Perl, warn not working after XML::Smart save

Question

I realised there is a problem with warn after the use of XML::Smart save.

#!/usr/bin/perl

use strict;
use warnings;

use XML::Smart;

my $XML = XML::Smart->new() ;

print STDOUT "Before save: Print to STDOUT works\n";
print STDERR "Before save: Print to STDERR works\n";
warn "Before save: Warn works\n";

$XML->save('newfile.xml') ;

print STDOUT "After save: Print to STDOUT works\n";
print STDERR "After save: Print to STDERR works\n";
warn "After save: Warn does not work\n";

Test is done in OSX 10.8.2 perl version 5.12.4 xml-smart version 1.77

This is probably closely related to the internal workings of XML::Smart but is there a way to restore printing of warn (reset STDERR).

[EDIT 19/3/2013]: In HP-UX constructor is also problematic. Workaround provided below by ikegami can be used for both new and save to overcome the issue.

Answer 1

As TLP pointed out, the problem is related to XML::Smart's fiddling with $SIG{__WARN__}.

The following is a workaround to the bug:

{
    local $SIG{__WARN__} = $SIG{__WARN__};
    local $SIG{__DIE__}  = $SIG{__DIE__};
    $XML->save('newfile.xml') ;
}

As Borodin explains, this workaround localises the two elements of %SIG that XML::Smart modifies so that the damage is restricted to the enclosing block. The values are automatically restored at the end of the block, immediately after the call to $XML->save.