Merge WP_Query args, recursively for meta_query and tax_query

merge-wp-query-args.php

<?php

function merge_wp_query_args(...$sets)
{
	$meta_query = [];
	$tax_query = [];

	foreach ($sets as &$set) {
		if (array_key_exists('meta_query', $set)) {
			$meta_query[] = $set['meta_query'];
			unset($set['meta_query']);
		}

		if (array_key_exists('tax_query', $set)) {
			$tax_query[] = $set['tax_query'];
			unset($set['tax_query']);
		}
	}

	$args = array_merge(...$sets);

	if ($meta_query) {
		$args['meta_query'] = array_merge(...$meta_query);
	}

	if ($tax_query) {
		$args['tax_query'] = array_merge(...$tax_query);
	}

	return $args;
}