Fix: prevent "Cannot traverse an already closed generator" error by materializing Traversable input

Author: santysisi

src/Symfony/Component/Serializer/Encoder/CsvEncoder.php

@@ -65,6 +65,10 @@ public function encode(mixed $data, string $format, array $context = []): string
         } elseif (empty($data)) {
             $data = [[]];
         } else {
+            if ($data instanceof \Traversable) {
+                // Generators can only be iterated once — convert to array to allow multiple traversals
+                $data = iterator_to_array($data);
+            }
             // Sequential arrays of arrays are considered as collections
             $i = 0;
             foreach ($data as $key => $value) {

src/Symfony/Component/Serializer/Tests/Encoder/CsvEncoderTest.php

@@ -710,4 +710,28 @@ public function testEndOfLinePassedInConstructor()
         $encoder = new CsvEncoder([CsvEncoder::END_OF_LINE => "\r\n"]);
         $this->assertSame("foo,bar\r\nhello,test\r\n", $encoder->encode($value, 'csv'));
     }
+
+    /** @dataProvider provideIterable */
+    public function testIterable(mixed $data)
+    {
+        $this->assertEquals(<<<'CSV'
+            foo,bar
+            hello,"hey ho"
+            hi,"let's go"
+
+            CSV, $this->encoder->encode($data, 'csv'));
+    }
+
+    public static function provideIterable()
+    {
+        $data = [
+            ['foo' => 'hello', 'bar' => 'hey ho'],
+            ['foo' => 'hi', 'bar' => 'let\'s go'],
+        ];
+
+        yield 'array' => [$data];
+        yield 'array iterator' => [new \ArrayIterator($data)];
+        yield 'iterator aggregate' => [new \IteratorIterator(new \ArrayIterator($data))];
+        yield 'generator' => [(fn (): \Generator => yield from $data)()];
+    }
 }