in require_with_bootsnap_lfi'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/loaded_features_index.rb:92:in `register'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:21:in `require_with_bootsnap_lfi'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/bootsnap-1.4.5/lib/bootsnap/load_path_cache/core_ext/kernel_require.rb:30:in `require'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/zeitwerk-2.2.2/lib/zeitwerk/kernel.rb:23:in `require'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/activesupport-6.0.2.1/lib/active_support/dependencies.rb:325:in `block in require'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/activesupport-6.0.2.1/lib/active_support/dependencies.rb:291:in `load_dependency'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/activesupport-6.0.2.1/lib/active_support/dependencies.rb:325:in `require'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:106:in `preload'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:157:in `serve'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:145:in `block in run'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:139:in `loop'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application.rb:139:in `run'
	from /home/manuel/.rvm/gems/ruby-2.5.1/gems/spring-2.1.0/lib/spring/application/boot.rb:19:in `<top (required)>'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	from /home/manuel/.rvm/rubies/ruby-2.5.1/lib/ruby/site_ruby/2.5.0/rubygems/core_ext/kernel_require.rb:54:in `require'
	from -e:1:in `<main>'

System configuration

Rails version: Rails 6.0.2.1

Ruby version: ruby 2.5.1p57 (2018-03-29 revision 63029) [x86_64-linux]

Gem version: view_component-2.7.0

   # config/application.rb
   require 'rails/all'
   require "view_component/engine"
   module MyApp
    class Application < Rails::Application
      ...
      config.load_defaults "6.0"
      ...
    end
  end

[joelhawksley]

@ortegacmanuel thank you for the report and for the proposed fix! Would you be willing to provide a demo Rails application with this issue?

@vinistock @juanmanuelramallo as creators of the generator and previews (where this exception is being raised: lib/view_component/engine.rb:29), do you have any thoughts on the best resolution here?

As an aside, I'm wondering if this exception involving bootsnap is a sign that we should start testing for bootsnap compatibility in our test suite. Perhaps that's something you could look into @ortegacmanuel? Having our suite fail on an error like this would be ideal.

[juanmanuelramallo]

It might be related to:

https://guides.rubyonrails.org/autoloading_and_reloading_constants.html#autoload-paths

We are mutating it directly https://github.com/github/view_component/blob/master/lib/view_component/engine.rb#L29

[vinistock]

I think it's worth trying out what @juanmanuelramallo pointed out. We should always prefer the public API anyways and it might be the underlying issue.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[tvdeyen]

This is still an issue, because you are still mutating the ActiveSupport::Dependencies.autoload_paths array.

view_component/lib/view_component/engine.rb

Lines 83 to 84 in e85b23b

	paths_to_add = options.preview_paths - ActiveSupport::Dependencies.autoload_paths
	ActiveSupport::Dependencies.autoload_paths.concat(paths_to_add) if paths_to_add.any?

This happens only if paths_to_add.any?, which only happens if other paths than the default test/components/previews are used (ie. spec/components/previews) or if you add component previews from an Rails engine.

This is fixed by using test/components/previews in a Rails application, but still this is an unresolved issue for engine authors or people using non-default preview_paths.

[tvdeyen]

Fixed by #2182