[8.x] Pass $key to closure in Collection and LazyCollection's reduce method as well

src/Illuminate/Collections/Collection.php

@@ -872,36 +872,6 @@ public function random($number = null)
         return new static(Arr::random($this->items, $number));
     }
 
-    /**
-     * Reduce the collection to a single value.
-     *
-     * @param  callable  $callback
-     * @param  mixed  $initial
-     * @return mixed
-     */
-    public function reduce(callable $callback, $initial = null)
-    {
-        return array_reduce($this->items, $callback, $initial);
-    }
-
-    /**
-     * Reduce an associative collection to a single value.
-     *
-     * @param  callable  $callback
-     * @param  mixed  $initial
-     * @return mixed
-     */
-    public function reduceWithKeys(callable $callback, $initial = null)
-    {
-        $result = $initial;
-
-        foreach ($this->items as $key => $value) {
-            $result = $callback($result, $value, $key);
-        }
-
-        return $result;
-    }
-
     /**
      * Replace the collection items with the given items.
      *

src/Illuminate/Collections/LazyCollection.php

@@ -827,42 +827,6 @@ public function random($number = null)
         return is_null($number) ? $result : new static($result);
     }
 
-    /**
-     * Reduce the collection to a single value.
-     *
-     * @param  callable  $callback
-     * @param  mixed  $initial
-     * @return mixed
-     */
-    public function reduce(callable $callback, $initial = null)
-    {
-        $result = $initial;
-
-        foreach ($this as $value) {
-            $result = $callback($result, $value);
-        }
-
-        return $result;
-    }
-
-    /**
-     * Reduce an associative collection to a single value.
-     *
-     * @param  callable  $callback
-     * @param  mixed  $initial
-     * @return mixed
-     */
-    public function reduceWithKeys(callable $callback, $initial = null)
-    {
-        $result = $initial;
-
-        foreach ($this as $key => $value) {
-            $result = $callback($result, $value, $key);
-        }
-
-        return $result;
-    }
-
     /**
      * Replace the collection items with the given items.
      *

src/Illuminate/Collections/Traits/EnumeratesValues.php

@@ -716,6 +716,42 @@ public function tap(callable $callback)
         return $this;
     }
 
+    /**
+     * Reduce the collection to a single value.
+     *
+     * @param  callable  $callback
+     * @param  mixed $initial
+     * @return mixed
+     */
+    public function reduce(callable $callback, $initial = null)
+    {
+        $result = $initial;
+
+        foreach ($this as $key => $value) {
+            $result = $callback($result, $value, $key);
+        }
+
+        return $result;
+    }
+
+    /**
+     * Reduce an associative collection to a single value.
+     *
+     * @param  callable  $callback
+     * @param  mixed $initial
+     * @return mixed
+     */
+    public function reduceWithKeys(callable $callback, $initial = null)
+    {
+        $result = $initial;
+
+        foreach ($this as $key => $value) {
+            $result = $callback($result, $value, $key);
+        }
+
+        return $result;
+    }
+
     /**
      * Create a collection of all elements that do not pass a given truth test.
      *

tests/Support/SupportCollectionTest.php

@@ -3590,6 +3590,14 @@ public function testReduce($collection)
         $this->assertEquals(6, $data->reduce(function ($carry, $element) {
             return $carry += $element;
         }));
+
+        $data = new $collection([
+            'foo' => 'bar',
+            'baz' => 'qux',
+        ]);
+        $this->assertEquals('foobarbazqux', $data->reduce(function ($carry, $element, $key) {
+            return $carry .= $key.$element;
+        }));
     }
 
     /**