[ruby-core:121957] [Ruby Bug#21321] Namespaces do not support extending mixins

10 May 2025

      Issue #21321 has been updated by fxn (Xavier Noria).

Maybe the root cause is _enabling_ namespaces with `RUBY_NAMESPACE=1`.

----------------------------------------
Bug #21321: Namespaces do not support extending mixins
https://bugs.ruby-lang.org/issues/21321#change-113071

* Author: fxn (Xavier Noria)
* Status: Open
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
The program

```ruby
module M
end

class C
  extend M
end
```

fails under a namespace with error:

```
'Kernel#extend': Cannot extend object with refinement (TypeError)
```

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