[perl #50430] Filter::Util::Call problem with $_

# New Ticket Created by  Zsban Ambrus 
# Please include the string:  [perl #50430]
# in the subject line of all future correspondence about this issue. 
# <URL: http://rt.perl.org/rt3/Ticket/Display.html?id=50430 >


This is a bug report for perl from ambrus@math.bme.hu,
generated with the help of perlbug 1.35 running under perl v5.8.8.


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[Please enter your report here]


This is a strange problem with Filter::Util::Call.  Here is a perl script
that installs a source filter that doesn't transform the code at all, then
follows a simple hello world using that filter.

use Filter::Util::Call;
BEGIN{ filter_add(sub{
        my $s = filter_read;
        my $t = $_;
        $_ = $t; # <---
        $s;
}); }
print "hello, world\n";

The above code works as expected: it prints hello world.

However, if I modify it by deleting the line with the arrow, I get this:

use Filter::Util::Call;
BEGIN{ filter_add(sub{
        my $s = filter_read;
        my $t = $_;
        $s;
}); }
print "hello, world\n";

This code does not work.  It exits with 0 exit code without printing
anything.  I can't see why they should be different, the line I deleted
shouldn't change the way the filter transforms the code.

I could reproduce this bug on both perl 5.10.0 linux-x86 and perl 5.8.8
linux-x86, both compiled from vanilla source.

I've first posted the bug at "http://www.perlmonks.com/?node_id=664944" --
see the replies there.

Thanks and keep up the good work,

Ambrus


[Please do not change anything below this line]
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---
Flags:
    category=library
    severity=medium
---
Site configuration information for perl v5.8.8:

Configured by Debian Project at Sun Nov  4 15:45:42 UTC 2007.

Summary of my perl5 (revision 5 version 8 subversion 8) configuration:
  Platform:
    osname=linux, osvers=2.6.22-3-amd64, archname=x86_64-linux-gnu-thread-multi
    uname='linux deneb 2.6.22-3-amd64 #1 smp thu oct 11 15:23:23 utc
2007 x86_64 gnulinux '
    config_args='-Dusethreads -Duselargefiles -Dccflags=-DDEBIAN
-Dcccdlflags=-fPIC -Darchname=x86_64-linux-gnu -Dprefix=/usr
-Dprivlib=/usr/share/perl/5.8 -Darchlib=/usr/lib/perl/5.8
-Dvendorprefix=/usr -Dvendorlib=/usr/share/perl5
-Dvendorarch=/usr/lib/perl5 -Dsiteprefix=/usr/local
-Dsitelib=/usr/local/share/perl/5.8.8
-Dsitearch=/usr/local/lib/perl/5.8.8 -Dman1dir=/usr/share/man/man1
-Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/local/man/man1
-Dsiteman3dir=/usr/local/man/man3 -Dman1ext=1 -Dman3ext=3perl
-Dpager=/usr/bin/sensible-pager -Uafs -Ud_csh -Uusesfio -Uusenm
-Duseshrplib -Dlibperl=libperl.so.5.8.8 -Dd_dosuid -des'
    hint=recommended, useposix=true, d_sigaction=define
    usethreads=define use5005threads=undef useithreads=define
usemultiplicity=define
    useperlio=define d_sfio=undef uselargefiles=define usesocks=undef
    use64bitint=define use64bitall=define uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='cc', ccflags ='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS
-DDEBIAN -fno-strict-aliasing -pipe -I/usr/local/include
-D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2',
    cppflags='-D_REENTRANT -D_GNU_SOURCE -DTHREADS_HAVE_PIDS -DDEBIAN
-fno-strict-aliasing -pipe -I/usr/local/include'
    ccversion='', gccversion='4.1.2 20061115 (prerelease) (Debian
4.1.1-21)', gccosandvers=''
    intsize=4, longsize=8, ptrsize=8, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=16
    ivtype='long', ivsize=8, nvtype='double', nvsize=8, Off_t='off_t',
lseeksize=8
    alignbytes=8, prototype=define
  Linker and Libraries:
    ld='cc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lgdbm -lgdbm_compat -ldb -ldl -lm -lpthread -lc -lcrypt
    perllibs=-ldl -lm -lpthread -lc -lcrypt
    libc=/lib/libc-2.3.6.so, so=so, useshrplib=true, libperl=libperl.so.5.8.8
    gnulibc_version='2.3.6'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:


---
@INC for perl v5.8.8:
    /etc/perl
    /usr/local/lib/perl/5.8.8
    /usr/local/share/perl/5.8.8
    /usr/lib/perl5
    /usr/share/perl5
    /usr/lib/perl/5.8
    /usr/share/perl/5.8
    /usr/local/lib/site_perl
    .

---
Environment for perl v5.8.8:
    HOME=/home/student/ambrus
    LANG=C
    LANGUAGE (unset)
    LC_CTYPE=hu_HU
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/home/student/ambrus/local/bin:/usr/local/bin:/usr/bin:/bin:/usr/games
    PERL_BADLANG (unset)
    SHELL=/bin/bash

• [perl #50430] Filter::Util::Call problem with $_ by Zsban Ambrus