Sort collections by key when first element of sort operation is string (even if callable) (#40212)

* Sort collections by key when given a string even when key is callable

* Fix style (minor)

* Add test for sorting by callable string

* Fix style (minor)

Author: cheryllium

src/Illuminate/Collections/Collection.php

@@ -1319,7 +1319,7 @@ protected function sortByMany(array $comparisons = [])
 
                 $result = 0;
 
-                if (is_callable($prop)) {
+                if (! is_string($prop) && is_callable($prop)) {
                     $result = $prop($a, $b);
                 } else {
                     $values = [data_get($a, $prop), data_get($b, $prop)];

tests/Support/SupportCollectionTest.php

@@ -1828,6 +1828,17 @@ public function testSortByString($collection)
         $this->assertEquals([['name' => 'dayle'], ['name' => 'taylor']], array_values($data->all()));
     }
 
+    /**
+     * @dataProvider collectionClassProvider
+     */
+    public function testSortByCallableString($collection)
+    {
+        $data = new $collection([['sort' => 2], ['sort' => 1]]);
+        $data = $data->sortBy([['sort', 'asc']]);
+
+        $this->assertEquals([['sort' => 1], ['sort' => 2]], array_values($data->all()));
+    }
+
     /**
      * @dataProvider collectionClassProvider
      */