Allow additional validators to fire on file upload

That didn't occur to me, clever. Thanks! I guess this is by design then.

Actually, I can't seem to make that work. Here is my hook_elements code:

/**
 * Implementation of hook_elements().
 */
function my_module_elements() {
  $elements['filefield_widget']['#process'] = 'my_module_filefield_widget_process';
  return $elements;
}

And here is my process callback code:

/**
 * FAPI #process callback.
 */
function my_module_filefield_widget_process($element) {
  $element['#upload_validators']['my_module_file_validate'] = array();
  return $element;
}

I know the _process() callback is being called because one I put a drupal_set_message() in there, it shows up. When I print_r() the $element variable at the end of my _process() callback, it seems to have worked - the fourth #upload_validators validator is there. However, I don't think this is actually doing anything because a) my validate function is never called, and b) when I print out the form in hook_form_alter(), there are only the default three #upload_validators in the form. Any ideas as to what I'm doing wrong?

Thanks!

Ok, I've done a bit of investigating, and here's what I think is the problem, which is why I believe the patch is necessary:

The validation is done in #value_callback. This is called before #process is called in http://api.drupal.org/api/function/_form_builder_handle_input_element/6. Therefore, there is no way for other modules to alter the #upload_validators FAPI property as far as I see. The other modules you referenced do not attempt to alter the #upload_validators property. Setting back to needs review.