Bug #21830: Ruby::Box and Kernel#require

• Status: Open
• Assignee: tagomoris (Satoshi Tagomori)
• Target version: -
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[fxn (Xavier Noria)]

If you enable Ruby::Box, decorations to Kernel#require do not work.

For example, given foo.rb:

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 it does not 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).

Bootsnap also depends on the ability of decorating Kernel#require (done here).

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

/cc @byroot (Jean Boussier) (Jean Boussier)

[fxn (Xavier Noria)]

• Description updated (diff)

[fxn (Xavier Noria)]

Just in case it matters, let me also add that it is assumed that Module#autoload invokes Kernel#require as introduced in cd465d5.

Zeitwerk relies on this too, because the main intercepted require calls are coming from autoloads set by autoloaders.

[tagomoris (Satoshi Tagomori)]

• Assignee set to tagomoris (Satoshi Tagomori)

[tagomoris (Satoshi Tagomori)]

I'll work on #21881 to solve this problem.