Public query vars are those available and usable via a direct URL query.

On my site, I\'ve created some custom URLs with their own query variables like so:

example.net/?category_name=uk&tag=highlights

(e.g. list posts that belong to both - the \'Tech\' category and \'gadgets\' tag)

And have rewrite rules (using add_rewrite_rule) in place to pretty the URLs, for example, like this:

example.net/uk/tag/highlights/

(The category base is removed by default from category permalinks.)

Now, the problem with using public query vars is that, they almost never show a 404 error page. For example, take a look these two URLs:

example.net/?category_name=uk&tag=jdfjdsjfdlkf
example.net/uk/tag/jdfjdsjfdlkf

Even though the tag jdfjdsjfdlkf doesn\'t exist, the visitor is shown a "Nothing found" page (content-none.php) instead of throwing a 404 error (404.php) with appropriate headers.

When I think about it, it does make sense. But to suit my specific case, I want a specific set of public query vars (category_name, tag, and channel - a custom taxonomy query_var) to show a 404 error page when the value supplied doesn\'t exist.

My initial attempts got me here:

add_action( \'template_redirect\', \'my_page_template_redirect\' );
function my_page_template_redirect() {

    global $wp_query, $post;

    $cat = get_query_var( \'category_name\' );
    $category = get_term( $cat, \'category\' );

    $chnl = get_query_var( \'channel\' );
    $channel = get_term( $chnl, \'itsme_channel\' );

    $tag = get_query_var( \'tag\' );
    $post_tag = get_term( $tag, \'post_tag\' );

    if( $category && !is_wp_error($category) && $channel && !is_wp_error($channel) ){
    // If URL is like `example.net/?category_name=uk&channel=tech` and both of the
    // supplied values (i.e. Category and Channel taxonomy terms) exist

        // Do nothing

    } elseif( $category && !is_wp_error($category) && $post_tag && !is_wp_error($post_tag) ) {
    // If URL is like `example.net/?category_name=uk&tag=highlights` and both of the
    // supplied values (i.e. Category and Tag taxonomy terms) exist

        // Do nothing

    } elseif( $category && !is_wp_error($category) && $channel && !is_wp_error($channel) && $post_tag && !is_wp_error($post_tag) ) {
    // If URL is like `example.net/?category_name=uk&channel=tech&tag=highlights` and all the
    // supplied values (i.e. Category, Channel, and Tag taxonomy terms) exist

        // Do nothing

    } else {
    // If one or all of the supplied values don\'t exist throw a 404 error

        $wp_query->set_404();
        status_header(404);
        nocache_headers();

    }
}

Problem

Looks like the conditions in place are wrong, or the term objects ($category, $channel, $post_tag aren\'t set properly), as I am always shown a 404 error page, i.e. even if the terms exist.

What am I doing wrong here?