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Bug #71238 usort pass by reference inconsistency
Submitted: 2015-12-29 16:38 UTC Modified: 2021-07-15 14:04 UTC
Votes:9
Avg. Score:4.1 ± 1.4
Reproduced:6 of 6 (100.0%)
Same Version:4 (66.7%)
Same OS:6 (100.0%)
From: eugen dot alter at gmail dot com Assigned: nikic (profile)
Status: Closed Package: Arrays related
PHP Version: 7.0.1 OS: any
Private report: No CVE-ID: None
 [2015-12-29 16:38 UTC] eugen dot alter at gmail dot com
Description:
------------
In PHP 5.4 ... 5.6 passing compared array elements by reference and then changing them from inside comparison function works properly whilst in PHP7 it does not.

In sample script: function tries to sort arrays by key "name" on all nested levels. The nested levels are sorted correctly on PHP 5.4 .. 5.6 but not on PHP7.

Test script:
---------------
$array = [
    [
        'name'     => 'Foo',
        'children' => [
            [
                'name'     => 'B',
                'children' => []
            ],
            [
                'name'     => 'A',
                'children' => []
            ]
        ]
    ],
    [
        'name'     => 'Bar',
        'children' => [
            [
                'name'     => 'Z',
                'children' => []
            ],
            [
                'name'     => 'X',
                'children' => []
            ],
            [
                'name'     => 'Y',
                'children' => []
            ]
        ]
    ]
];

usort($array, $f = function(&$x, &$y) use (&$f){
    usort($x['children'], $f);
    usort($y['children'], $f);
    return strcasecmp($x['name'], $y['name']);
});

Expected result:
----------------
array(2) { [0]=> array(2) { ["name"]=> string(3) "Bar" ["children"]=> array(3) { [0]=> array(2) { ["name"]=> string(1) "X" ["children"]=> array(0) { } } [1]=> array(2) { ["name"]=> string(1) "Y" ["children"]=> array(0) { } } [2]=> array(2) { ["name"]=> string(1) "Z" ["children"]=> array(0) { } } } } [1]=> array(2) { ["name"]=> string(3) "Foo" ["children"]=> array(2) { [0]=> array(2) { ["name"]=> string(1) "A" ["children"]=> array(0) { } } [1]=> array(2) { ["name"]=> string(1) "B" ["children"]=> array(0) { } } } } }

Actual result:
--------------
array(2) { [0]=> array(2) { ["name"]=> string(3) "Bar" ["children"]=> array(3) { [0]=> array(2) { ["name"]=> string(1) "Z" ["children"]=> array(0) { } } [1]=> array(2) { ["name"]=> string(1) "X" ["children"]=> array(0) { } } [2]=> array(2) { ["name"]=> string(1) "Y" ["children"]=> array(0) { } } } } [1]=> array(2) { ["name"]=> string(3) "Foo" ["children"]=> array(2) { [0]=> array(2) { ["name"]=> string(1) "B" ["children"]=> array(0) { } } [1]=> array(2) { ["name"]=> string(1) "A" ["children"]=> array(0) { } } } } } 

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 [2015-12-29 18:24 UTC] levim@php.net
Using var_export in PHP 5.5:

array (
  0 => 
  array (
    'name' => 'Bar',
    'children' => 
    array (
      0 => 
      array (
        'name' => 'X',
        'children' => 
        array (
        ),
      ),
      1 => 
      array (
        'name' => 'Y',
        'children' => 
        array (
        ),
      ),
      2 => 
      array (
        'name' => 'Z',
        'children' => 
        array (
        ),
      ),
    ),
  ),
  1 => 
  array (
    'name' => 'Foo',
    'children' => 
    array (
      0 => 
      array (
        'name' => 'A',
        'children' => 
        array (
        ),
      ),
      1 => 
      array (
        'name' => 'B',
        'children' => 
        array (
        ),
      ),
    ),
  ),
)

Using var_export in a slightly outdated master branch:

array (
  0 => 
  array (
    'name' => 'Bar',
    'children' => 
    array (
      0 => 
      array (
        'name' => 'Z',
        'children' => 
        array (
        ),
      ),
      1 => 
      array (
        'name' => 'X',
        'children' => 
        array (
        ),
      ),
      2 => 
      array (
        'name' => 'Y',
        'children' => 
        array (
        ),
      ),
    ),
  ),
  1 => 
  array (
    'name' => 'Foo',
    'children' => 
    array (
      0 => 
      array (
        'name' => 'B',
        'children' => 
        array (
        ),
      ),
      1 => 
      array (
        'name' => 'A',
        'children' => 
        array (
        ),
      ),
    ),
  ),
)
 [2016-01-03 14:46 UTC] white06tiger+PHPbug at gmail dot com
I have the same issue with `uksort()` and WITHOUT modifying the actual array.
This bug seems to trigger as soon as anything accesses the array to be sorted.

Following code is supposed to sort an array by values and key (in this case, behaves like a stable sort)

```
<?php
error_reporting(-1);
header('Content-Type: text/plain');

function uasort_key(&$arr, $func) {
	return uksort($arr, function($a,$b) use(&$arr,$func) {
		return $func($arr[$a], $arr[$b], $a, $b);
	});
}

function sort_me($a, $b, $ka = 0, $kb = 0) {
	return ($a < $b ? -1 : ($a > $b ? 1 :
		($ka < $kb ? -1 : ($ka > $kb ? 1 : 0))
	));
}



$test_array = array(4,6,2,1,7,5,1,34,1,0,4);
$test_array_uasort = $test_array;
$test_array_uasort_key = $test_array;

uasort($test_array_uasort, 'sort_me');
uasort_key($test_array_uasort_key, 'sort_me');

echo 'PHP: ', phpversion(), "\n\n";
echo 'Unsorted: ';
print_r($test_array);
echo 'uasort: ';
print_r($test_array_uasort);
echo 'uasort_key: ';
print_r($test_array_uasort_key);

echo "\n\n", 'Source: ', "\n\n";
readfile(__FILE__);
?>
```


In PHP 5.3 you'll get the false-positive warning:
“Warning: uksort(): Array was modified by the user comparison function in sort_bug.php on line 8” which got seemingly fixed in bug #50688 for PHP 7.. Maybe said "fix" introduced our current faulty behavior.

Expected result (PHP 5.3):
-----
uasort_key: Array
(
    [9] => 0
    [3] => 1
    [6] => 1
    [8] => 1
    [2] => 2
    [0] => 4
    [10] => 4
    [5] => 5
    [1] => 6
    [4] => 7
    [7] => 34
)
-----

Actual result (PHP 7.0.1):
-----
uasort_key: Array
(
    [9] => 0
    [6] => 1
    [3] => 1
    [2] => 2
    [0] => 4
    [1] => 6
    [10] => 4
    [8] => 1
    [5] => 5
    [4] => 7
    [7] => 34
)
-----
 [2021-07-15 14:04 UTC] nikic@php.net
-Status: Open +Status: Closed -Assigned To: +Assigned To: nikic
 [2021-07-15 14:04 UTC] nikic@php.net
As of PHP 8.0 this will throw warnings along the lines of:

Warning: {closure}(): Argument #1 ($x) must be passed by reference, value given in /in/UfuCq on line 37

Warning: {closure}(): Argument #2 ($y) must be passed by reference, value given in /in/UfuCq on line 37

Which should make it clear that references are intentionally not supported here, rather than just silently ignoring them.
 
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