pass the current key to reduce filter's callback

CHANGELOG

@@ -11,6 +11,7 @@
  * Fix optimizing closures callbacks
  * Add a better exception when getting an undefined constant via `constant`
  * Fix `if` nodes when outside of a block and with an empty body
+ * Arrow functions passed to the "reduce" filter now accept the current key as a third argument
 
 # 3.4.3 (2022-09-28)
 

doc/filters/reduce.rst

@@ -4,21 +4,21 @@
 The ``reduce`` filter iteratively reduces a sequence or a mapping to a single
 value using an arrow function, so as to reduce it to a single value. The arrow
 function receives the return value of the previous iteration and the current
-value of the sequence or mapping:
+value and key of the sequence or mapping:
 
 .. code-block:: twig
 
     {% set numbers = [1, 2, 3] %}
 
-    {{ numbers|reduce((carry, v) => carry + v) }}
-    {# output 6 #}
+    {{ numbers|reduce((carry, v, k) => carry + v * k) }}
+    {# output 8 #}
 
 The ``reduce`` filter takes an ``initial`` value as a second argument:
 
 .. code-block:: twig
 
-    {{ numbers|reduce((carry, v) => carry + v, 10) }}
-    {# output 16 #}
+    {{ numbers|reduce((carry, v, k) => carry + v * k, 10) }}
+    {# output 18 #}
 
 Note that the arrow function has access to the current context.
 

src/Extension/CoreExtension.php

@@ -1703,15 +1703,16 @@ function twig_array_reduce(Environment $env, $array, $arrow, $initial = null)
 {
     twig_check_arrow_in_sandbox($env, $arrow, 'reduce', 'filter');
 
-    if (!\is_array($array)) {
-        if (!$array instanceof \Traversable) {
-            throw new RuntimeError(sprintf('The "reduce" filter only works with arrays or "Traversable", got "%s" as first argument.', \gettype($array)));
-        }
-
-        $array = iterator_to_array($array);
+    if (!\is_array($array) && !$array instanceof \Traversable) {
+        throw new RuntimeError(sprintf('The "reduce" filter only works with arrays or "Traversable", got "%s" as first argument.', \gettype($array)));
     }
 
-    return array_reduce($array, $arrow, $initial);
+    $accumulator = $initial;
+    foreach ($array as $key => $value) {
+        $accumulator = $arrow($accumulator, $value, $key);
+    }
+
+    return $accumulator;
 }
 
 function twig_array_some(Environment $env, $array, $arrow)

tests/Fixtures/filters/reduce_key.test

@@ -0,0 +1,14 @@
+--TEST--
+"reduce" filter passes iterable key to callback
+--TEMPLATE--
+{% set status_classes = {
+    'success': 200,
+    'warning': 400,
+    'error': 500,
+} %}
+
+{{ status_classes|reduce((carry, v, k) => status_code >= v ? k : carry, '') }}
+--DATA--
+return ['status_code' => 404]
+--EXPECT--
+warning