From: "matz (Yukihiro Matsumoto)" <noreply@...>
Date: 2022-08-25T09:59:16+00:00
Subject: [ruby-core:109683] [Ruby master Bug#18797] Third argument to Regexp.new is a bit broken

Issue #18797 has been updated by matz (Yukihiro Matsumoto).


This is indeed an obsolete feature for long time. And the third argument is ignored (IIRC).
Some (old) gems still use it because they are not updated for long time. Warnings should not improve the situation (since most of them are unmaintained).
So we should update the document and leave the code as it is.

Matz.


----------------------------------------
Bug #18797: Third argument to Regexp.new is a bit broken
https://bugs.ruby-lang.org/issues/18797#change-98907

* Author: janosch-x (Janosch M��ller)
* Status: Open
* Priority: Normal
* 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.



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