_fields parameter doesn't get nested proprieties from custom attribute

[Dudo]

I've added a meta_key with register_meta, with this code

register_meta('post', 'yasr_overall_rating',
        array(
            'show_in_rest' => true,
            'single'       => true,
            'type'         => 'number',
            'auth_callback' => function() {
                return current_user_can('edit_posts');
            }
        )
    );

I can reach the nested proprieties successful with this:

?_fields=meta.yasr_overall_rating

But, I can't access the nested proprieties of a custom attribute, added with this code:

    $visitor_votes_obj = new YasrDatabaseRatings();

    $yasr_vv_schema = array(
        'description'          => 'Yasr Visitor Votes Data',
        'type'                 => 'object',
        'context'              => array('view', 'edit'),
        'properties'           => array(
            'sum_votes' => array(
                'type'  => 'integer',
            ),
            'number_of_votes' => array(
                'type'        => 'integer',
            ),
        ),
    );

register_rest_field(
        'post'
        'yasr-visitor-votes',
        array(
            'get_callback'    => (array($visitor_votes_obj, 'getVisitorVotes')),
            'update_callback' => null,
            'schema'          => $yasr_vv_schema
        )
    );

I can reach successful the attribute yasr-visitor-votes with this:

?_fields=yasr-visitor-votes

But I can't access the nested properties

?_fields=yasr-visitor-votes.sum_votes
?_fields=yasr-visitor-votes.number_of_votes

[kadamwhite]

Nice catch @Dudo, thank you for the ticket.

This happens because we were checking for field names with in_array in the REST Controller when iterating through additional fields, instead of using the more powerful new rest_is_field_included method. Switching to using that method causes the top-level field to be included if any child is present. Once that field is included, then the filtering logic (which runs on a hook within the server) can properly do its job to filter down to leaf nodes.

@TimothyBlynJacobs can you check my work here?

We could pull out the global field resets into a separate commit, those aren't strictly necessary for this patch, it just felt like missing cleanup in the test suite.

[TimothyBlynJacobs]

Switching to rest_is_field_included makes sense to me.

It seems like the global $wp_rest_additional_fields; $wp_rest_additional_fields = array(); pattern should probably be a part of the tearDown for that controller?

[kadamwhite]

Move cleanup to tearDown and resolve PHPCS/Syntax errors

[kadamwhite]

In 47511:

REST API: Fix _fields filtering of registered rest fields.

Use rest_is_field_included when determining which additional fields to include to permit filtering by nested field properties.

Props Dudo, kadamwhite, TimothyBlynJacobs.
Fixes #49648.

[whyisjake]

In 47563:

REST API: Fix _fields filtering of registered rest fields.

Use rest_is_field_included when determining which additional fields to include to permit filtering by nested field properties.

Backportting r47511 to the 5.4 branch.

Props Dudo, kadamwhite, TimothyBlynJacobs.
Fixes #49648.