[ruby-core:103836] [Ruby master Bug#14367] Wrong interpretation of backslash C in regexp literals

Issue #14367 has been updated by jeremyevans0 (Jeremy Evans).


jeremyevans0 (Jeremy Evans) wrote in #note-8:
> nobu (Nobuyoshi Nakada) wrote in #note-7:
> > Agree that the previous behavior might not be intentional, but commit:11ae581a4a7f5d5f5ec6378872eab8f25381b1b9 also seems something broken on other than US-ASCII encoding.
> > 
> > ```
> > $ LANG=en_US.UTF-8 ./ruby -vce '/\c\xFF/'
> > ruby 3.1.0dev (2021-05-13T01:55:43Z master 11ae581a4a) [x86_64-darwin19]
> > -e:1: invalid multibyte escape: /\x9F/
> > -e:1: warning: possibly useless use of a literal in void context
> > ```
> 
> The previous behavior also ended up with a regexp which matches a 8-bit character, so maybe Ruby should have given the same error before? Alternatively, I can revert if that is better?

My previous statement was incorrect.  The reason it worked before is that `\c` behavior in regexps was wrong and did not result in the 8-bit character it should have.  If you used a character resulting in a high bit, you did get the same error:

```
$ LANG=en_US.UTF-8 ruby -vce '/\M-a/'
ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-openbsd]
-e:1: too short escaped multibyte character: /\M-a/
-e:1: warning: possibly useless use of a literal in void context
```

You would also get an error if you created a regexp using a string instead of using a literal regexp:

```
$ LANG=en_US.UTF-8 ruby -ve '/#{s="\c\xff"}/'
ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-openbsd]
-e:1: warning: possibly useless use of a literal in void context
-e:1:in `<main>': invalid multibyte character (ArgumentError)
```

So I don't think anything is broken on UTF-8 (or other encodings).  Before, it should have raised an error and it didn't because the incorrect algorithm resulted in the wrong character.  Now it raises an error as it should.

----------------------------------------
Bug #14367: Wrong interpretation of backslash C in regexp literals
https://bugs.ruby-lang.org/issues/14367#change-91954

* Author: shyouhei (Shyouhei Urabe)
* Status: Closed
* Priority: Normal
* ruby -v: ruby 2.6.0dev (2018-01-16 trunk 61875) [x86_64-darwin15]
* Backport: 2.3: UNKNOWN, 2.4: UNKNOWN, 2.5: UNKNOWN
----------------------------------------
Following ruby code returns nil.

```sh
% LC_ALL=C ruby -ve 'p(/\c\xFF/ =~ "\c\xFF")'
ruby 2.6.0dev (2018-01-16 trunk 61875) [x86_64-darwin15]
nil
```

Is this intentional?



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