From: "tikkss (Tsutomu Katsube) via ruby-core" <ruby-core@...>
Date: 2026-04-10T21:34:41+00:00
Subject: [ruby-core:125235] [Ruby Bug#21991] `$!` stays as the first exception in Ruby Box

Issue #21991 has been reported by tikkss (Tsutomu Katsube).

----------------------------------------
Bug #21991: `$!` stays as the first exception in Ruby Box
https://bugs.ruby-lang.org/issues/21991

* Author: tikkss (Tsutomu Katsube)
* Status: Open
* 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
----------------------------------------
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
---

```ruby
# 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
---

```console
$ 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
---

```console
$ 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:

```console
$ 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:

```ruby
# 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
```

```console
$ 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>
```




-- 
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