[ruby-core:126615] [Ruby Bug#22273] Aliasing doesn't interact well with Module#prepend

9 Sep 2026

      Issue #22273 has been updated by Eregon (Benoit Daloze).

What if one actually wants to alias a method from a prepended module, how should they do it?

Maybe
```ruby
define_method(:my_alias, instance_method(:original))
```
?
That gives the same result.

---

My general thinking is `alias` and `alias_method` should do exactly the same as `define_method(alias_name, instance_method(original_name))`.
That would be so much easier to understand and much simpler semantically (ZSUPER aliases add so many complications).
Though in this issue it seems they are equivalent for this reproduction.

---

Mixing `prepend` (especially on `Kernel`) and `alias` works poorly in general, I think one should use one or the other.
Prepending on `Kernel` is very disruptive as it changes the ancestors of all classes (except direct subclasses of `BasicObject`).

----------------------------------------
Bug #22273: Aliasing doesn't interact well with Module#prepend
https://bugs.ruby-lang.org/issues/22273#change-118854

* Author: luke-gru (Luke Gruber)
* Status: Open
* Backport: 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN
----------------------------------------
Currently, aliasing doesn't interact well with `Module#prepend` in my opinion.

### Example

```ruby
module Kernel
  prepend(Module.new do
    def require(feature)
      puts "requiring feature (prepend): #{feature}"
      super
    end
  end)
end

module Kernel
  alias original_require require
  def require(feature)
    puts "requiring feature (alias): #{feature}"
    original_require(feature)
  end
end

require "set"
```

This produces this behavior:

```
requiring feature (prepend): set
requiring feature (alias): set
requiring feature (prepend): set
../ruby/test.rb:5:in 'require': super: no superclass method 'require' for main (NoMethodError)
```

I would expect this behavior:

```
requiring feature (prepend): set
requiring feature (alias): set
# Then, the original require would succeed
```

This has caused issues such as [22263](https://bugs.ruby-lang.org/issues/22263) and has [confused gem authors](https://github.com/fxn/zeitwerk/pull/203#issuecomment-1107777206). In the second link, the ignored alias was due to [this bug](https://github.com/ruby/ruby/commit/c59c4d717a2e687972341eab1574196e97d7d7be) which has recently been fixed.

### Bug?

As far as I know this is intentional behavior introduced in Ruby 2.0 [here](https://bugs.ruby-lang.org/issues/7842). There are even tests and specs that codify this behavior such as `test_prepend_super_in_alias` and `prepend_spec.rb`.

Even though it's intentional, I don't believe it's well thought out. I'm interested in hearing arguments for and against the current behavior (with code examples, preferably).

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