Keep original keys when using Collection->sortBy() with an array of s…

…ort operations (#43609)

* Add test

* Use usaort instead of usort to keep the original keys

src/Illuminate/Collections/Collection.php

@@ -1366,7 +1366,7 @@ protected function sortByMany(array $comparisons = [])
     {
         $items = $this->items;
 
-        usort($items, function ($a, $b) use ($comparisons) {
+        uasort($items, function ($a, $b) use ($comparisons) {
             foreach ($comparisons as $comparison) {
                 $comparison = Arr::wrap($comparison);
 

tests/Support/SupportCollectionTest.php

@@ -1982,6 +1982,16 @@ public function testSortByAlwaysReturnsAssoc($collection)
         });
 
         $this->assertEquals([1 => 'dayle', 0 => 'taylor'], $data->all());
+
+        $data = new $collection(['a' => ['sort' => 2], 'b' => ['sort' => 1]]);
+        $data = $data->sortBy([['sort', 'asc']]);
+
+        $this->assertEquals(['b' => ['sort' => 1], 'a' => ['sort' => 2]], $data->all());
+
+        $data = new $collection([['sort' => 2], ['sort' => 1]]);
+        $data = $data->sortBy([['sort', 'asc']]);
+
+        $this->assertEquals([1 => ['sort' => 1], 0 => ['sort' => 2]], $data->all());
     }
 
     /**