Wordpress custom post type hierarchy and menu highlighting (current_page_parent)

WP ticket: http://core.trac.wordpress.org/ticket/16382

function fix_blog_menu_css_class( $classes, $item ) {
    if ( is_tax( 'my-cat-tax' ) || is_singular( 'my-post-type' ) || is_post_type_archive( 'my-post-type' ) ) {
        if ( $item->object_id == get_option('page_for_posts') ) {
            $key = array_search( 'current_page_parent', $classes );
            if ( false !== $key )
                unset( $classes[ $key ] );
        }
    }

    return $classes;
}
add_filter( 'nav_menu_css_class', 'fix_blog_menu_css_class', 10, 2 );

It appears this is an issue with the core Wordpress code; the code that generates the menu classes adds current_page_parent to your Blog page everywhere except when viewing static page templates.

(This has been discussed in passing at http://core.trac.wordpress.org/ticket/13543).

You can however get around this with some custom code using the page_css_class filter. For example, add something along these lines to functions.php (not 100% tested):

function my_page_css_class($css_class, $page) {
    if (get_post_type()=='portfolio' || is_page(57)) {
        if ($page->ID == get_option('page_for_posts')) {
            foreach ($css_class as $k=>$v) {
                if ($v=='current_page_parent') unset($css_class[$k]);
            }
        }
        if ($page->ID==57) {
            $css_class[]='current_page_parent';
        }
    }
    return $css_class;
}
add_filter('page_css_class','my_page_css_class',10,2);

Replacing 57 with the ID of your portfolios page, of course. That removes current_page_parent when printing the blog page and adds current_page_parent to your portfolios page, when either viewing a single portfolio or viewing the portfolios page itself.

Here is my optimized/extended version of previously suggested solutions, which is pretty much fully automated. No more extra CSS or menu attributes needed.

This version dynamically gets a list of custom post types and if the current post type is a custom post type, then it removes the 'current_page_parent' class from all menu items.

Furthermore it checks each menu item to see if it's for a page with a page template like "page-{custom_post_type_slug}.php", and if so, it'll add the 'current_page_parent' class.

The filter priority is 1, as some themes, replace the current_page_parent/etc. classes with a class like 'active' (eg. 'roots' does this), so this filter needs to execute first.

Lastly, it makes use of 3 static variables since this function is repeatedly called and these (obviously) remain the same through all calls.

function theme_current_type_nav_class($css_class, $item) {
    static $custom_post_types, $post_type, $filter_func;

    if (empty($custom_post_types))
        $custom_post_types = get_post_types(array('_builtin' => false));

    if (empty($post_type))
        $post_type = get_post_type();

    if ('page' == $item->object && in_array($post_type, $custom_post_types)) {
        $css_class = array_filter($css_class, function($el) {
            return $el !== "current_page_parent";
        });

        $template = get_page_template_slug($item->object_id);
        if (!empty($template) && preg_match("/^page(-[^-]+)*-$post_type/", $template) === 1)
            array_push($css_class, 'current_page_parent');

    }

    return $css_class;
}
add_filter('nav_menu_css_class', 'theme_current_type_nav_class', 1, 2);

PS. Just to point out one shortcoming in all non-CSS solutions I've seen so far, including my own: Something not taken into account is highlighting the menu item parent/ancestor of an item linking to a page which displays posts of the current custom post type. Consider a custom post type "product" and a menu like:

Home  Company  News  Contact
      |
      \--About Us
      \--Products

"Products" is a page with a template "page-product.php" and shows an overview of posts of type 'product'. It is highlighted due to posted solution. However 'Company' as its parent/ancestor should also be highlighted, but isn't. Something to keep in mind.