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Postings from May 2016
On Sun May 22 13:14:54 2016, wyant wrote:
> This is a bug report for perl from wyant@cpan.org,
> generated with the help of perlbug 1.40 running under perl 5.24.0.
>
>
> -----------------------------------------------------------------
> [Please describe your issue here]
>
> As I understand it, literal left curly brackets in regular expressions
> were deprecated in Perl 5.22, and with Perl 5.25.1 they produced a
> compile error. However, it appears that there is no warning (under
> 5.24.0) or error (under 5.25.1) for the following:
>
> /.{/
> /[x]{/
> /[xy]{/
> /\p{Latin}{/
>
> Compilation of these under 'use re debug' appears to show that the
> curlys are compiled as literals. Examples of this are appended. I note
> that /x(?:{)/ also produces no warning/exception, but I understand
> this
> to be an instance of the exception for leading curlys.
>
> Is all this a misunderstanding of the deprecation on my part? Or an
> obscure code path missed in the deprecation? If the former, please
> accept my apologies for wasting your time. And in either case, thank
> you
> very much for making Perl what it is today.
>
> Appended example:
>
> $ perl -c -Mre=debug -e '/.{/'
> Compiling REx ".{"
> Final program:
> 1: REG_ANY (2)
> 2: EXACT <{> (4)
> 4: END (0)
> anchored "{" at 1 (checking anchored) minlen 2
> -e syntax OK
> Freeing REx: ".{"
>
> $ # but
>
> $ perl -c -Mre=debug -e '/x{/'
> Compiling REx "x{"
> Unescaped left brace in regex is deprecated, passed through in regex;
> marked by <-- HERE in m/x{ <-- HERE / at -e line 1.
> Final program:
> 1: EXACT <x{> (3)
> 3: END (0)
> anchored "x{" at 0 (checking anchored isall) minlen 2
> -e syntax OK
> Freeing REx: "x{"
>
I can confirm your observations that no exceptions are thrown in these instances in perl 5.24.0. I can also confirm your observations re "perl -c -Mre=debug -e ...".
I am not a regex expert and didn't follow the discussion of this feature. But I suspect this may be a case where the error message is not sufficiently precise as to the error condition.
If we look at the source code we see this starting at line 13190 of 'regcomp.c':
#####
case '{':
/* Currently we don't care if the lbrace is at the start
* of a construct. This catches it in the middle of a
* literal string, or when it's the first thing after
* something like "\b" */
if (len || (p > RExC_start && isALPHA_A(*(p -1)))) {
RExC_parse = p + 1;
vFAIL("Unescaped left brace in regex is illegal");
}
/*FALLTHROUGH*/
default: /* A literal character */
#####
The term 'construct' is used (as both noun and verb) throughout the inline comments in this file but I didn't see a precise definition of its noun version. I'm also not entirely clear as to what 'literal string' and 'something like "\b"' mean. But I would hazard a guess that in the examples you cite, the characters preceding the unescaped left brace, i.e.,
#####
.
[x]
[xy]
\p{Latin}
#####
... because they are all regex-y things, disqualify these from being 'literal strings' and thus do not qualify as an error conditions.
Pinging our regex experts!
Thank you very much.
--
James E Keenan (jkeenan@cpan.org)
---
via perlbug: queue: perl5 status: new
https://rt.perl.org/Ticket/Display.html?id=128213
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