Bug #21671: Rails CI raises `Assertion Failed: rbimpl_rstring_getmem:RB_TYPE_P(str, RUBY_T_STRING): actual type: 26` with "-DENABLE_PATH_CHECK=0 -DRUBY_DEBUG=1" enabled

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: ruby 3.5.0dev (2025-10-28T15:44:25Z master 7a736545e9) +PRISM [x86_64-linux]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN

[yahonda (Yasuo Honda)]

Recently Rails CI using "-DENABLE_PATH_CHECK=0 -DRUBY_DEBUG=1" enabled ruby raises Assertion Failed: rbimpl_rstring_getmem:RB_TYPE_P(str, RUBY_T_STRING): actual type: 26 assertion failures.

https://buildkite.com/rails/rails-nightly/builds/3121#019a5af8-b2a1-4289-a791-3fefc14a2a41/1447-1452

Steps to reproduce

1. Build Ruby with this configure option

./configure --prefix="/home/yahonda/.local/share/mise/installs/ruby/trunk" cppflags="-DENABLE_PATH_CHECK=0 -DRUBY_DEBUG=1" optflags="-O3 -fno-inline" --disable-install-doc

2. Clone Rails repository and run Active Job integration tests

git clone https://github.com/rails/rails
cd rails/activejob
bundle update --bundler
bundle install
bundle exec rake test:integration

Expected behavior

All of tests should pass.

Actual behavior

It usually raises ./include/ruby/internal/core/rstring.h:391: Assertion Failed: rbimpl_rstring_getmem:RB_TYPE_P(str, RUBY_T_STRING): actual type: 26
I have attached the entire output as assertion_failed.log

[yahonda (Yasuo Honda)]

I tried to identify which commit introduces this assertion failure but not found.

[byroot (Jean Boussier)]

The failure comes from rb_intern3 -> sym_find_or_insert_static_symbol (during Prism parsing).

cc @luke-gru (Luke Gruber) and @jhawthorn (John Hawthorn), maybe this ring a bell?