Issue #14006 has been reported by y-yagi (Yuji Yaginuma).

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Bug #14006: 2.5.0preview1でWarning.warnを再定義するとSystemStackErrorが発生する 
https://bugs.ruby-lang.org/issues/14006

* Author: y-yagi (Yuji Yaginuma)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN
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下記スクリプトを2.5.0.preview1で実行するとSystemStackErrorが発生します。 なお、下記スクリプトはRuby 2.4.1p111ではエラーが発生せず正常に動作します。

~~~ ruby
# warning_test.rb
module Warning
  def warn(message)
    return if message.match?("warning: possibly useless use of a variable in void context")

    super
  end
end

@a 
~~~ 

バックトレースは下記の通りです。

~~~ 
ruby -v warning_test.rb
ruby 2.5.0preview1 (2017-10-10 trunk 60153) [x86_64-linux]
warning_test.rb:9: warning: possibly useless use of a variable in void context
warning_test.rb:2: warning: method redefined; discarding old warn
Traceback (most recent call last):
	7580: from warning_test.rb:9:in `<main>'
	7579: from warning_test.rb:5:in `warn'
	7578: from warning_test.rb:5:in `warn'
	7577: from warning_test.rb:5:in `warn'
	7576: from warning_test.rb:5:in `warn'
	7575: from warning_test.rb:5:in `warn'
	7574: from warning_test.rb:5:in `warn'
	7573: from warning_test.rb:5:in `warn'
	 ... 7568 levels...
	   4: from warning_test.rb:5:in `warn'
	   3: from warning_test.rb:5:in `warn'
	   2: from warning_test.rb:5:in `warn'
	   1: from warning_test.rb:5:in `warn'
warning_test.rb:5:in `warn': stack level too deep (SystemStackError)
~~~ 

なお、再定義の方法を、

~~~ ruby 
def Warning.warn(message) 
  ... 
end 
~~~ 

のように変更すると、エラーが発生せず正常に動作します。
 
これは意図的な挙動でしょうか?




-- 
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