Ensure array query parameters do not contain empty items

[roborourke]

Description of the Change

In some cases query args like post__in that are expected to be array might contain invalid data such as an empty string. An array like [ '' ] will not appear as empty when checked with empty( [ '' ] ) so this update ensures the arrays only contain real values. Database IDs all start from 1 so removing 0 is ok here.

This issue was observed with Yoast SEO adding subqueries for indexables to populate post__in parameters, however the index was incomplete. Can also happens in non-production environments where indexables aren't saved to the database.

Alternate Designs

Benefits

Prevents ES query errors such as this one:

Warning[16-Nov-2021 09:00:26 UTC] PHP Warning:  Error in ElasticSearch request: {"error":{"root_cause":[{"type":"query_shard_exception","reason":"failed to create query: empty String","index_uuid":"nRExUs6-TSCUfwX3cBDodg","index":"examplecom-post-2"}],"type":"search_phase_execution_exception","reason":"all shards failed","phase":"query","grouped":true,"failed_shards":[{"shard":4,"index":"examplecom-post-2","node":"-ftiX3JgRtC_yi8bXpnR9A","reason":{"type":"query_shard_exception","reason":"failed to create query: empty String","index_uuid":"nRExUs6-TSCUfwX3cBDodg","index":"examplecom-post-2","caused_by":{"type":"number_format_exception","reason":"empty String"}}}]},"status":400} (400) in /usr/src/app/vendor/altis/cloud/inc/namespace.php on line 365

Note this part:

"caused_by":{"type":"number_format_exception","reason":"empty String"}

Possible Drawbacks

Verification Process

I added this code to as a mu-plugin reproduce the WP Query args as a minimal test case:

add_action( 'pre_get_posts', function( \WP_Query $query ) : void {
	$query->set( 'post__not_in', [ '' ] );
}  );

Observe running a search query yields no results (or falls back to a db query).

The change is intentionally light in terms of sanitisation and I haven observed no regressions with valid values for the listed query arguments, even if provided as strings e.g. (array) "some string" -> [ "some string" ].

Checklist:

• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my change.
• All new and existing tests passed.

Applicable Issues

Changelog Entry

[brandwaffle]

@roborourke thanks for submitting the PR! We'd like to include this in 3.6.5 which will be shipping next week, but that would require fixing the failing tests. Is this something you would have time for in the short term? If not, we can always slot this for a later release. Thanks in advance!

[roborourke]

@brandwaffle I’ll have a crack at the tests tomorrow, some of the failures looked unrelated so I might need a bit of help