use Perl

We noticed a lot of "subroutine redefined" warnings in our apache logs. A little investigation later, and it turns out the problem is with recursive uses.

Consider the following modules (named after the classic Italian metasyntactic characters)

package Pippo;
use strict; use warnings;
use Data::Dumper;
BEGIN { warn Dumper( { Pippo => \%INC } ); }
use Pluto;
sub dummy1 { ; }
1;

and

package Pluto;
use strict; use warnings;
use Data::Dumper;
BEGIN { warn Dumper( { Pluto => \%INC } ); }
use Pippo;
sub dummy2 {;}
1;

Here's some output for perl -c (trimming the Dumper output to just show these 2 modules)

$ perl -c Pippo.pm
$VAR1 = {
          'Pippo' => { }
        };
$VAR1 = {
          'Pluto' => {
                       'Pluto.pm' => 'Pluto.pm',
                     }
        };
$VAR1 = {
          'Pippo' => {
                       'Pippo.pm' => 'Pippo.pm',
                       'Pluto.pm' => 'Pluto.pm',
                     }
        };
Subroutine dummy1 redefined at Pippo.pm line 8.
Pippo.pm syntax OK

That is, the first module, Pippo, doesn't set its entry in %INC until after it's finished processing. The use'd module sets its entry in %INC immediately, which is handy, as otherwise we'd have an infinite recursive use. As it is, only Pippo gets used twice, triggering the "Subroutine redefined" warning.

I whined about this in #london.pm, and Nicholas suggested that the timing of this behaviour might possibly be considered a bug. Is there a case for saying that %INC should be set for the file first invoked by perl?

Recursive uses are very likely on the "well don't do that" list, but the timing surprises me in any case.