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[perl #59168] 5.8.x: regexp bug with (?!)
# New Ticket Created by Father Chrysostomos
# Please include the string: [perl #59168]
# in the subject line of all future correspondence about this issue.
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=59168 >
perl 5.8.9-to-be (34300) has an elusive regexp bug involving
backtracking, negative look-aheads and back-references. Look at the
output from this program, with 5.8.8 (same in 5.10 and blead [34308]),
and with maint:
use Data::Dumper;
baaabaac =~ /(.*?)a(?!(a+)b\2(?{print "$-[0] $2\n"})c)/;
print Dumper [$&,$1];
print Dumper [@-[0,1]];
$ perl5.8.8 prog
0 aa
0 a
$VAR1 = [
'baa',
'ba',
];
$VAR1 = [
'0',
'0',
];
$ /opt/maint/bin/perl prog
0 aa
1 aa
$VAR1 = [
'a',
'',
];
$VAR1 = [
'2',
'2',
];
It appears that, after the first attempt at matching the contents of
(?!...) succeeds (causing a failure), it doesn’t backtrack and try
alternative ways of matching the (.*?). Instead it reverses all the
way back and tries matching the entire regexp from char 1.
The output from -Mre=debug and perlbug -d follows:
Compiling REx `(.*?)a(?!(a+)b\2c)'
size 27 Got 220 bytes for offset annotations.
first at 4
synthetic stclass "ANYOF[\0-\11\13-\377{unicode_all}]".
1: OPEN1(3)
3: MINMOD(4)
4: STAR(6)
5: REG_ANY(0)
6: CLOSE1(8)
8: EXACT <a>(10)
10: UNLESSM[-0](27)
12: OPEN2(14)
14: PLUS(17)
15: EXACT <a>(0)
17: CLOSE2(19)
19: EXACT <b>(21)
21: REF2(23)
23: EXACT <c>(25)
25: SUCCEED(0)
26: TAIL(27)
27: END(0)
floating "a" at 0..2147483647 (checking floating) stclass "ANYOF[\0-
\11\13-\377{unicode_all}]" minlen 1
Offsets: [27]
1[1] 0[0] 4[1] 3[1] 2[1] 5[1] 0[0] 6[1] 0[0] 10[8] 0[0] 10[1] 0[0]
12[1] 11[1] 0[0] 13[1] 0[0] 14[1] 0[0] 15[2] 0[0] 17[1] 0[0] 17[0]
17[0] 19[0]
Guessing start of match, REx "(.*?)a(?!(a+)b\2c)" against "baaabaac"...
Found floating substr "a" at offset 1...
Does not contradict STCLASS...
Guessed: match at offset 0
Matching REx "(.*?)a(?!(a+)b\2c)" against "baaabaac"
Matching stclass "ANYOF[\0-\11\13-\377{unicode_all}]" against "baaabaac"
Setting an EVAL scope, savestack=3
0 <> <baaabaac> | 1: OPEN1
0 <> <baaabaac> | 3: MINMOD
0 <> <baaabaac> | 4: STAR
Setting an EVAL scope, savestack=3
REG_ANY can match 1 times out of 1...
1 <b> <aaabaac> | 6: CLOSE1
1 <b> <aaabaac> | 8: EXACT <a>
2 <ba> <aabaac> | 10: UNLESSM[-0]
2 <ba> <aabaac> | 12: OPEN2
2 <ba> <aabaac> | 14: PLUS
EXACT <a> can match 2 times out of
2147483647...
Setting an EVAL scope, savestack=3
4 <baaa> <baac> | 17: CLOSE2
4 <baaa> <baac> | 19: EXACT <b>
5 <baaab> <aac> | 21: REF2
7 <baaabaa> <c> | 23: EXACT <c>
8 <baaabaac> <> | 25: SUCCEED
could match...
failed...
REG_ANY can match 0 times out of 1...
failed...
Setting an EVAL scope, savestack=3
1 <b> <aaabaac> | 1: OPEN1
1 <b> <aaabaac> | 3: MINMOD
1 <b> <aaabaac> | 4: STAR
Setting an EVAL scope, savestack=3
1 <b> <aaabaac> | 6: CLOSE1
1 <b> <aaabaac> | 8: EXACT <a>
2 <ba> <aabaac> | 10: UNLESSM[-0]
2 <ba> <aabaac> | 12: OPEN2
2 <ba> <aabaac> | 14: PLUS
EXACT <a> can match 2 times out of
2147483647...
Setting an EVAL scope, savestack=3
4 <baaa> <baac> | 17: CLOSE2
4 <baaa> <baac> | 19: EXACT <b>
5 <baaab> <aac> | 21: REF2
7 <baaabaa> <c> | 23: EXACT <c>
8 <baaabaac> <> | 25: SUCCEED
could match...
failed...
REG_ANY can match 0 times out of 1...
failed...
Setting an EVAL scope, savestack=3
2 <ba> <aabaac> | 1: OPEN1
2 <ba> <aabaac> | 3: MINMOD
2 <ba> <aabaac> | 4: STAR
Setting an EVAL scope, savestack=3
2 <ba> <aabaac> | 6: CLOSE1
2 <ba> <aabaac> | 8: EXACT <a>
3 <baa> <abaac> | 10: UNLESSM[-0]
3 <baa> <abaac> | 12: OPEN2
3 <baa> <abaac> | 14: PLUS
EXACT <a> can match 1 times out of
2147483647...
Setting an EVAL scope, savestack=3
4 <baaa> <baac> | 17: CLOSE2
4 <baaa> <baac> | 19: EXACT <b>
5 <baaab> <aac> | 21: REF2
6 <baaaba> <ac> | 23: EXACT <c>
failed...
failed...
3 <baa> <abaac> | 27: END
Match successful!
Freeing REx: `"(.*?)a(?!(a+)b\\2c)"'
---
Flags:
category=core
severity=high
---
Site configuration information for perl v5.8.8:
Configured by sprout at Wed Sep 17 21:26:05 PDT 2008.
Summary of my perl5 (revision 5 version 8 subversion 8 patch 34376)
configuration:
Platform:
osname=darwin, osvers=9.4.0, archname=darwin-2level
uname='darwin pint.local 9.4.0 darwin kernel version 9.4.0: mon
jun 9 19:30:53 pdt 2008; root:xnu-1228.5.20~1release_i386 i386 '
config_args='-de -Dprefix=/opt/maint/'
hint=recommended, useposix=true, d_sigaction=define
usethreads=undef use5005threads=undef useithreads=undef
usemultiplicity=undef
useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
use64bitint=undef use64bitall=undef uselongdouble=undef
usemymalloc=n, bincompat5005=undef
Compiler:
cc='cc', ccflags ='-fno-common -DPERL_DARWIN -no-cpp-precomp -fno-
strict-aliasing -pipe -I/usr/local/include',
optimize='-O3',
cppflags='-no-cpp-precomp -fno-common -DPERL_DARWIN -no-cpp-
precomp -fno-strict-aliasing -pipe -I/usr/local/include'
ccversion='', gccversion='4.0.1 (Apple Inc. build 5484)',
gccosandvers=''
intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=1234
d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
ivtype='long', ivsize=4, nvtype='double', nvsize=8,
Off_t='off_t', lseeksize=8
alignbytes=8, prototype=define
Linker and Libraries:
ld='env MACOSX_DEPLOYMENT_TARGET=10.3 cc', ldflags =' -L/usr/
local/lib'
libpth=/usr/local/lib /usr/lib
libs=-ldbm -ldl -lm -lutil -lc
perllibs=-ldl -lm -lutil -lc
libc=/usr/lib/libc.dylib, so=dylib, useshrplib=false,
libperl=libperl.a
gnulibc_version=''
Dynamic Linking:
dlsrc=dl_dlopen.xs, dlext=bundle, d_dlsymun=undef, ccdlflags=' '
cccdlflags=' ', lddlflags=' -bundle -undefined dynamic_lookup -L/
usr/local/lib'
Locally applied patches:
MAINT34300
---
@INC for perl v5.8.8:
/opt/maint/lib/perl5/5.8.8/darwin-2level
/opt/maint/lib/perl5/5.8.8
/opt/maint/lib/perl5/site_perl/5.8.8/darwin-2level
/opt/maint/lib/perl5/site_perl/5.8.8
.
---
Environment for perl v5.8.8:
DYLD_LIBRARY_PATH (unset)
HOME=/Users/sprout
LANG=en_US.UTF-8
LANGUAGE (unset)
LD_LIBRARY_PATH (unset)
LOGDIR (unset)
PATH=/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin:/usr/X11/bin:/
usr/local/bin
PERL_BADLANG (unset)
SHELL=/bin/bash
- Follow-Ups from:
-
Nicholas Clark <nick@ccl4.org>
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