[Serializer] XmlEncoder doesn't ignore PI nodes while encoding

[maidmaid]

Q	A
Branch?	master
Bug fix?	no
New feature?	yes
BC breaks?	no
Deprecations?	no
Tests pass?	no
Fixed tickets	/
License	MIT
Doc PR	/

It's sometimes important to get only the XML body without the processing instructions (like the <?xml version="1.0" ?> on the top of your XML doc). At the moment, it's possible to ignore them while decoding, but not while encoding.

$encoder = new XmlEncoder('response', null, $ignoredNodeTypes = [XML_PI_NODE]);
echo $encoder->encode([], 'xml');

Expected:
<response/>

Actual:
<?xml version="1.0"?>
<response/>

So, a new $encoderIgnoredNodeTypes arg is added to the constructor which will be:

public function __construct(string $rootNodeName = 'response', int $loadOptions = null, array $decoderIgnoredNodeTypes = array(XML_PI_NODE, XML_COMMENT_NODE), array $encoderIgnoredNodeTypes = array())

[dunglas]

We follow the robustness principle "Be conservative in what you send, be liberal in what you accept", so while it's ok to ignore XML_PI_NODE by default when decoding, it must be generated by default when encoding.

I suggest to add a new constructor parameter:

public function __construct(string $rootNodeName = 'response', int $loadOptions = null, array $decoderIgnoredNodeTypes = array(XML_PI_NODE, XML_COMMENT_NODE), array $encoderIgnoredNodeTypes = array())

[maidmaid]

I followed your suggestion @dunglas, could you review ?

[nicolas-grekas]

Is the "BC break" label still valid? If not can you please update the PR description? Rebase needed btw.

[maidmaid]

@nicolas-grekas Done :)

[dunglas]

Thank you @maidmaid.

[javiereguiluz]

I've created symfony/symfony-docs#10286 to document this new feature. Please, don't forget to create a doc issue for every new feature.