find out if refering to an xs file in a provides field is valid. the metayml spec isn't very clear on that. cpants analyze fails if you do that. the spec also doesn't say if omiting the file field is allowed. cpants reports an error if you do so.

    provides map {
        ("Gtk2::Phat::$_" => { file => "xs/${_}.xs" })
    } (map {
        my $t = $_;
        map { $_ . $t } ('', qw/H V/)
    } qw/FanSlider Keyboard/), 'SliderButton';