这不是怎么回事pre_get_posts 作品

pre\\u get\\u posts操作允许开发人员通过引用访问$query对象(any changes you make to $query are made directly to the original object - no return value is necessary).

https://codex.wordpress.org/Plugin_API/Action_Reference/pre_get_posts

你所做的完全是错误的。您不会通过“返回”另一个查询pre_get_posts, 您可以更改现有查询。我不知道什么是如此复杂，您无法通过一组适当的过滤器来完成，但如果您必须有一些自定义SQL，那么：

function project_modify_default_search( $query ) {
  if( $query->is_search && $query->is_main_query() && ! isset( $_REQUEST[\'search\'] ) ) {

    //I\'m in my search.php - confirmed

    //Reset default $query - not to execute at all

    //Do my custom complex query and pass the query as a $wp_query object
    //so that I can use the default search.php template
    global $wpdb;
    $searchQ = sanitize_text_field( get_query_var( \'s\' ) );

    // Sample "complex" query
    $complex_query = "SELECT SQL_CALC_FOUND_ROWS {$wpdb->posts}.ID FROM {$wpdb->posts} WHERE {$wpdb->posts}.post_title LIKE \'$searchQ%\' LIMIT 10";

    // Use `get_col` to return a simple array of IDs
    $custom_search_query = $wpdb->get_col( $complex_query );

    // Pass those IDs to the main query
    $query->set(\'post__in\',$custom_search_query);

    // can\'t kill the default search here or it can break some functions.
    // $query->set(\'s\',NULL);

    // So we do this:
    add_action( \'posts_search\', \'__return_empty_string\' );

  } //endif
}
add_action( \'pre_get_posts\', \'project_modify_default_search\' );

同样，可以肯定的是，这是生成复杂查询的错误方法，尤其是考虑到相对于通过一组过滤器修改主查询，您至少有一个额外的查询--posts_where, posts_join, 等