I worked up a test hack that so far appears to work, using a check with MetaCPAN::Client. Essentially it iterates over each file found, and stops checking after it finds one that's a distribution.

I never thought of the Meta files as Anonymonk suggested. I like that idea better as it will save a load of processing time and in some cases many repeated calls to MetaCPAN's API. I'll write out some test code using a meta parser as well and do some testing.

sub revdeps {
    my $self = shift;

    load 'MetaCPAN::Client';
    my $mcpan = MetaCPAN::Client->new;

    my $log = $log->child('revdeps');
    $log->_6('running --revdep');

    my $mod;

    find({
        wanted => sub {
                return if $mod;

                if (-f && $_ =~ /\.pm$/){

                    $log->_6("processing module '$_'");

                    s|lib/||;
                    s|/|-|g;
                    s|\.pm||;

                    $log->_6("module file converted to '$_'");

                    my $dist;

                    eval {
                        $dist = $mcpan->distribution($_);
                    };

                    $mod = $_ if ref $dist;

                }
            },
            no_chdir => 1,
        },
        'lib/'
    );

    $log->_7("using '$mod' as the project we're working on");

    my @revdeps = $self->_get_revdeps($mod);
    return @revdeps;
}
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