Class::ISA might be useful in this case -- you can just ask each class if it supports 'validate()' and if so print that out, like this untested:

sub validate
{
  my $self = shift;
  # do validation
  foreach my $parent_class ( Class::ISA::super_path( ref $self ) ) {
    if ( $parent_class->can( 'validate' ) ) {
        print "Will call '$parent_class->validate()'\n";
        last;
    }
  }

  return $self->SUPER::validate(@_);
}
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