In moving from Perl 5.22.0 to 5.22.1 I noticed an anomaly using tobyink’s P5U module: p5u v <Module> still finds the module correctly, but in some (not all) cases the version number disappears. Under 5.22.0:

12:24 >p5u v Capture::Tiny
Capture::Tiny
        C:\Perl\Strawberry\strawberry-perl-5.22.0.1-64bit-PDL\perl\ven
+dor\lib\Capture\Tiny.pm: 0.30
[download]

But under 5.22.1:

12:27 >p5u v Capture::Tiny
Capture::Tiny
        C:\Perl\Strawberry\strawberry-perl-5.22.1.1-64bit-PDL\perl\ven
+dor\lib\Capture\Tiny.pm: undef

12:27 >
[download]

Some tortuous debugging¹ eventually led to sub version in Module::Info as the source of the version number. Furthermore, the problem was introduced between version 0.35 (which happens to be the version of Module::Info on my 5.22.0 Perl installation) and version 0.37 (the version on my 5.22.1 installation). But sub version didn’t change between those versions, so what did?

¹Cue The Long and Winding Road.

These lines appear near the head of the code for Module::Info 0.35:

use vars qw($VERSION @ISA $AUTOLOAD);
# quotes 'version' for 5.004
$VERSION = eval 'use version; 1' ? 'version'->new('0.35') : '0.35';
$VERSION = eval $VERSION;
[download]

In 0.37 this has changed to:

our $AUTOLOAD;
our $VERSION;
 
$VERSION = eval 'use version; 1' ? 'version'->new('0.37') : '0.37';
$VERSION = eval $VERSION;
[download]

And, yes, it turns out that the difference in behaviour does result from changing the declaration of $VERSION from use vars to our. Specifically, it’s a problem of scope: use vars (if I understand it correctly) creates a dynamic scope within the current package, whereas our creates a lexical scope that crosses packages within the same file.

Anyway, I came up with a short script that reproduces the problem I’m seeing in Module::Info:

use strict;
use warnings;

package Package_One;

use vars qw( $VERSION );
#our $VERSION;

$VERSION = 'irrelevant';

# "our $VERSION" comes from the target module; without "our" there's n
+o problem

my $eval =<<'END_EVAL';
    no strict;
    local $VERSION;
    $VERSION=undef; do {
      our $VERSION = 'desired_version';
    }; 
    $VERSION
END_EVAL

printf "Version: %s\n", Package_Two->_eval($eval);

package Package_Two;

sub _eval
{
    eval  $_[1];
}
[download]

This script works correctly: it prints Version: desired_version. But when I change the declarations:

#use vars qw( $VERSION );
our $VERSION;
[download]

the version comes back undefined. Note that this problem goes away if the our inside the do block is removed from $eval:

my $eval =<<'END_EVAL';
    no strict;
    local $VERSION;
    $VERSION=undef; do {
      $VERSION = 'desired_version';
    }; 
    $VERSION
END_EVAL
[download]

— which explains why some modules have the version problem and some don’t: the former have their own package variable $VERSION declared with our, the latter do not.

So, my questions:

1. Am I correct in thinking that this is a bug in the newer version of Module::Info?
2. What role does the do block play in this? If I remove it, the problem seems to go away — but I can’t advocate just removing it, as I don’t understand what it’s there for in the first place. :-(
3. I have “fixed” my local copy of Module::Info by changing our $VERSION back to use vars qw( $VERSION ), but should I recommend it as a patch? Or is there a better fix which retains the our declaration?

I’m posting here before submitting a bug report because I would like to first understand exactly what is happening, and why. Any insight or advice will be appreciated — especially an explanation of how the do block interacts with the surrounding code when it’s evaled. A step-by-step description of which $VERSION is which inside sub _eval would be very helpful, too. :-)

Thanks,

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