Bug #21991: `$!` stays as the first exception in Ruby Box

• Status: Open
• Assignee: tagomoris (Satoshi Tagomori)
• Target version: -
• ruby -v: ruby 4.0.2 (2026-03-17 revision d3da9fec82) +PRISM [x86_64-darwin24]
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[tikkss (Tsutomu Katsube)]

Description

When Ruby Box is enabled (RUBY_BOX=1), $! inside rescue does not change after the first exception.

$! is expected to show the exception for each rescue block, but it always shows the first one.

Steps to reproduce

# test.rb
begin
  raise "First error"
rescue
  pp $!
end

begin
  raise "Second error"
rescue
  pp $!
end

begin
  raise "Third error"
rescue
  pp $!
end

Expected result

$ RUBY_BOX=1 ruby test.rb
ruby: warning: Ruby::Box is experimental, and the behavior may change in the future!
See https://docs.ruby-lang.org/en/4.0/Ruby/Box.html for known issues, etc.
#<RuntimeError: First error>
#<RuntimeError: Second error>
#<RuntimeError: Third error>

Actual result

$ RUBY_BOX=1 ruby test.rb
ruby: warning: Ruby::Box is experimental, and the behavior may change in the future!
See https://docs.ruby-lang.org/en/4.0/Ruby/Box.html for known issues, etc.
#<RuntimeError: First error>
#<RuntimeError: First error>
#<RuntimeError: First error>

Additional information

This issue does not reproduce when RUBY_BOX=1 is not set:

$ ruby test.rb
#<RuntimeError: First error>
#<RuntimeError: Second error>
#<RuntimeError: Third error>

Also, this issue does not reproduce when the exception object is captured explicitly in the rescue clause:

# test.rb
begin
  raise "First error"
rescue => e
  pp e
end

begin
  raise "Second error"
rescue => e
  pp e
end

begin
  raise "Third error"
rescue => e
  pp e
end

$ RUBY_BOX=1 ruby test.rb
ruby: warning: Ruby::Box is experimental, and the behavior may change in the future!
See https://docs.ruby-lang.org/en/4.0/Ruby/Box.html for known issues, etc.
#<RuntimeError: First error>
#<RuntimeError: Second error>
#<RuntimeError: Third error>

[byroot (Jean Boussier)]

• Related to Bug #21823: $! is nil inside rescue block when $! is accessed before raise in Ruby::Box added

[byroot (Jean Boussier)]

• Assignee set to tagomoris (Satoshi Tagomori)