for lvalue_sub

[p5pRT]

Migrated from rt.perl.org#23790 (status was 'resolved')

Searchable as RT23790$

[p5pRT]

From @Abigail

Created by @Abigail

  #!/usr/bin/perl

  use strict;
  use warnings;

  my @​foo = qw /one two three/;
  sub foo () : lvalue {@​foo}

  print for foo;
  __END__
  Use of uninitialized value in print at /tmp/bug line 9.

However, I expect it to print "onetwothree" (which is does in 5.6.0).
If I remove the '​: lvalue', or change the print statement to
'print for my @​a = foo', it prints "onetwothree".

This bug occurs from 5.6.1 up to and including bleadperl.

Abigail

Perl Info

Flags:
    category=core
    severity=low

Site configuration information for perl v5.8.0:

Configured by camel at Mon Oct 28 01:28:45 CET 2002.

Summary of my perl5 (revision 5.0 version 8 subversion 0) configuration:
  Platform:
    osname=linux, osvers=2.4.18-bf2.4, archname=i686-linux-64int-ld
    uname='linux alexandra 2.4.18-bf2.4 #1 son apr 14 09:53:28 cest 2002 i686 unknown '
    config_args='-des -Uversiononly -Dmydomain=.abigail.nl -Dcf_email=camel@abigail.nl -Dperladmin=camel@abigail.nl -Doptimize=-g -Dusemorebits -Dusedevel -Dusenm=false -Dprefix=/opt/perl -Dcc=gcc'
    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=define use64bitall=undef uselongdouble=define
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='gcc', ccflags ='-DDEBUGGING -fno-strict-aliasing -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-g',
    cppflags='-DDEBUGGING -fno-strict-aliasing'
    ccversion='', gccversion='3.0.4', gccosandvers=''
    intsize=4, longsize=4, ptrsize=4, doublesize=8, byteorder=12345678
    d_longlong=define, longlongsize=8, d_longdbl=define, longdblsize=12
    ivtype='long long', ivsize=8, nvtype='long double', nvsize=12, Off_t='off_t', lseeksize=8
    alignbytes=4, prototype=define
  Linker and Libraries:
    ld='gcc', ldflags =' -L/usr/local/lib'
    libpth=/usr/local/lib /lib /usr/lib
    libs=-lnsl -ldl -lm -lc -lcrypt -lutil
    perllibs=-lnsl -ldl -lm -lc -lcrypt -lutil
    libc=/lib/libc-2.2.5.so, so=so, useshrplib=false, libperl=libperl.a
    gnulibc_version='2.2.5'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-rdynamic'
    cccdlflags='-fpic', lddlflags='-shared -L/usr/local/lib'

Locally applied patches:
    


@INC for perl v5.8.0:
    /home/abigail/Perl
    /opt/perl/lib/5.8.0/i686-linux-64int-ld
    /opt/perl/lib/5.8.0
    /opt/perl/lib/site_perl/5.8.0/i686-linux-64int-ld
    /opt/perl/lib/site_perl/5.8.0
    /opt/perl/lib/site_perl
    .


Environment for perl v5.8.0:
    HOME=/home/abigail
    LANG=C
    LANGUAGE (unset)
    LD_LIBRARY_PATH=/home/abigail/Lib:/usr/local/lib:/usr/lib:/lib:/usr/X11R6/lib
    LOGDIR (unset)
    PATH=/home/abigail/Bin:/opt/perl/bin:/usr/local/bin:/usr/local/X11/bin:/usr/bin:/bin:/usr/local/sbin:/usr/sbin:/sbin:/usr/X11R6/bin:/usr/games:/usr/share/texmf/bin:/opt/Acrobat/bin:/opt/java/blackdown/j2sdk1.3.1/bin:/usr/local/games/bin
    PERL5LIB=/home/abigail/Perl
    PERLDIR=/opt/perl
    PERL_BADLANG (unset)
    SHELL=/bin/bash

[p5pRT]

From kasei@cpan.org

padav is leaving an arrayref on the stack when it told to return an
lvalue. But in an argument list it should be a list, so we need to
expand it somewhere.

[p5pRT]

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

[p5pRT]

From voropaev.andrey@gmail.com

Created by voropaev.andrey@gmail.com

I know, that lvalue subs are experimental. So this is not really an issue, just
a thing that does not work as one would expect.

The code example

##########################################
my @​a;

sub canmod : lvalue { @​a; }
(canmod()) = qw(a b c);
print "a is ", join(', ', @​a), "\n";
print 'canmod gives', join(', ', canmod()), "\n";
foreach(canmod())
{
  print "In loop​: $_\n";
  $_ .= "ll";
}
print join(',', @​a), "\n";
##########################################

Produces

---------------------------------------------
a is a, b, c
canmod gives a, b, c
In loop​:
zsh​: segmentation fault (core dumped) perl try.pl
-----------------------------------------------

Perl Info

Flags:
    category=core
    severity=none

Site configuration information for perl 5.12.2:

Configured by Gentoo at Mon Oct 25 11:45:43 CEST 2010.

Summary of my perl5 (revision 5 version 12 subversion 2) configuration:
   
  Platform:
    osname=linux, osvers=2.6.34-gentoo-r11, archname=x86_64-linux
    uname='linux vandal 2.6.34-gentoo-r11 #2 mon oct 11 16:13:47 cest 2010 x86_64 amd athlon(tm) 64 processor 3200+ authenticamd gnulinux '
    config_args='-des -Duseshrplib -Darchname=x86_64-linux -Dcc=x86_64-pc-linux-gnu-gcc -Doptimize=-march=athlon64 -O2 -pipe -Dldflags=-Wl,-O1 -Wl,--as-needed -Dprefix=/usr -Dsiteprefix=/usr -Dvendorprefix=/usr -Dscriptdir=/usr/bin -Dprivlib=/usr/lib64/perl5/5.12.2 -Darchlib=/usr/lib64/perl5/5.12.2/x86_64-linux -Dsitelib=/usr/lib64/perl5/site_perl/5.12.2 -Dsitearch=/usr/lib64/perl5/site_perl/5.12.2/x86_64-linux -Dvendorlib=/usr/lib64/perl5/vendor_perl/5.12.2 -Dvendorarch=/usr/lib64/perl5/vendor_perl/5.12.2/x86_64-linux -Dman1dir=/usr/share/man/man1 -Dman3dir=/usr/share/man/man3 -Dsiteman1dir=/usr/share/man/man1 -Dsiteman3dir=/usr/share/man/man3 -Dvendorman1dir=/usr/share/man/man1 -Dvendorman3dir=/usr/share/man/man3 -Dman1ext=1 -Dman3ext=3pm -Dlibperl=libperl.so.5.12.2 -Dlocincpth=  -Duselargefiles -Dd_semctl_semun -Dcf_by=Gentoo -Dmyhostname=localhost -Dperladmin=root@localhost -Dinstallusrbinperl=n -Ud_csh -Uusenm -Di_ndbm -Di_gdbm -Di_db -DDEBUGGING=none -Dinc_version_list=
 5.12.1/x86_64-linux 5.12.1 5.12.0/x86_64-linux 5.12.0  -Dusrinc=/usr/include -Dlibpth=/usr/local/lib64 /lib64 /usr/lib64'
    hint=recommended, useposix=true, d_sigaction=define
    useithreads=undef, usemultiplicity=undef
    useperlio=define, d_sfio=undef, uselargefiles=define, usesocks=undef
    use64bitint=define, use64bitall=define, uselongdouble=undef
    usemymalloc=n, bincompat5005=undef
  Compiler:
    cc='x86_64-pc-linux-gnu-gcc', ccflags ='-fno-strict-aliasing -pipe -fstack-protector -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64',
    optimize='-march=athlon64 -O2 -pipe',
    cppflags='-fno-strict-aliasing -pipe -fstack-protector'
    ccversion='', gccversion='4.4.4', 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='x86_64-pc-linux-gnu-gcc', ldflags ='-Wl,-O1 -Wl,--as-needed -fstack-protector'
    libpth=/usr/local/lib64 /lib64 /usr/lib64
    libs=-lnsl -lgdbm -ldb -ldl -lm -lcrypt -lutil -lc -lgdbm_compat
    perllibs=-lnsl -ldl -lm -lcrypt -lutil -lc
    libc=/lib/libc-2.11.2.so, so=so, useshrplib=true, libperl=libperl.so.5.12.2
    gnulibc_version='2.11.2'
  Dynamic Linking:
    dlsrc=dl_dlopen.xs, dlext=so, d_dlsymun=undef, ccdlflags='-Wl,-E'
    cccdlflags='-fPIC', lddlflags='-shared -march=athlon64 -O2 -pipe -fstack-protector -Wl,-O1 -Wl,--as-needed'

Locally applied patches:
    0001-gentoo_MakeMaker-RUNPATH.diff
    0002-gentoo_config_over.diff
    0003-gentoo_cpan_definstalldirs.diff
    0004-gentoo_cpanplus_definstalldirs.diff
    0005-gentoo_create-libperl-soname.diff
    0006-gentoo_MakeMaker-delete_packlist.diff
    0007-fixes_8d66b3f9_h2hp_fix.diff


@INC for perl 5.12.2:
    /usr/lib64/perl5/site_perl/5.12.2/x86_64-linux
    /usr/lib64/perl5/site_perl/5.12.2
    /usr/lib64/perl5/vendor_perl/5.12.2/x86_64-linux
    /usr/lib64/perl5/vendor_perl/5.12.2
    /usr/lib64/perl5/5.12.2/x86_64-linux
    /usr/lib64/perl5/5.12.2
    /usr/lib64/perl5/site_perl
    /usr/lib64/perl5/vendor_perl
    .


Environment for perl 5.12.2:
    HOME=/home/andrei
    LANG (unset)
    LANGUAGE (unset)
    LC_CTYPE=en_US.UTF-8
    LD_LIBRARY_PATH (unset)
    LOGDIR (unset)
    PATH=/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/x86_64-pc-linux-gnu/gcc-bin/4.4.3:/usr/games/bin:/opt/Adobe/Reader8/bin:/opt/java/jdk1.6.0_03/bin:/opt/Adobe/Reader8/bin:/opt/java/jdk1.6.0_03/bin
    PERL_BADLANG (unset)
    SHELL=/bin/zsh

[p5pRT]

From kasei@cpan.org

Attached a fix for lvalue subs returning an array into the args of
another sub call or for loop.

I've modified leavesublv in that case to convert the returned arrayref
to a non-ref.

[p5pRT]

From kasei@cpan.org

0001-fix-for-23790.patch

From ba8f5d50c4a9a94867872ba5c341fa7e5b546e48 Mon Sep 17 00:00:00 2001
From: Marty Pauley <marty@martian.org>
Date: Sun, 24 Oct 2010 18:02:40 +0900
Subject: [PATCH] fix for #23790.

padav is leaving an arrayref on the stack when producing the return value for an
lvalue sub.  But when this is in an argument list it really should be a array,
not a ref.  So, in leavesublv I check for this case and expand the arrayref to
an array.
---
 pp_hot.c        |   23 +++++++++++++++++++++++
 t/op/sub_lval.t |   12 +++++++++---
 2 files changed, 32 insertions(+), 3 deletions(-)

diff --git a/pp_hot.c b/pp_hot.c
index 34542c2..2d6cba9 100644
--- a/pp_hot.c
+++ b/pp_hot.c
@@ -2598,6 +2598,29 @@ PP(pp_leavesublv)
 	if (gimme == G_SCALAR)
 	    goto temporise;
 	if (gimme == G_ARRAY) {
+	    mark = newsp + 1;
+	    /* We want an array here, but padav will have left us an arrayref for an lvalue,
+	     * so we need to expand it */
+	    if(SvTYPE(*mark) == SVt_PVAV) {
+		AV *const av = MUTABLE_AV(*mark);
+		const I32 maxarg = AvFILL(av) + 1;
+		(void)POPs; /* get rid of the array ref */
+		EXTEND(SP, maxarg);
+		if (SvRMAGICAL(av)) {
+		    U32 i;
+		    for (i=0; i < (U32)maxarg; i++) {
+			SV ** const svp = av_fetch(av, i, FALSE);
+			SP[i+1] = svp
+			    ? SvGMAGICAL(*svp) ? (mg_get(*svp), *svp) : *svp
+			    : &PL_sv_undef;
+		    }
+		}
+		else {
+		    Copy(AvARRAY(av), SP+1, maxarg, SV*);
+		}
+		SP += maxarg;
+		PUTBACK;
+	    }
 	    if (!CvLVALUE(cx->blk_sub.cv))
 		goto temporise_array;
 	    EXTEND_MORTAL(SP - newsp);
diff --git a/t/op/sub_lval.t b/t/op/sub_lval.t
index aedaba0..d0ba84a 100644
--- a/t/op/sub_lval.t
+++ b/t/op/sub_lval.t
@@ -3,7 +3,7 @@ BEGIN {
     @INC = '../lib';
     require './test.pl';
 }
-plan tests=>74;
+plan tests=>76;
 
 sub a : lvalue { my $a = 34; ${\(bless \$a)} }  # Return a temporary
 sub b : lvalue { ${\shift} }
@@ -527,8 +527,7 @@ TODO: {
     is($blah, 8, "yada");
 }
 
-TODO: {
-    local $TODO = "bug #23790";
+{ # bug #23790
     my @arr  = qw /one two three/;
     my $line = "zero";
     sub lval_array () : lvalue {@arr}
@@ -538,6 +537,13 @@ TODO: {
     }
 
     is($line, "zeroonetwothree");
+
+    sub trythislval { scalar(@_)."x".join "", @_ }
+    is(trythislval(lval_array()), "3xonetwothree");
+
+    sub changeme { $_[2] = "free" }
+    changeme(lval_array);
+    is("@arr", "one two free");
 }
 
 {
-- 
1.7.2.3

[p5pRT]

From @cpansprout

On Mon Nov 01 08​:46​:20 2010, maokt wrote​:

Attached a fix for lvalue subs returning an array into the args of
another sub call or for loop.

I've modified leavesublv in that case to convert the returned arrayref
to a non-ref.

Thank you. Applied as 91e34d8.

[p5pRT]

@cpansprout - Status changed from 'open' to 'resolved'

[p5pRT]

From @cpansprout

On Thu Oct 28 02​:23​:36 2010, voropaev.andrey@​gmail.com wrote​:

The code example

##########################################
my @​a;

sub canmod : lvalue { @​a; }
(canmod()) = qw(a b c);
print "a is ", join(', ', @​a), "\n";
print 'canmod gives', join(', ', canmod()), "\n";
foreach(canmod())
{
print "In loop​: $_\n";
$_ .= "ll";
}
print join(',', @​a), "\n";
##########################################

Produces

---------------------------------------------
a is a, b, c
canmod gives a, b, c
In loop​:
zsh​: segmentation fault (core dumped) perl try.pl
-----------------------------------------------

Thank you for the report. This is the same as bug #23790, which has just
been fixed by change 91e34d8.

[p5pRT]

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

[p5pRT]

@cpansprout - Status changed from 'open' to 'resolved'

[p5pRT]

From @cpansprout

On Thu Nov 04 00​:35​:16 2010, sprout wrote​:

On Mon Nov 01 08​:46​:20 2010, maokt wrote​:

Attached a fix for lvalue subs returning an array into the args of
another sub call or for loop.

I've modified leavesublv in that case to convert the returned arrayref
to a non-ref.

Thank you. Applied as 91e34d8.

For the record​: That patch only worked if the array were the first thing
returned, so it did not fix sub​:lvalue{ $x,@​x } sub​:lvalue{ @​x,@​y }, and
sub​:lvalue { %x }. I’ve found a more general way to fix it, which I’ve
applied as commit 40c94d1.