"Content profile registration broken": debugging rogue form validate overrides

Bad coding in a development partner's custom module was the culprit. It was overriding content_profile_registration's setting of a validation function (and every other module's, too).

Inside the custom module's implementation of hook_form_alter() lives the error:

<?php
  switch ($form_id) {
// ... ignore lots of code
    case 'user_register':
// ... ignore more code
// here's the big ugly error
      $form['#validate'] = array('pduser_username_validate');
      break;
// ... ignore some more code
  }
?>

Note also that the switch on form_id is somewhat deprecated and can be replaced with hook_form_user_register_alter() in this case. See http://api.drupal.org/api/function/hook_form_FORM_ID_alter/6

before:

<?php
  '#validate' =>
  array (
    0 => 'user_register_validate',
    1 => 'content_profile_registration_user_register_validate',
  ),
?>

after-- the altered form #validate:

<?php
array (
  0 => 'customuser_username_validate',
)
?>

This was tracked down by drupal_set_message code mostly outputting for form_alter, but zeroed in on when similar var_export code in content_profile_registration's validate function for the user registration form utterly failed to output anything. After visiting 221B Baker Street, London, we deduced that the function wasn't being called at all:

<?php
function content_profile_registration_user_register_validate($form, &$form_state
) {
// ...code removed
  drupal_set_message('aqui'); //@debug
drupal_set_message('<pre>'.var_export($form_state,TRUE).'</pre>');
print 'anger';
}
?>

The right way

Because we know that user module at least has already added a validation function, we can use the array addition notation to add an additional one.

<?php
      $form['#validate'][] = 'customuser_username_validate';
?>

See Unset certain values in an unkeyed PHP array to unset one validator but keep any others.

Resolution