[Bug libstdc++/102447] std::regex incorrectly accepts invalid bracket expression

["rs2740 at gmail dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102447

--- Comment #7 from TC <rs2740 at gmail dot com> ---
(In reply to Jonathan Wakely from comment #6)
> I have looked in detail (I have the 3rd, 4th and 5th editions here) but my
> brain started oozing out of my ears.
> 
> 15.10.2.15 NonemptyClassRanges and 15.10.2.16 NonemptyClassRangesNoDash are
> the relevant sections of the 1999 3rd edition. The former defines:
> 
>   The internal helper function CharacterRange takes two CharSet parameters
>   A and B and performs the following:
>   1. If A does not contain exactly one character or B does not contain
> exactly
>   one character then throw a SyntaxError exception.
> 
> And the latter has this note:
> 
>   Informative comments: ClassRanges can expand into single ClassAtoms and/or
>   ranges of two ClassAtoms separated by dashes. In the latter case the
>   ClassRanges includes all characters between the first ClassAtom and the
>   second ClassAtom, inclusive; an error occurs if either ClassAtom does not
>   represent a single character (for example, if one is \w) or if the first
>   ClassAtom's code point value is greater than the second ClassAtom's code
>   point value.
> 
> 
> 
> The ClassAtom \w does not contain exactly one character, so I think it's a
> syntax error.
> 
> The 3rd edition doesn't mention any legacy features of RegExp, but it does
> seem to require the strict behaviour.

I've looked at the 1999 spec now, and agree with your reading.