[ruby-core:124462] [Ruby Bug#21830] Ruby::Box and Kernel#require

9 Jan 2026

      Issue #21830 has been updated by fxn (Xavier Noria).

If you enable Ruby::Box, decorations to `Kernel#require` do not work. For example, given _foo.rb_:

```ruby
module M
  def require(_path)
    puts 'decorated'
    super
  end
end

Kernel.prepend(M)

p require 'tsort'
```

the decoration works normally:

```
% ruby -v foo.rb
ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [arm64-darwin25]
decorated
true
```

but the same code does not work with the feature enabled:

```
% RUBY_BOX=1 ruby -v foo.rb
ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [arm64-darwin25]
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.
true
```

With this, Zeitwerk cannot work because it totally depends on a decoration of `Kernel#require` (done [here](https://github.com/fxn/zeitwerk/blob/main/lib/zeitwerk/core_ext/kernel.rb)).

Bootsnap also depends on the ability of decorating `Kernel#require` (done [here](https://github.com/rails/bootsnap/blob/main/lib/bootsnap/load_path_cache/cor...)).

On one hand, these gems are walking a fine line in the border of the public interface of Ruby. On the other hand, it is a goal of boxes to be transparent to the code being loaded under them.

@tagomoris (Satoshi Tagomori) what should be the way to go in your opinion?

/cc @byroot (Jean Boussier)

----------------------------------------
Bug #21830: Ruby::Box and Kernel#require
https://bugs.ruby-lang.org/issues/21830#change-116012

* Author: fxn (Xavier Noria)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
If you enable `Ruby::Box`, decorations to `Kernel#require` do not work. For example, given `foo.rb`:

```ruby
# foo.rb

% cat foo.rb
module M
  def require(_path)
    puts "decorated"
    super
  end
end

Kernel.prepend(M)

require 'tsort'
```

the decoration works normally:

```
% ruby -v foo.rb
ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [arm64-darwin25]
decorated
```

and the same code does not work with the feature enabled:

```
% RUBY_BOX=1 ruby -v foo.rb
ruby 4.0.0 (2025-12-25 revision 553f1675f3) +YJIT +PRISM [arm64-darwin25]
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.
```

With this, Zeitwerk cannot work because it totally depends on `Kernel#require` decoration (done [here](https://github.com/fxn/zeitwerk/blob/main/lib/zeitwerk/core_ext/kernel.rb)).

Bootsnap also depends on the ability of decorating `Kernel#require` (done [here](https://github.com/rails/bootsnap/blob/main/lib/bootsnap/load_path_cache/cor...)).

On one hand, these gems are walking a fine line in the border of the public interface of Ruby. On the other hand, it is a goal of boxes to be transparent to the code being loaded under them.

@tagomoris what should be the way to go in your opinion?

/cc @byroot

-- 
https://bugs.ruby-lang.org/