[Serializer] do not transform empty \Traversable to Array

[soyuka]

Q	A
Branch?	4.4
Bug fix?	yes
New feature?	no
Deprecations?	no
Tickets	na
License	MIT
Doc PR	na

Today, using PRESERVE_EMPTY_OBJECTS (introduced in 4.0), the JSON serialization of:

<?php
$object = [];
$object['foo'] = new \ArrayObject();
$object['bar'] = new \ArrayObject(['notempty']);
$object['baz'] = new \ArrayObject(['nested' => new \ArrayObject()]);

Outputs:

{"foo":[],"bar":["notempty"],"baz":{"nested":[]}}

Instead of the expected:

{"foo":{},"bar":["notempty"],"baz":{"nested":{}}}

This issue comes from the Serializer that transforms Traversable to an Array here. Also, the AbstractObjectNormalizer doesn't support Traversable, but he allows to preserve empty objects.

I propose this patch where the fix doesn't transform a Traversable to an Array. I see another way to patch this in which we could allow empty Traversable in the AbstractObjectNormalizer (not sure it's better though). See attached other-fix.patch to see the alternative patch.

[nicolas-grekas]

Thank you @soyuka.

[Gemorroj]

@nicolas-grekas
but why!? it's bc changes. Now empty doctrine collections casts to object instead of empty array

[soyuka]

but why!? it's bc changes. Now empty doctrine collections casts to object instead of empty array

You should not expose ArrayCollection but use ArrayCollection->getValues instead, which will get you a real array (also fixes an index issue if you delete somthing from this ArrayCollection). ArrayCollection is an object and it's correct that it gets normalized to an object imo. Please open an issue if we should discuss this further.

[Plopix]

@Gemorroj issue fixed ;) #37061