Bug#732715: liblist-moreutils-perl: "Attempt to free unreferenced scalar" in some use cases of List::MoreUtils::part

[Christoph Biedl]

Package: liblist-moreutils-perl
Version: 0.33-1+b2
Severity: normal

Dear Maintainer,

This is quite weird. If the code used in `part`

* is built using given..when
* does a return after a match on the first value of the list

the code will result in the dreaded "Attempt to free unreferenced scalar"
message. Reproducer (tested on amd64 and i386):

{{{
#!/usr/bin/perl

use 5.010;
use List::MoreUtils;

my @files = (
    'foo',
    'bar',
);

my @groups = List::MoreUtils::part (
    sub {
        given ($_) {
            when ('foo') {
                return 0;   # this return is evil
            }
            default {
                return 1;   # this one does no harm
            }
        }
    },
    @files,
);
}}}

Output:
{{{
given is experimental at reproducer line 13.
when is experimental at reproducer line 14.
Attempt to free unreferenced scalar: SV 0x1c1ae98, Perl interpreter: 0x1c18010.
}}}

There is more than one workaround: Omit the "return" keyword.
Rewriting the code to "return" outside the given..when block does
the trick, too. The pure Perl implementation does the right thing,
too.

As said before, the message is triggered by the way the code block
is left for the first list element of the list processed, in other
words, this one

{{{
    when ('bar') {
        1;
    }
    default {
        return 0;
    }
}}}

is affected, too.

So I think somebody should take a look into that. I'm concerned the
observation is just a symptom of a bigger problem like data
corruption.


-- System Information:
Debian Release: jessie/sid
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: amd64 (x86_64)

Kernel: Linux 3.10.24 (SMP w/4 CPU cores; PREEMPT)
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)
Shell: /bin/sh linked to /bin/dash

Versions of packages liblist-moreutils-perl depends on:
ii  libc6                       2.17-97
ii  perl                        5.18.1-5
ii  perl-base [perlapi-5.18.1]  5.18.1-5

liblist-moreutils-perl recommends no packages.

liblist-moreutils-perl suggests no packages.

-- no debconf information

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