From: "hsbt (Hiroshi SHIBATA) via ruby-core" <ruby-core@...>
Date: 2026-09-18T00:22:29+00:00
Subject: [ruby-core:126765] [Ruby Bug#22332] Ruby::Box: prelude is evaluated only in the master box, so pp and binding.irb load into it

Issue #22332 has been reported by hsbt (Hiroshi SHIBATA).

----------------------------------------
Bug #22332: Ruby::Box: prelude is evaluated only in the master box, so pp and binding.irb load into it
https://bugs.ruby-lang.org/issues/22332

* Author: hsbt (Hiroshi SHIBATA)
* Status: Open
* Assignee: tagomoris (Satoshi Tagomori)
* ruby -v: ruby 4.1.0dev (2026-09-17T00:01:17Z master 3f6143715a) [arm64-darwin27]
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
Under `RUBY_BOX=1`, `Kernel#pp` prints but leaves nothing behind in the box that called it.

```
$ RUBY_BOX=1 ruby --disable-gems -W:no-experimental -e 'pp({a: 1}); p $LOADED_FEATURES.grep(/pp\.rb/).size, defined?(PP)'
{a: 1}
0
nil

$ ruby --disable-gems -e 'pp({a: 1}); p $LOADED_FEATURES.grep(/pp\.rb/).size, defined?(PP)'
{a: 1}
1
"constant"
```

Requiring it afterwards therefore loads the same file a second time, and it redefines its own methods:

```
$ RUBY_BOX=1 ruby --disable-gems -W:no-experimental -e 'pp({a: 1}); require "pp"'
{a: 1}
.../lib/ruby/4.1.0+4/pp.rb:412: warning: method redefined; discarding old pretty_print
.../lib/ruby/4.1.0+4/pp.rb:412: warning: previous definition of pretty_print was here
(and 20 more)
```

A box created before the call cannot see it either, while one created afterwards inherits it from the master box:

```
$ RUBY_BOX=1 ruby --disable-gems -W:no-experimental -e 'before = Ruby::Box.new; pp({a: 1}); after = Ruby::Box.new; p before.eval("defined?(PP)"), after.eval("defined?(PP)")'
{a: 1}
nil
"constant"
```

`Binding#irb` fails outright, because its `rescue LoadError, Gem::LoadError` clause is evaluated where RubyGems is not loaded:

```
$ RUBY_BOX=1 ruby -W:no-experimental -e 'binding.irb' < /dev/null
-e:1:in 'Binding#irb': uninitialized constant Binding::Gem (NameError)
```

Without a box the same command starts irb.

`prelude.rb` is evaluated once in `rb_call_builtin_inits()` (`Init_builtin_prelude()`, `inits.c:114`), before the root and main boxes exist, so the box recorded on `Kernel#pp` and `Binding#irb` is the master box, and the `require` they run loads there. `gem_prelude` already avoids this: `rb_load_gem_prelude()` (`builtin.c:114`) runs for root and main in `Init_builtin_features()` and again for every new box (`box.c:435`).

So the question is where prelude should be evaluated. Three shapes I can see:

- load prelude per box the way gem_prelude already is (https://github.com/ruby/ruby/pull/18713);
- keep the single evaluation and mark the prelude methods `Primitive.attr! :caller_user_box`, so only their `require` resolves in the caller's box;
- make `require` called from a master-box method resolve in the caller's box in general, which needs care not to become local rebinding (#21362).

Is there another shape you would prefer?

Reproduced on master 3f6143715a and on released 4.0.7.

Related to #22275



-- 
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