my $source = do {
    local(*ARGV, $/);
    @ARGV = $INC{'Util/Stuff.pm'};
    <>;
};

my @packages = $source =~ m/package\s+[_a-zA-Z][^\S;]*;/g;

##</code><code>##

my $mod = Module::Info->new_from_module('Some::Module');
my @packages = $mod->packages_inside;