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Regex inconsistency with multiple PRUNE/SKIP/COMMIT #12853

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p5pRT opened this issue Mar 15, 2013 · 3 comments
Open

Regex inconsistency with multiple PRUNE/SKIP/COMMIT #12853

p5pRT opened this issue Mar 15, 2013 · 3 comments
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distro-All type-core type-regex

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@p5pRT
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p5pRT commented Mar 15, 2013

Migrated from rt.perl.org#117179 (status was 'open')

Searchable as RT117179$
@p5pRT
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p5pRT commented Mar 15, 2013

From ph10@hermes.cam.ac.uk

Created by ph10@hermes.cam.ac.uk

I have been testing combinations of (*SKIP), (*PRUNE), etc to determine if
there is any precedence when several of them are present. It seems that the
rule is that whichever one is backtracked onto first does its thing, and
earlier ones are ignored. But there is one exception. Consider these two
patterns when matched against "aaaaaac" (6 'a' characters plus 'c')​:

/aaaaa(*SKIP)b|a+c/
/aaaaa(*PRUNE)b|a+c/

The first matches "ac" and the second "aaaac", entirely as expected. However,
if the patterns are changed to

/aaaaa(*COMMIT)(*SKIP)b|a+c/
/aaaaa(*COMMIT)(*PRUNE)b|a+c/

the first still matches "ac", but the second now gives "no match". In all other
cases I have tried, such as putting (*PRUNE) in front of (*SKIP) or vice versa,
and including tests with (*THEN), the insertion of the first verb makes no
difference, which is what I would expect if the rule is "first backtracked onto
is activated".

Here is some evidence of these effects​:

$ perl -e 'print (("aaaaaac" =~ /aaaaa(*SKIP)b|a+c/)? "$&\n"​:"no match\n");'
ac
$ perl -e 'print (("aaaaaac" =~ /aaaaa(*PRUNE)b|a+c/)? "$&\n"​:"no match\n");'
aaaac
$ perl -e 'print (("aaaaaac" =~ /aaaaa(*COMMIT)(*SKIP)b|a+c/)? "$&\n"​:"no match\n");'
ac
$ perl -e 'print (("aaaaaac" =~ /aaaaa(*COMMIT)(*PRUNE)b|a+c/)? "$&\n"​:"no match\n");'
no match
$

Perl Info 

Flags:
    category=core
    severity=low

Site configuration information for perl 5.16.2:

Configured by nobody at Sat Feb  2 15:24:52 CET 2013.

Summary of my perl5 (revision 5 version 16 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=3.7.4-1-arch, archname=i686-linux-thread-multi
    uname='linux flo32 3.7.4-1-arch #1 smp preempt mon jan 21 23:05:29 cet 2013 i686 gnulinux '
    config_args='-des -Dusethreads -Duseshrplib -Doptimize=-march=i686 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2 -Dprefix=/usr -Dvendorprefix=/usr -Dprivlib=/usr/share/perl5/core_perl -Darchlib=/usr/lib/perl5/core_perl -Dsitelib=/usr/share/perl5/site_perl -Dsitearch=/usr/lib/perl5/site_perl -Dvendorlib=/usr/share/perl5/vendor_perl -Dvendorarch=/usr/lib/perl5/vendor_perl -Dscriptdir=/usr/bin/core_perl -Dsitescript=/usr/bin/site_perl -Dvendorscript=/usr/bin/vendor_perl -Dinc_version_list=none -Dman1ext=1perl -Dman3ext=3perl -Dlddlflags=-shared -Wl,-O1,--sort-common,--as-needed,-z,relro -Dldflags=-Wl,-O1,--sort-common,--as-needed,-z,relro'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=define, usemultiplicity=define
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=undef, use64bitall=undef, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-march=i686 -mtune=generic -O2 -pipe -fstack-protector --param=ssp-buffer-size=4 -D_FORTIFY_SOURCE=2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.7.2', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long', ivsize=4, nvtype='double', nvsize=8, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='cc', ldflags ='-Wl,-O1,--sort-common,--as-needed,-z,relro -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lpthread -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lpthread -lc
    libc=/lib/libc-2.17.so, so=so, useshrplib=true, libperl=libperl.so
    gnulibc_version='2.17'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E -Wl,-rpath,/usr/lib/perl5/core_perl/CORE'
    cccdlflags='-fPIC', lddlflags='-shared -Wl,-O1,--sort-common,--as-needed,-z,relro -L/usr/local/lib -fstack-protector'

Locally applied patches:
    


@INC for perl 5.16.2:
    /usr/lib/perl5/site_perl
    /usr/share/perl5/site_perl
    /usr/lib/perl5/vendor_perl
    /usr/share/perl5/vendor_perl
    /usr/lib/perl5/core_perl
    /usr/share/perl5/core_perl
    .


Environment for perl 5.16.2:
    HOME=/home/ph10
    LANG=en_GB
    LANGUAGE (unset)
    LC_ALL=C
    LC_COLLATE=C
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/ph10/bin:/usr/local/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/bin/vendor_perl:/usr/bin/core_perl:.
    PERL_BADLANG (unset)
    SHELL=/bin/bash

@p5pRT
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p5pRT commented Mar 17, 2013

From @ikegami

On Fri, Mar 15, 2013 at 7​:18 AM, Philip Hazel <perlbug-followup@​perl.org>wrote​:

# New Ticket Created by Philip Hazel
# Please include the string​: [perl #117179]
# in the subject line of all future correspondence about this issue.
# <URL​: https://rt-archive.perl.org/perl5/Ticket/Display.html?id=117179 >

Cc​: nobody
Subject​: Regex​: COMMIT+SKIP differs from COMMIT+PRUNE
Message-Id​: <5.16.2_19279_1363344286@​quercite>
Reply-To​: ph10@​hermes.cam.ac.uk
To​: perlbug@​perl.org
From​: ph10@​hermes.cam.ac.uk

This is a bug report for perl from ph10@​hermes.cam.ac.uk,
generated with the help of perlbug 1.39 running under perl 5.16.2.

-----------------------------------------------------------------
[Please describe your issue here]

I have been testing combinations of (*SKIP), (*PRUNE), etc to determine if
there is any precedence when several of them are present. It seems that the
rule is that whichever one is backtracked onto first does its thing, and
earlier ones are ignored. But there is one exception. Consider these two
patterns when matched against "aaaaaac" (6 'a' characters plus 'c')​:

/aaaaa(*SKIP)b|a+c/
/aaaaa(*PRUNE)b|a+c/

The first matches "ac" and the second "aaaac", entirely as expected.
However,
if the patterns are changed to

/aaaaa(*COMMIT)(*SKIP)b|a+c/
/aaaaa(*COMMIT)(*PRUNE)b|a+c/

the first still matches "ac", but the second now gives "no match". In all
other
cases I have tried, such as putting (*PRUNE) in front of (*SKIP) or vice
versa,
and including tests with (*THEN), the insertion of the first verb makes no
difference, which is what I would expect if the rule is "first backtracked
onto
is activated".

(*COMMIT)'s or (*PRUNE)'s behaviour differs from their documentation.
According to (*COMMIT) 's documentation, it should do its thing "when
backtracked into", but that can't happens when (*PRUNE) comes right after
because "no further backtracking will take place" after backtracking into
(*PRUNE).

@p5pRT
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p5pRT commented Mar 17, 2013

The RT System itself - Status changed from 'new' to 'open'

@xenu xenu removed the Severity Low label Dec 29, 2021
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