#!/usr/bin/perl
use strict; use warnings; use XML::Twig;

my $xml=join('',<DATA>);
my $t=XML::Twig->new(
    start_tag_handlers => {
        _all_ => \&store_line_number,
    },
    twig_handlers => {
        _all_  => \&warn_on_empty_elt,
    },
);
$t->parse($xml);

sub store_line_number {
    my( $twig, $elt)= @_;
    $elt->set_att( '#line' => $twig->current_line);
    $elt->parent->set_att( '#not_empty') if $elt->parent;
}
sub warn_on_empty_elt {
    my( $twig, $elt)= @_;
    if( ! $elt->att( '#not_empty') && $elt->text !~ m{\S}) {
        print $elt->att( '#line'), "\n";
    }
    $twig->purge;
}
__DATA__
<gibsonca>
<abc>fds </abc> <!-- ok -->
<ddd></ddd> <!-- not ok -->
<eee> </eee> <!-- not ok -->
</gibsonca>