Bug #16145: regexp match error if mixing /i, character classes, and utf8

• Status: Open
• Assignee: -
• Target version: -
• Backport: 2.5: UNKNOWN, 2.6: UNKNOWN
• Tags: regexp

[zenspider (Ryan Davis)]

(reported on behalf of [e-mail] -- there appears to be an error in registration or login):

See: ruby-talk @ X-Mail-Count: 440336

2.6.3 :049 > 'SHOP' =~ /[xo]/i
=> 2
2.6.3 :050 > 'CAFÉ' =~ /[é]/i
=> 3
2.6.3 :051 > 'CAFÉ' =~ /[xé]/i
=> nil
2.6.3 :052 > 'CAFÉ' =~ /[xÉ]/i
=> 3

Expected result:
2.6.3 :051 > 'CAFÉ' =~ /[xé]/i
=> 3

I tested it on random regex online pages.

It does not match on https://regex101.com/

It matches on:

https://regexr.com/
https://www.regextester.com/
https://www.freeformatter.com/regex-tester.html

(Ignore case turned on).

The reason I suppose it’s more like a bug than a feature is the fact that /[é]/i matches 'CAFÉ'. If the //i didn’t work for UTF-8 characters then the /[é]/i wouldn’t match it either. For example, [é] does not match 'CAFÉ' on https://regex101.com/

I could not find a page or a system that behaves the same way as Ruby does. For example, it matches in PostgreSQL 10 (under FreeBSD 12) too:

select 'CAFÉ'~ '[xé]';

?column?

f
(1 row)

select 'CAFÉ' ~* '[xé]';

?column?

t
(1 row)

Tested it in IRB on macOS and FreeBSD.

$ uname -a && ruby -v && locale
Darwin xxx 18.7.0 Darwin Kernel Version 18.7.0: Thu Jun 20 18:42:21 PDT 2019; root:xnu-4903.270.47~4/RELEASE_X86_64 x86_64
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-darwin18]
LANG="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_CTYPE="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_ALL="en_US.UTF-8"

$ uname -a && ruby -v && locale
FreeBSD xxx 12.0-RELEASE-p9 FreeBSD 12.0-RELEASE-p9 GENERIC amd64
ruby 2.6.3p62 (2019-04-16 revision 67580) [x86_64-freebsd12.0]
LANG=en_US.UTF-8
LC_CTYPE="en_US.UTF-8"
LC_COLLATE="en_US.UTF-8"
LC_TIME="en_US.UTF-8"
LC_NUMERIC="en_US.UTF-8"
LC_MONETARY="en_US.UTF-8"
LC_MESSAGES="en_US.UTF-8"
LC_ALL=en_US.UTF-8

I installed Ruby with RVM.

[duerst (Martin Dürst)]

Definitely a bug. Confirmed on master (ruby -v
ruby 2.7.0dev (2019-07-06T03:43:38Z trunk f296c260ef) [x86_64-cygwin])

"CAFÉ" =~ /x|é/i
works. So that may be an alternative until this is fixed. It may also give some hints on where the bug comes from. My current guess is that single-character character classes get reduced to just the actual character, so that's why they work.

[sancheta867 (Steven Ancheta)]

Confirmed that it's still happening on ruby -v ruby 3.2.2 (2023-03-30 revision e51014f9c0) [arm64-darwin23]

irb(main):001:0> 'CAFÉ' =~ /[xé]/i
=> nil
irb(main):002:0> "CAFÉ" =~ /x|é/i
=> 3

[zenspider (Ryan Davis)]

@duerst (Martin Dürst) I don't think your intuition about the character classes is correct:

"CAFÉ" =~ /[a]/i
# => 1

[duerst (Martin Dürst)]

@zenspider (Ryan Davis) I said that single-character character classes get reduced to just the actual character. So that would mean that your "CAFÉ" =~ /[a]/i gets reduced to "CAFÉ" =~ /a/i, and therefore works. That of course does not prove my guess, but it also doesn't disprove it. We'd need some other examples to test this further.