Usage of `array_merge_recursive` in `ResolveInfo` can lead to infinite recursion

[Maniload]

Hello 👋

Recently I ran into some weird recursion errors when executing queries like these:

query ExampleQuery {
  user {
    posts {
      id
    }
    ...ExampleFragment
  }
}

fragment ExampleFragment on User {
  posts {
    text
  }
}

This results in a Recursion detected error. It seems like the problem is the way the ResolveInfo class is merging the fields of the query and the fragment. There, the PHP function array_merge_recursive is used:

graphql-php/src/Type/Definition/ResolveInfo.php

Lines 484 to 487 in e165b2e

	$fields = array_merge_recursive(
	$this->foldSelectionWithAlias($fragment->selectionSet, $descend, $fieldType),
	$fields
	);

After some digging I found out, that array_merge_recursive is deeply converting objects to arrays. So in my case it seems like one of my Type implementations is having a reference to itself or is forming a recursive cycle with its references. array_merge_recursive tries to follow this cycle and runs into an infinite loop.

I feel like this deep object conversion is not intended here as it's not documented anywhere in PHP's manual and is not very practical anyways. There's even a bug report from 2005 pointing out this behavior as unintuitive.

While researching I also found this method in QueryPlan:

graphql-php/src/Type/Definition/QueryPlan.php

Lines 280 to 306 in 08f1556

	/**
	* Merges nested arrays, but handles non array values differently from array_merge_recursive.
	* While array_merge_recursive tries to merge non-array values, in this implementation they will be overwritten.
	*
	* @see https://stackoverflow.com/a/25712428
	*
	* @param array<mixed> $array1
	* @param array<mixed> $array2
	*
	* @return array<mixed>
	*/
	private function arrayMergeDeep(array $array1, array $array2): array
	{
	foreach ($array2 as $key => &$value) {
	if (is_numeric($key)) {
	if (! in_array($value, $array1, true)) {
	$array1[] = $value;
	}
	} elseif (is_array($value) && isset($array1[$key]) && is_array($array1[$key])) {
	$array1[$key] = $this->arrayMergeDeep($array1[$key], $value);
	} else {
	$array1[$key] = $value;
	}
	}
	return $array1;
	}

Maybe something like this would also work for ResolveInfo?

Let me know if you need further information or if I can help anywhere.