From: merch-redmine@...
Date: 2020-03-24T21:16:30+00:00
Subject: [ruby-core:97589] [Ruby master Bug#16736] Prepending blank module breaks super call in aliased method

Issue #16736 has been updated by jeremyevans0 (Jeremy Evans).


Pull request submitted: https://github.com/ruby/ruby/pull/2978

This includes a GC change to prevent a use-after-free, but I'm not sure if the change introduces a memory leak.  Someone that knows more about GC and in what cases iclasses share method tables should probably review.

This pull request also fixes an issue in `Module#included_modules` to handle origin iclasses for modules correctly.

----------------------------------------
Bug #16736: Prepending blank module breaks super call in aliased method
https://bugs.ruby-lang.org/issues/16736#change-84772

* Author: tycooon (Yuri Smirnov)
* Status: Assigned
* Priority: Normal
* Assignee: jeremyevans0 (Jeremy Evans)
* ruby -v: 2.7.0p0 (2019-12-25 revision 647ee6f091) [x86_64-darwin19]
* Backport: 2.5: DONTNEED, 2.6: DONTNEED, 2.7: REQUIRED
----------------------------------------
Here is the test script:

```
class A
  def key
    ["some_key"]
  end
end

module M
  prepend Module.new

  def self.included(base)
    base.alias_method :base_key, :key
  end

  def key
    super + ["new_key"]
  end

  def generate
    base_key
  end
end

class B < A
  include M
end

x = B.new
p x.generate

```

In Ruby 2.7 I get the following error:

```
Traceback (most recent call last):
	2: from test.rb:28:in `<main>'
	1: from test.rb:19:in `generate'
test.rb:15:in `key': super: no superclass method `key' for #<B:0x00007fbc1704d028> (NoMethodError)
```

If I remove the `prepend Module.new` line or switch to Ruby 2.6, I get the expected result:

```
["some_key", "new_key"]
```



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