Allow posts to be filtered before return when `fields` parameter is used with `WP_Query`

[tlovett1]

Right now, when the fields parameter is used with WP_Query ("ids" or "id=>parent"), the returned posts are not filterable at all. Later in WP_Query, the_posts can be used to filter returned posts. This functionality should be mimicked with fields queries.

The use case for this is in plugins that bypass MySQL in WP Query (Elasticsearch). Fields queries right now can not be bypassed.

Patch attached.

[tlovett1]

Add fields_the_posts filters

[adamsilverstein]

This seems super useful, thanks!

When I installed the patch I got this error (twice) when running phpunit:
PHP Fatal error: Call-time pass-by-reference has been removed... (L 3534 & 3534) - looking at the other filters, the ones passing $this by reference all use apply_filters_ref_array

[tlovett1]

Use apply_filters_ref_array

[tlovett1]

Attached another patch. Thanks Adam!

[adamsilverstein]

35476.diff​ :

• Add docblocks for the new hook
• Regenerate from trunk folder

[adamsilverstein]

35476.2.diff​ is a more concise patch: if the filter returns anything but false we return that, otherwise behavior is unchanged. Also, the test_query_fields_integers test now passes.

[welcher]

Adding some unit tests

[hellofromTonya]

The patch adds a new filter which will require a mention in the misc dev note.

[adamsilverstein]

@welcher or @tlovett1 - is this filter still needed? Since we added posts_pre_query in WP4.6, plugins like Elasticpress can filter even fields queries effectively as far as I can tell.

Can you let me know if this is still needed?

• If so, it looks like the code needs to get moved to src/wp-includes/class-wp-query.php now (and I guess tests would move as well).
• If not, let's closed this ticket.