Question

I’d like to attach autocomplete to a particular list of fields in Drupal 7. The fields have FIELD_CARDINALITY_UNLIMITED, so there could be anywhere from 1 to whatever. I’m using the following code:

function mymodule_form_alter(&$form, &$form_state, $form_id) {
    if (array_key_exists('mymodule', $form)) {

        $indices = array_filter(
            array_keys($form['mymodule']['und']), 
            function($item) {
                return is_numeric($item);
            }
        );

        foreach($indices as $index) {
            $form['mymodule']['und'][$index]['value']['#autocomplete_path'] = 'api/node/title';
        }
    }
}

…however, my autocomplete behavior is not being attached. I’ve used the exact same code in a similar situation – the only difference is that I was adding the autocomplete to a field that had a cardinality of 1 rather than unlimited. That doesn’t seem like it should change anything. I’ve verified that the autocomplete is attaching by doing a debug($form['mymodule']) after the assignment statement, and it is definitely there. I have also debugged the exact array path I am trying to get in each iteration of the foreach loop, and it is definitely the correct form value.

EDIT: Is it possible that the issue is with more than one module altering this form using hook_form_alter()? I’m performing the exact same operation as above (but on a single field) in a different module, on the same form.

EDIT2: I’ve noticed that if I put a debug statement inside the foreach loop, I see the autocomplete value is set on the proper value each iteration. If I place the debug statement outside the foreach loop, the autocomplete path is no longer set. Somehow, either during the course of iteration, or after iteration, it looks like my changes are being destroyed? I tested this by assuming $index to be 0, and writing a hard-coded statement to attach autocomplete – this allowed auto complete to work correctly. To be clear, I am seeing something like the following:

function mymodule_form_alter(&$form, &$form_state, $form_id) {
    if (array_key_exists('mymodule', $form)) {

        $indices = array_filter(
            array_keys($form['mymodule']['und']), 
            function($item) {
                return is_numeric($item);
            }
        );

        foreach($indices as $index) {
            $form['mymodule']['und'][$index]['value']['#autocomplete_path'] = 'api/node/title';
            // Debug statements here show that the value '#autocomplete_path' is set properly
            debug($form)['mymodule']['und'][$index]['value']);
        }

        // Now, the '#autocomplete_path' key does not exist
        debug($form)['mymodule']['und'][0]['value']);

        // This will make autocomplete attach correctly
        $form['mymodule']['und'][0]['value']['#autocomplete_path'] = 'api/node/title';
    }
}

Answer 1

I resolved the problem by manually enumerating my indices rather than programmatically doing so, e.g. $form['mymodule']['und'][0]... – this appears to be a PHP issue related to scoping of variables in foreach rather than a Drupal problem.