From: "Eregon (Benoit Daloze) via ruby-core" <ruby-core@...>
Date: 2023-01-06T15:37:48+00:00
Subject: [ruby-core:111702] [Ruby master Bug#18797] Third argument to Regexp.new is a bit broken

Issue #18797 has been updated by Eregon (Benoit Daloze).



Assignee set to jeremyevans0 (Jeremy Evans)

Target version set to 3.3



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Bug #18797: Third argument to Regexp.new is a bit broken

https://bugs.ruby-lang.org/issues/18797#change-101098



* Author: janosch-x (Janosch M��ller)

* Status: Open

* Priority: Normal

* Assignee: jeremyevans0 (Jeremy Evans)

* Target version: 3.3

* Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

----------------------------------------

## Situation



'n' or 'N' can be passed as a third argument to `Regexp.new`. However, the behavior is not the same as the literal `n`-flag or the `Regexp::NOENCODING` option, and it makes the `#encoding` of `Regexp` and `Regexp#source` diverge:



```ruby

/����/n # => SyntaxError

Regexp.new('����', Regexp::NOENCODING) # => RegexpError

re = Regexp.new('����', nil, 'n') # => /����/

re.options == Regexp::NOENCODING # => true

re.encoding # => ASCII-8BIT

re.source.encoding # => UTF-8

re =~ '����' # => Encoding::CompatibilityError

```



## Code



[Here](https://github.com/ruby/ruby/blob/b41de3a1e8c36a5cc336b6f7cd3cb71126cf1a60/re.c#L3622-L3658). There is also a test for the resulting encoding [here](https://github.com/ruby/ruby/blob/cf2bbcfff2985c116552967c7c4522f4630f2d18/test/ruby/test_regexp.rb#L564), but it is a no-op because the whole file is set to that encoding via magic comment anyway.



The third argument was added when ASCII was still the default Ruby encoding, so I guess Regexp and source encoding still matched at that point.



## Solution



It could be fixed, but my impression is that it is not useful anymore.



It was probably only added because `Regexp::NOENCODING` wasn't available at the time, so I think it could be deprecated like so:



> Passing a third argument to Regexp.new is deprecated. Use `Regexp::NOENCODING` as second argument instead.







-- 

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

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