From: "osyoyu (Daisuke Aritomo) via ruby-core" <ruby-core@...>
Date: 2025-12-15T09:59:41+00:00
Subject: [ruby-core:124202] [Ruby Bug#21782] Ractor::IsolationError reports incorrect path for constants found through upwards search

Issue #21782 has been updated by osyoyu (Daisuke Aritomo).


Patch submitted: https://github.com/ruby/ruby/pull/15556

----------------------------------------
Bug #21782: Ractor::IsolationError reports incorrect path for constants found through upwards search
https://bugs.ruby-lang.org/issues/21782#change-115676

* Author: osyoyu (Daisuke Aritomo)
* Status: Open
* ruby -v: ruby 4.0.0dev (2025-12-15T07:05:21Z master 5a4faaaeb1) +PRISM [arm64-darwin24]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
Ractor::IsolationError is raised when non-main Ractors attempt access to non-shareable constants. The message contains the path to the constant which triggered the violation.
However, the path is incorrect when the constant was resolved through recursive search.

## Repro

Run the this Ruby program:

```ruby
TOPLEVEL = [1]

module M
  def self.f
    TOPLEVEL
  end
end

Ractor.new { M.f }.value
```

### Expected

Raises Ractor::IsolationError reporting that illegal access occured on `Object::TOPLEVEL` or `TOPLEVEL`

```
bug.rb:5:in 'M.f': can not access non-shareable objects in constant Object::TOPLEVEL by non-main Ractor. (Ractor::IsolationError)
        from bug.rb:9:in 'block in <main>'
```

### Actual

Raises Ractor::IsolationError reporting that illegal access occured on `M::TOPLEVEL`, which is incorrect. `TOPLEVEL` cannot be accessed as `M::TOPLEVEL`.


```
bug.rb:5:in 'M.f': can not access non-shareable objects in constant M::TOPLEVEL by non-main Ractor. (Ractor::IsolationError)
        from bug.rb:9:in 'block in <main>'
```

## Suspected code

This message is constructed in `rb_const_get_0()` defined in variable.c.

```c
static VALUE
rb_const_get_0(VALUE klass, ID id, int exclude, int recurse, int visibility)
{
    VALUE c = rb_const_search(klass, id, exclude, recurse, visibility);
    if (!UNDEF_P(c)) {
        if (UNLIKELY(!rb_ractor_main_p())) {
            if (!rb_ractor_shareable_p(c)) {
                rb_raise(rb_eRactorIsolationError, "can not access non-shareable objects in constant %"PRIsVALUE"::%s by non-main Ractor.", rb_class_path(klass), rb_id2name(id));
            }
        }
        return c;
    }
    return rb_const_missing(klass, ID2SYM(id));
}
```

The path part is built as `rb_class_path(klass)`, but `klass` may not be the module/class which the constant belongs, when the constant was found through recursive search in `rb_const_search`.



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