From @mauke

Created by @mauke

The following programs should all produce the same output​:

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do { local $/ = <STDIN> }'
[a
b
c
]

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do { local $/ = do { <STDIN> } }'
[a
]

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do { local $/ = (0, <STDIN>) }'
[a
]

I think the first one is broken.

Flags:
    category=core
    severity=low

This perlbug was built using Perl 5.12.1 - Thu Jun  3 20:09:15 CEST 2010
It is being executed now by  Perl 5.18.1 - Tue Aug 13 07:08:47 CEST 2013.

Site configuration information for perl 5.18.1:

Configured by mauke at Tue Aug 13 07:08:47 CEST 2013.

Summary of my perl5 (revision 5 version 18 subversion 1) configuration:
   
  Platform:
    osname=linux, osvers=3.5.7-gentoo, archname=i686-linux
    uname='linux nora 3.5.7-gentoo #5 preempt sat jan 26 16:46:10 cet 2013 i686 amd athlon(tm) 64 processor 3200+ authenticamd gnulinux '
    config_args=''
    hint=recommended, useposix=true, d_sigaction=define
    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-strict-aliasing -pipe -fstack-protector -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-O2 -flto',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector -I/usr/local/include'
    ccversion='', gccversion='4.8.1', 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 ='-O2 -flto -fstack-protector -L/usr/local/lib'
    libpth=/usr/local/lib /lib/../lib /usr/lib/../lib /lib /usr/lib
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.15.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.15'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -O2 -flto -L/usr/local/lib -fstack-protector'

Locally applied patches:
    SAVEARGV0 - disable magic open in <ARGV>


@INC for perl 5.18.1:
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.1/i686-linux
    /home/mauke/usr/local/lib/perl5/site_perl/5.18.1
    /home/mauke/usr/local/lib/perl5/5.18.1/i686-linux
    /home/mauke/usr/local/lib/perl5/5.18.1
    .


Environment for perl 5.18.1:
    HOME=/home/mauke
    LANG=en_US.UTF-8
    LANGUAGE (unset)
    LC_COLLATE=POSIX
    LD_LIBRARY_PATH=/home/mauke/usr/local/lib
    LOGDIR (unset)
    PATH=/home/mauke/usr/perlbrew/bin:/home/mauke/usr/local/bin:/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/i686-pc-linux-gnu/gcc-bin/4.6.3:/opt/sun-jdk-1.4.2.13/bin:/opt/sun-jdk-1.4.2.13/jre/bin:/opt/sun-jdk-1.4.2.13/jre/javaws:/opt/dmd/bin:/usr/games/bin
    PERLBREW_BASHRC_VERSION=0.43
    PERLBREW_HOME=/home/mauke/.perlbrew
    PERLBREW_PATH=/home/mauke/usr/perlbrew/bin
    PERLBREW_ROOT=/home/mauke/usr/perlbrew
    PERLBREW_VERSION=0.27
    PERL_BADLANG (unset)
    PERL_UNICODE=SAL
    SHELL=/bin/bash

From @cpansprout

On Tue Aug 27 13​:12​:01 2013, mauke- wrote​:

The following programs should all produce the same output​:

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do {
local $/ = <STDIN> }'
[a
b
c
]

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do {
local $/ = do { <STDIN> } }'
[a
]

% perl -e 'print "a\nb\nc\n"' | perl -we 'print "[$_]\n" for do {
local $/ = (0, <STDIN>) }'
[a
]

I think the first one is broken.

A readline optimisation is causing the order of evaluation to change,
making the ‘local $/’ get executed too soon​:

Notice how the LVINTRO line is number 3 while readline is number 5​:

$ ./perl -Ilib -MO=Concise -e ' local $/ = <foo> '
6 <@​> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 1 -e​:1) v​:{ ->3
- <1> null vKS/2 ->6
- <1> ex-rv2sv sKRM*/129 ->4
3 <#> gvsv[*/] s/LVINTRO ->4
5 <1> readline[t3] sKS/1 ->6
4 <#> gv[*foo] s ->5
-e syntax OK

Here the numbers are 5 and 4, so the execution order is different​:

$ ./perl -Ilib -MO=Concise -e ' local $/ = do { <foo> } '
7 <@​> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 2 -e​:1) v​:{ ->3
6 <2> sassign vKS/2 ->7
- <1> null sK*/1 ->5
- <@​> scope sK ->-
- <0> ex-nextstate v ->3
4 <1> readline[t3] sK/1 ->5
3 <#> gv[*foo] s ->4
- <1> ex-rv2sv sKRM*/129 ->6
5 <#> gvsv[*/] s/LVINTRO ->6
-e syntax OK

--

Father Chrysostomos

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

From @mauke

On Di. 27. Aug. 2013, 14​:39​:39, sprout wrote​:

A readline optimisation is causing the order of evaluation to change,
making the ‘local $/’ get executed too soon​:

Notice how the LVINTRO line is number 3 while readline is number 5​:

$ ./perl -Ilib -MO=Concise -e ' local $/ = <foo> '
6 <@​> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 1 -e​:1) v​:{ ->3
- <1> null vKS/2 ->6
- <1> ex-rv2sv sKRM*/129 ->4
3 <#> gvsv[*/] s/LVINTRO ->4
5 <1> readline[t3] sKS/1 ->6
4 <#> gv[*foo] s ->5
-e syntax OK

Here the numbers are 5 and 4, so the execution order is different​:

$ ./perl -Ilib -MO=Concise -e ' local $/ = do { <foo> } '
7 <@​> leave[1 ref] vKP/REFC ->(end)
1 <0> enter ->2
2 <;> nextstate(main 2 -e​:1) v​:{ ->3
6 <2> sassign vKS/2 ->7
- <1> null sK*/1 ->5
- <@​> scope sK ->-
- <0> ex-nextstate v ->3
4 <1> readline[t3] sK/1 ->5
3 <#> gv[*foo] s ->4
- <1> ex-rv2sv sKRM*/129 ->6
5 <#> gvsv[*/] s/LVINTRO ->6
-e syntax OK

That optimization seems to be blatantly invalid. :-)

% cat try.pl
#!/usr/bin/perl
use strict;
use warnings;

{
  package Ohai;

  sub TIEHANDLE {
  my $class = shift;
  bless {@​_}, $class
  }

  sub READLINE {
  my $self = shift;
  $self->{readline}()
  }
}

our $xy = 42;

tie *HDL, 'Ohai', (
  readline => sub {
  print "the value of \$xy is [$xy]\n";
  qw(a b c)
  },
);

{ local $xy = do { <HDL> }; }
{ local $xy = <HDL>; }
__END__

% perl try.pl
the value of $xy is [42]
Use of uninitialized value $xy in concatenation (.) or string at try.pl
line 23.
the value of $xy is []