Forms API fixes #4: node submission, trees

To reproduce:

create a simple node type, or use an existing on (page, story should work) Add this code to hook_validate so you can see what's going on:

drupal_set_message("In hook_validate, title is $node->title");

Enter a title, "foo".

Hit Preview

What happens behind the scenes is

1) hook_validate is called without taking into account $POST['edit']. That is, title is null.
2) hook_validate is not called with title= foo. More importantly, no values from the form are validated.

The problem starts with this call to node_preview (in node.module):

  if ($op == t('Preview')) {
    $form['node_preview'] = array('#value' => node_preview(array2object($_POST['edit'])), '#weight' => -100);
  }

While node_preview tries to validate the "node" created from $_POST['edit'], it never does, because the node has no type (it can't determine which module to invoke hook_validate).

One fix might be to change:

  $form['type']    = array('#type' => 'value', '#value' => $node->type);

into:

  $form['type']    = array('#type' => 'hidden', '#value' => $node->type);

This would set $_POST['edit']['type'] and cause node_preview to actually call hook_validate. If you try this, you'll see hook_validate is called twice. The first call should not occur, IMHO, but that's another issue I guess.

I suspect some others of these should be hidden fields and not just form values, for the same reason:
(see node.module)

  /**
   * Basic node information.
   * These elements are just values so they are not even sent to the client.
   */
  $form['nid']     = array('#type' => 'value', '#value' => $node->nid);
  $form['vid']     = array('#type' => 'value', '#value' => $node->vid);
  $form['uid']     = array('#type' => 'value', '#value' => $node->uid);
  $form['created'] = array('#type' => 'value', '#value' => $node->created);
  $form['changed'] = array('#type' => 'value', '#value' => $node->changed);
  $form['type']    = array('#type' => 'hidden', '#value' => $node->type);