Add Traversable support of length filter

src/Extension/CoreExtension.php

@@ -1301,22 +1301,18 @@ if (\function_exists('mb_get_info')) {
             return mb_strlen($thing, $env->getCharset());
         }
 
-        if ($thing instanceof \SimpleXMLElement) {
+        if ($thing instanceof \Countable || \is_array($thing) || $thing instanceof \SimpleXMLElement) {
             return \count($thing);
         }
 
-        if (\is_object($thing) && method_exists($thing, '__toString') && !$thing instanceof \Countable) {
-            return mb_strlen((string) $thing, $env->getCharset());
-        }
-
-        if ($thing instanceof \Countable || \is_array($thing)) {
-            return \count($thing);
-        }
-
-        if ($thing instanceof \IteratorAggregate) {
+        if ($thing instanceof \Traversable) {
             return iterator_count($thing);
         }
 
+        if (\is_object($thing) && method_exists($thing, '__toString')) {
+            return mb_strlen((string) $thing, $env->getCharset());
+        }
+
         return 1;
     }
 

test/Twig/Tests/Fixtures/filters/length.test

@@ -11,6 +11,7 @@
 {{ magic|length }}
 {{ non_countable|length }}
 {{ simple_xml_element|length }}
+{{ iterator|length }}
 --DATA--
 return [
     'array' => [1, 4],
@@ -23,6 +24,7 @@ return [
     'magic'         => new MagicCallStub(),     /* used to assert we do *not* call __call */
     'non_countable' => new \StdClass(),
     'simple_xml_element' => new \SimpleXMLElement('<?xml version="1.0" encoding="UTF-8"?><doc><elem/><elem/></doc>'),
+    'iterator' => new \SimpleIteratorForTesting()
 ]
 --EXPECT--
 2
@@ -35,3 +37,4 @@ return [
 1
 1
 2
+7

test/Twig/Tests/IntegrationTest.php

@@ -345,3 +345,40 @@ class IteratorAggregateStub implements \IteratorAggregate
         return new \ArrayIterator($this->data);
     }
 }
+
+class SimpleIteratorForTesting implements Iterator
+{
+    private $data = [1, 2, 3, 4, 5, 6, 7];
+    private $key = 0;
+
+    public function current()
+    {
+        return $this->key;
+    }
+
+    public function next()
+    {
+        ++$this->key;
+    }
+
+    public function key()
+    {
+        return $this->key;
+    }
+
+    public function valid()
+    {
+        return isset($this->data[$this->key]);
+    }
+
+    public function rewind()
+    {
+        $this->key = 0;
+    }
+
+    public function __toString()
+    {
+        // for testing, make sure string length returned is not the same as the `iterator_count`
+        return str_repeat('X', iterator_count($this) + 10);
+    }
+}