Hotfix Stable solrting

[bpolaszek]

Fixes #663
Related to #657

[goetas]

Can you please explain the reason of this change?

[bpolaszek]

@goetas Sorry, this is related to #663 - this PR fixes a different behavior between PHP versions, handlers wrongly sorted on PHP7+ and correctly sorted in PHP5.

[goetas]

Can you please add some test (by having a big array of listeners)?

[bpolaszek]

@goetas Not sure it's worth the work, since we're dealing with a PHP internal.

JMS\SerializerBundle\Tests\DependencyInjection\CustomHandlerPassTest::testSubscribingHandlerMustRespectPriorities() is already written for that, and keep in mind that with uasort, the result may, or may not, be what is expected.

Try out the following snippet (borrowed from CustomHandlersPass's internal code):

// A closure which will always return 0 because all items will have the same 'fixed_value'.
$sorter = function ($a, $b) {
    return $b['fixed_value'] == $a['fixed_value'] ? 0 : ($b['fixed_value'] > $a['fixed_value'] ? 1 : -1);
};

// Copied from CustomHandlersPass
function stable_uasort(array &$array, $value_compare_func)
{
    $index = 0;
    foreach ($array as &$item) {
        $item = [$index++, $item];
    }
    $result = uasort($array, function ($a, $b) use ($value_compare_func) {
        $result = call_user_func($value_compare_func, $a[1], $b[1]);
        return $result == 0 ? $a[0] - $b[0] : $result;
    });
    foreach ($array as &$item) {
        $item = $item[1];
    }
    return $result;
}


// Now, create an array with a fixed value and a random one.
$a = [];
for ($i = 0; $i < 1000; $i++) {
    $a[] = [
        'fixed_value'  => 'foo',
        'random_value' => mt_rand(0, 10000),
    ];
}


$c = $b = $a; // We now have 3 strictly equal arrays
var_dump($b === $a); // true
var_dump($c === $a); // true

// Use PHP built-in sorting function
uasort($b, $sorter); // $b is sorted, but $b is no longer equal to $a
var_dump($b === $a);// false


stable_uasort($c, $sorter); // $c is sorted, and $c is still strictly equal to $a
var_dump($c === $a);// true

Tested on PHP 7.2 and PHP 5.6. This confirms what CMB said: Stable sorting is not guaranteed with PHP sort functions, even since PHP7+.

I could write a test with 1000 subscribing handlers, sort them and still have them correctly sorted, the point is that PHP's uasort() is clearly unreliable, and in some cases like mine, it will fail.

The existing stable_uasort method is already working and tested with travis on PHP 5+. I have added no code, I just removed the PHP7+ exception.

If you want to be sure that all items are correctly sorted, only the stable_uasort function must be unit tested (then it could be subscribing handlers, foo/bars or fruits), but it's currently protected.

I hope you'll understand my point.

Thank you,
Ben

[goetas]

alright!