Bug #22263
Updated by yahonda (Yasuo Honda) about 2 months ago
### 1. First occurrence in Rails CI
https://buildkite.com/rails/rails-nightly/builds/4651#01a016ac-eaf9-4a71-9fb6-1924c8a7b9af
(job "activemodel (master-debug)", 2026-08-18, ruby 4.1.0dev (2026-08-18T13:12:35Z master 6b719acc57) +PRISM [x86_64-linux])
Two Active Model tests ran a short-lived Ractor in the test process. A few seconds later, `RailtieTest` forked child processes (Active Support's fork-based test isolation), and the children failed while booting a Rails application.
### 2. Steps to reproduce
A Rails checkout is required. Verified with Rails main 0f36bbf72c and the `rubylang/ruby:master` Docker image (ruby 4.1.0dev (2026-08-25T07:50:12Z master 753ace46fe)); it reproduces every run.
```
$ git clone https://github.com/rails/rails && cd rails && bundle install
$ cd activemodel
$ bundle exec ruby -w -Ilib:test bin/test test/cases/naming_test.rb test/cases/railtie_test.rb
```
### 3. Expected behavior
The forked child behaves like its parent: the Rails application boots and the child exits with status 0 (`child: #<Process::Status: pid NNN exit 0>`). The test pair reports 0 errors.
### 4. Actual behavior
The forked child raises an exception during `require` and exits with status 1; the parent process is unaffected:
```
$ bundle exec ruby -w -Ilib:test bin/test test/cases/naming_test.rb test/cases/railtie_test.rb
Source locally installed gems is ignoring #<Bundler::StubSpecification name=psych version=5.5.0 platform=ruby> because it is missing extensions
Source locally installed gems is ignoring #<Bundler::StubSpecification name=prism version=1.9.0 platform=ruby> because it is missing extensions
Source locally installed gems is ignoring #<Bundler::StubSpecification name=io-console version=0.8.2 platform=ruby> because it is missing extensions
Source locally installed gems is ignoring #<Bundler::StubSpecification name=io-console version=0.9.2 platform=ruby> because it is missing extensions
Source locally installed gems is ignoring #<Bundler::StubSpecification name=erb version=6.0.7 platform=ruby> because it is missing extensions
Source locally installed gems is ignoring #<Bundler::StubSpecification name=date version=3.5.1 platform=ruby> because it is missing extensions
Run options: --seed 20598
# Running:
............................................................E
Error:
RailtieTest#test_i18n_customize_full_message_defaults_to_false:
NoMethodError: super: no superclass method 'require' for main
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'require'
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'Kernel#require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'Rails::Application#config'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/railtie.rb:148:in 'Rails::Railtie.config'
test/cases/railtie_test.rb:16:in 'block in RailtieTest#setup'
test/cases/railtie_test.rb:15:in 'Class#initialize'
test/cases/railtie_test.rb:15:in 'Class#new'
test/cases/railtie_test.rb:15:in 'RailtieTest#setup'
bin/test test/cases/railtie_test.rb:36
E
Error:
RailtieTest#test_secure_password_min_cost_is_false_in_the_development_environment:
NoMethodError: super: no superclass method 'require' for main
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'require'
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'Kernel#require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'Rails::Application#config'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/railtie.rb:148:in 'Rails::Railtie.config'
test/cases/railtie_test.rb:16:in 'block in RailtieTest#setup'
test/cases/railtie_test.rb:15:in 'Class#initialize'
test/cases/railtie_test.rb:15:in 'Class#new'
test/cases/railtie_test.rb:15:in 'RailtieTest#setup'
bin/test test/cases/railtie_test.rb:22
E
Error:
RailtieTest#test_i18n_customize_full_message_can_be_disabled:
NoMethodError: super: no superclass method 'require' for main
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'require'
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'Kernel#require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'Rails::Application#config'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/railtie.rb:148:in 'Rails::Railtie.config'
test/cases/railtie_test.rb:16:in 'block in RailtieTest#setup'
test/cases/railtie_test.rb:15:in 'Class#initialize'
test/cases/railtie_test.rb:15:in 'Class#new'
test/cases/railtie_test.rb:15:in 'RailtieTest#setup'
bin/test test/cases/railtie_test.rb:42
E
Error:
RailtieTest#test_secure_password_min_cost_is_true_in_the_test_environment:
NoMethodError: super: no superclass method 'require' for main
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'require'
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'Kernel#require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'Rails::Application#config'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/railtie.rb:148:in 'Rails::Railtie.config'
test/cases/railtie_test.rb:16:in 'block in RailtieTest#setup'
test/cases/railtie_test.rb:15:in 'Class#initialize'
test/cases/railtie_test.rb:15:in 'Class#new'
test/cases/railtie_test.rb:15:in 'RailtieTest#setup'
bin/test test/cases/railtie_test.rb:29
E
Error:
RailtieTest#test_i18n_customize_full_message_can_be_enabled:
NoMethodError: super: no superclass method 'require' for main
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'require'
/home/yahonda/.local/share/mise/installs/ruby/trunk/lib/ruby/gems/4.1.0+4/gems/zeitwerk-2.8.3/lib/zeitwerk/core_ext/kernel.rb:34:in 'Kernel#require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'require'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/application.rb:484:in 'Rails::Application#config'
/home/yahonda/src/github.com/rails/rails/railties/lib/rails/railtie.rb:148:in 'Rails::Railtie.config'
test/cases/railtie_test.rb:16:in 'block in RailtieTest#setup'
test/cases/railtie_test.rb:15:in 'Class#initialize'
test/cases/railtie_test.rb:15:in 'Class#new'
test/cases/railtie_test.rb:15:in 'RailtieTest#setup'
bin/test test/cases/railtie_test.rb:49
Finished in 0.088916s, 731.0243 runs/s, 820.9965 assertions/s.
65 runs, 73 assertions, 0 failures, 5 errors, 0 skips
$
```
### 5. Bisect result
```
c59c4d717a2e687972341eab1574196e97d7d7be 98f0921f2b06bcc6435fe96a99da3a857ac10477 introduces this behavior.
```