When a form element doesn't specify a #weight, it is assumed internally as #weight 0. However, to ensure that our form elements display visually *as they were defined in the array* we, in form_builder, count the number of elements, divide by 1000, and set that as the weight:
# Assign a decimal placeholder weight to preserve original array order
if (!isset($form[$key]['#weight'])) {
$form[$key]['#weight'] = $count/1000;
}
The above code will set the #weights of elements that have not defined a weight to something like 0 (first element in array definition), 0.001, 0.002, and so on. However, anytime a form element *explicitly* defines a #weight of 0, that #weight is kept at exactly 0, which would cause that form element to appear BEFORE the elements that didn't have a #weight defined (and thus received a #weight such as 0.002).
Consider the following pseudo example:
$form['game_title'] = array(
'#type' => 'textfield',
...
);
$form['game_description'] = array(
'#type' => 'textarea',
...
);
$form['game_format'] = filter_form(variable_get('game_format', NULL));
return $form;
Here, we're not definiing weights on our two textfields. We then add an filter_form. The second parameter of the filter_form is $weight, which defaults to 0. After this $form hits form_builder, we have weights 0 (game_title), 0.001 (game_description), and 0 (filter_form) respectively. This is then sorted by weight, which causes filter_form (the third element in the array) to appear BEFORE game_description (0 is lighter than 0.001).
The short lesson is: explicitly defining #weight 0 for a form element is probably a bad idea. This patch changes the default #weight of filter_form to NULL, instead of 0, and also removes any other explicit setting of #weight to 0 in core.
There are a number of small optimizations we could add; like, we should never do more lookup queries than the number of unique URL aliases in the database. When the size of the static cache equals the number of unique URL aliases in the database, we can stop doing lookups. I think this could be implemented with a 2-line change. Takers?
Gerhard Killesreiter
Dries Buytaert
Steven Wittens