[PHP-BUG] Bug #71238 [NEW]: usort pass by reference inconsistency

From:             eugen dot alter at gmail dot com
Operating system: any
PHP version:      7.0.1
Package:          Arrays related
Bug Type:         Bug
Bug description:usort pass by reference inconsistency

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) { } } } } } 

-- 
Edit bug report at https://bugs.php.net/bug.php?id=71238&edit=1
-- 
Try a snapshot (PHP 5.4):   https://bugs.php.net/fix.php?id=71238&r=trysnapshot54
Try a snapshot (PHP 5.5):   https://bugs.php.net/fix.php?id=71238&r=trysnapshot55
Try a snapshot (trunk):     https://bugs.php.net/fix.php?id=71238&r=trysnapshottrunk
Fixed in SVN:               https://bugs.php.net/fix.php?id=71238&r=fixed
Fixed in release:           https://bugs.php.net/fix.php?id=71238&r=alreadyfixed
Need backtrace:             https://bugs.php.net/fix.php?id=71238&r=needtrace
Need Reproduce Script:      https://bugs.php.net/fix.php?id=71238&r=needscript
Try newer version:          https://bugs.php.net/fix.php?id=71238&r=oldversion
Not developer issue:        https://bugs.php.net/fix.php?id=71238&r=support
Expected behavior:          https://bugs.php.net/fix.php?id=71238&r=notwrong
Not enough info:            https://bugs.php.net/fix.php?id=71238&r=notenoughinfo
Submitted twice:            https://bugs.php.net/fix.php?id=71238&r=submittedtwice
register_globals:           https://bugs.php.net/fix.php?id=71238&r=globals
PHP 4 support discontinued: https://bugs.php.net/fix.php?id=71238&r=php4
Daylight Savings:           https://bugs.php.net/fix.php?id=71238&r=dst
IIS Stability:              https://bugs.php.net/fix.php?id=71238&r=isapi
Install GNU Sed:            https://bugs.php.net/fix.php?id=71238&r=gnused
Floating point limitations: https://bugs.php.net/fix.php?id=71238&r=float
No Zend Extensions:         https://bugs.php.net/fix.php?id=71238&r=nozend
MySQL Configuration Error:  https://bugs.php.net/fix.php?id=71238&r=mysqlcfg