Question

In drupal, an uncatchable php error is thrown by this code:

/*
* @param $variables
*   An associative array containing:
*   - element: An associative array containing the properties of the element.
*     Properties used: #title, #title_display, #description, #id, #required,
*     #children, #type, #name.
*
* @ingroup themeable
*/
function theme_form_element($variables) {
  //print_r($variables); die("daa`");
  $element = &$variables['element'];
  // This is also used in the installer, pre-database setup.
  $t = get_t();

  // This function is invoked as theme wrapper, but the rendered form element
  // may not necessarily have been processed by form_builder().

  $element += array(
    '#title_display' => 'before',
  );
...

The last line of drupal’s function throws the error.

$variables['element'] is an array when it enters the function. When the $element reference is assigned to it, it changes (within $variables) from type Array to type &Array. The variable $element reports itself as type Array.

The following lines no not throw the same error when used instead of the += operator:

$element = $element + array();
$new = array_merge($element, array());  

@iputonmyrobeandwizardhat asked for an sscce, which I attempted to provide below. However, the code does not cause the same error in isolation that it throws while in use in drupal’s rendering process. Can anyone recommend a method to isolate the error?

<?php
function theme_form_element($variables) { 
  $element = &$variables['element'];         
  var_dump($variables);                //['element'] becomes type &array

  //not fatal
  $element2 = $element + array( '#title' => 'before'); 

  //not fatal
  $element3 = array_merge($element, array( '#title' => 'before'));   

  $element += array( '#title_display' => 'before');  
    var_dump($element);
}

$variables_array = array
(
'element' => array
    (
        '#type' => 'textfield',
        '#title' => 'First Name:',
        '#default_value' => '',
        '#size' => 60,
        '#maxlength' => 64,
        '#description' => 'First name',
        '#required' => 1,
        '#input' => 1,
        '#autocomplete_path' => '',
        '#process' => Array ('ajax_process_form'),

        '#theme' => 'textfield',
        '#theme_wrappers' => Array('form_element'),

        '#defaults_loaded' => 1,
        '#tree' => '',
        '#parents' => Array('first_name'),

        '#array_parents' => Array('first_name'),

        '#weight' => 0,
        '#processed' => 1,
        '#attributes' => Array(),

        '#title_display' => 'before',
        '#id' => 'edit-first-name',
        '#name' => 'first_name',
        '#value' => '',
        '#ajax_processed' => '',
        '#sorted' => 1,
        '#children' => '<input type="text" id="edit-first-name" name="first_name" value="" size="60" maxlength="64" class="form-text required" />'
    )

);    
?>

The input:

// base64_encode(serialize($variables));
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

Answer 1

+= works fine with arrays and references.

$arr = array(1);
$e = &$arr;
$e += array(1,2);

print_r($e);//Array ( [0] => 1 [1] => 2 )

http://codepad.org/0M5ChPgt