[perl #132367] Allow variable length lookbehind for folded

# New Ticket Created by  karl williamson 
# Please include the string:  [perl #132367]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=132367 >


This is a bug report for perl from khw@cpan.org,
generated with the help of perlbug 1.40 running under perl 5.27.6.


-----------------------------------------------------------------
See the thread beginning with
http://nntp.perl.org/group/perl.perl5.porters/245323
Some negative lookbehind assertions were inadvertently broken by moving
to Unicode folding rules.  It should be fairly easy to fix this for 
these limited cases.



[Please do not change anything below this line]
-----------------------------------------------------------------
---
Flags:
     category=core
     severity=medium
---
Site configuration information for perl 5.27.6:

Configured by khw at Sat Oct 28 12:44:02 MDT 2017.

Summary of my perl5 (revision 5 version 27 subversion 6) configuration:
   Derived from: 72e3589821b9340dca575b7367c601d819d273f9
   Platform:
     osname=linux
     osvers=4.10.0-37-generic
     archname=x86_64-linux-thread-multi-ld
     uname='linux khw 4.10.0-37-generic #41-ubuntu smp fri oct 6 
20:20:37 utc 2017 x86_64 x86_64 x86_64 gnulinux '
     config_args='-des -Uversiononly -Dprefix=/home/khw/devel -Dusedevel 
-A'optimize=-ggdb3' -A'optimize=-O0' -Accflags='-Wno-c++11-compat' 
-Accflags='-DPERL_BOOL_AS_CHAR' -Accflags='-Wno-deprecated' 
-Accflags='-DPERL_EXTERNAL_GLOB' -Dman1dir=none -Dman3dir=none -Dcc=g++ 
-DDEBUGGING -Dusemorebits -Dusecbacktrace -Dusethreads'
     hint=recommended
     useposix=true
     d_sigaction=define
     useithreads=define
     usemultiplicity=define
     use64bitint=define
     use64bitall=define
     uselongdouble=define
     usemymalloc=n
     default_inc_excludes_dot=define
     bincompat5005=undef
   Compiler:
     cc='g++'
     ccflags ='-D_REENTRANT -D_GNU_SOURCE -Wno-c++11-compat 
-DPERL_BOOL_AS_CHAR -Wno-deprecated -DPERL_EXTERNAL_GLOB -fwrapv 
-DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong 
-I/usr/local/include -DUSE_C_BACKTRACE -g -D_LARGEFILE_SOURCE 
-D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2'
     optimize='-O2 -ggdb3 -O0'
     cppflags='-D_REENTRANT -D_GNU_SOURCE -Wno-c++11-compat 
-DPERL_BOOL_AS_CHAR -Wno-deprecated -DPERL_EXTERNAL_GLOB -fwrapv 
-DDEBUGGING -fno-strict-aliasing -pipe -fstack-protector-strong 
-I/usr/local/include'
     ccversion=''
     gccversion='6.3.0 20170406'
     gccosandvers=''
     intsize=4
     longsize=8
     ptrsize=8
     doublesize=8
     byteorder=12345678
     doublekind=3
     d_longlong=define
     longlongsize=8
     d_longdbl=define
     longdblsize=16
     longdblkind=3
     ivtype='long'
     ivsize=8
     nvtype='long double'
     nvsize=16
     Off_t='off_t'
     lseeksize=8
     alignbytes=16
     prototype=define
   Linker and Libraries:
     ld='g++'
     ldflags =' -fstack-protector-strong -L/usr/local/lib'
     libpth=/usr/include/c++/6 /usr/include/x86_64-linux-gnu/c++/6 
/usr/include/c++/6/backward /usr/local/lib 
/usr/lib/gcc/x86_64-linux-gnu/6/include-fixed 
/usr/include/x86_64-linux-gnu /usr/lib /lib/x86_64-linux-gnu /lib/../lib 
/usr/lib/x86_64-linux-gnu /usr/lib/../lib /lib
     libs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
     perllibs=-lpthread -lnsl -ldl -lm -lcrypt -lutil -lc
     libc=libc-2.24.so
     so=so
     useshrplib=false
     libperl=libperl.a
     gnulibc_version='2.24'
   Dynamic Linking:
     dlsrc=dl_dlopen.xs
     dlext=so
     d_dlsymun=undef
     ccdlflags='-Wl,-E'
     cccdlflags='-fPIC'
     lddlflags='-shared -O2 -ggdb3 -O0 -L/usr/local/lib 
-fstack-protector-strong'

Locally applied patches:
     uncommitted-changes

---
@INC for perl 5.27.6:
     /home/khw/perl/neglookbehind/lib
     /home/khw/perl/neglookbehind/t
     /home/khw/devel/lib/perl5/site_perl/5.27.6/x86_64-linux-thread-multi-ld
     /home/khw/devel/lib/perl5/site_perl/5.27.6
     /home/khw/devel/lib/perl5/5.27.6/x86_64-linux-thread-multi-ld
     /home/khw/devel/lib/perl5/5.27.6
     /home/khw/devel/lib/perl5/site_perl/5.26.0
     /home/khw/devel/lib/perl5/site_perl

---
Environment for perl 5.27.6:
     HOME=/home/khw
     LANG=en_US.UTF-8
     LANGUAGE=en_US
     LD_LIBRARY_PATH (unset)
     LOGDIR (unset)
 
PATH=/usr/lib/ccache:/home/khw/bin:/home/khw/perl5/perlbrew/bin:/home/khw/print/bin:/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/usr/games:/usr/local/games:/home/khw/iands/www:/home/khw/cxoffice/bin
     PERL5OPT=-w
     PERL_BADLANG (unset)
     PERL_DIFF_TOOL=wgdiff
     PERL_POD_PEDANTIC=1
     SHELL=/bin/ksh

• [perl #132367] Allow variable length lookbehind for folded by karl williamson