Classes or modules in explicit namespaces are not found

[fxn]

The root problem

This is really a bug in the current Ruby 2.5, but I open an issue here for reference.

Ruby 2.6 does not have this problem. The fix was backported to 2.5, so in principle should be fine in some future release.

How it affects Rails 6 Beta 2

When bootsnap loads bytecodes from its cache, Ruby 2.5 does not trigger :class events, but Zeitwerk needs them to be aware of children in explicit namespaces.

That means the if you have a namespace defined in a file like Hotel here:

# app/models/hotel.rb
class Hotel < ApplicationRecord
  include Pricing
end

# app/models/hotel/pricing.rb
module Hotel::Pricing
end

Zeitwerk won't be aware of the existence of Hotel::Pricing and loading Hotel will err.

You can see this problem in a brand new 6.0.0.beta2 app running Ruby 2.5.3:

$ bin/rails runner 'p ActionMailbox::InboundEmail::Incineratable'
Running via Spring preloader in process 18858
Please specify a valid ruby command or the path of a script to run.
Run 'rails runner -h' for help.

uninitialized constant #<Class:0x00007f8c177664e8>::Incineratable
Did you mean?  ActionMailbox::IncinerationJob

Workarounds

If your application is affected by this you have three options:

• Upgrade to Ruby 2.6.

• Disable the bytecode cache of bootsnap in config/boot.rb this way:

  # In config/boot.rb, replace require "bootsnap/setup" with the following.
  require "bootsnap"
  Bootsnap.setup(
    cache_dir: "tmp/cache",
    development_mode: ENV["RAILS_ENV"] == "development",
    compile_cache_iseq: false
  )

• Enable classic mode in config/application.rb:

  config.load_defaults 6.0
  config.autoloader = :classic

[fxn]

I just checked 2.5.4p155, and the issue seems to be still present.

[dhh]

@fxn How about we just set config.autoloader = :zeitwerk (or whatever it is) for newly generated applications? Then people with existing applications can switch at their leisure and compatibility?

[dhh]

Sounds like @rafaelfranca would like to just fix this in bootsnap by disabling the iseq cache for 2.5 👍

[rafaelfranca]

PR is up Shopify/bootsnap#257

[rafaelfranca]

Bootsnap 1.4.4 released with the fix.

[obromios]

I had this problem with rails 6.0.2 and ruby 2.5 so upgraded to ruby 2.6.5 and bootsnap 1.4.5 and it has mostly fixed the problem. However am seeing a strange effect when I run rails console. The first time I run it I get an exception:

app/helpers/eclubs/members_helper.rb:1:in `<main>': uninitialized constant Eclubs
Did you mean?  Club (NameError)

The relevant file is

#app/helpers/eclubs/members_helper.rb
module Eclubs::MembersHelper
end

But if I immediately exit and run console again it loads up correctly. Do you think this is related and how do I fix it?

[fxn]

That is very strange:

% cat app/helpers/eclubs/members_helper.rb
module Eclubs::MembersHelper
end
% bin/rails c
Loading development environment (Rails 6.0.2.1)
irb(main):001:0> Eclubs::MembersHelper
=> Eclubs::MembersHelper

Could you please throw

Rails.autoloaders.log!

in config/application.rb after the line that loads the framework defaults, trigger the error, and share the output?

[obromios]

@fxn, I have added the autoloaders command but am having trouble duplicating exception. I will explore further and come back to you.

[obromios]

@fxn, I solved the problem, thanks to your suggestion to use Rails.autoloaders.log!. The log showed that immediately prior to the exception occuring there was the following line;

Zeitwerk@rails.main: constant EclubsHelper loaded from file app/helpers/eclubs_helper.rb

Prior to creating the Eclubs namespace, the rails generator had created an unused file
#app/helpers/eclubs_helper.rb

module EclubsHelper
end

The solution in this case was just to delete app/helpers/eclubs_helper.rb.

I have a work flow of creating name spaces after a particular controller became too complex, which means there were quite a few other cases of having an ordinary (non namespaced) helper clashing with the namespace. For some reason everything would normally load OK, but then occasionally an exception would be thrown on one of the these duplicate name clashes. I will refactor these duplicates, unless you can suggest an easier fix.

Thank you for your help.

[obromios]

Having eliminated all helpers with a name starting with admin_, I am still intermittently seeing this problem. Below is a file with the output with Rails.autoloaders.log! enabled.

The exception occurs at line 556. The file that is causing the exception contains the following:

module Admin::ProfessionalContactsHelper
end

This occurs intermittently when I start rails console. It can also happen in a rspec test, but if I stop spring and rerun the test it is fixed.

I am not sure if it is related, but I am also having another issue with the loading process.

temp_zeitwert.txt

[fxn]

Hi @obromios, I have created #38365 to work on it, since this issue was about something that happened during betas with some sspecific versions of stuff. What you describe in principle should not be related to this.