Change active parent menu and child menu items in WordPress Dashboard sidebar

menu.php

<?php
// Below are some example fixes for a structure such as this:
//
// Post Type: lesson (Hidden from menu)
// Taxonomy: course (Hidden from menu)
// Taxonomy: cohort (Hidden from menu)
// And a Gravity Form with ID 3, which links to the Entries page
//
// Note that cm_is_taxonomy_page() and cm_is_homework_entries_page() check the current page using $pagenow, $typenow, and $_GET.
// They are not included

// Fix the Courses and Entries dashboard pages. They do not get highlighted properly.
function cm_student_dashboard_fix_course_menu($parent_file) {
	global $plugin_page;
	
	$post_type_slug = 'edit.php?post_type=lesson';
	$tax_course_slug = 'edit-tags.php?taxonomy=course&post_type=lesson';
	$tax_cohort_slug = 'edit-tags.php?taxonomy=cohort&post_type=lesson';
	
	if ( cm_is_taxonomy_page('course') ) {
		$parent_file = $post_type_slug;
		$plugin_page = $tax_course_slug;
	}
	
	if ( cm_is_taxonomy_page('cohort') ) {
		$parent_file = $post_type_slug;
		$plugin_page = $tax_cohort_slug;
	}
	
	// taxonomy file ($plugin_page) also needed for this page for some reason
	// @see https://stackoverflow.com/a/28856349
	if ( cm_is_homework_entries_page() ) {
		$parent_file = $post_type_slug;
		$plugin_page = $tax_course_slug;
	}
	
	return $parent_file;
}
add_filter('parent_file', 'cm_student_dashboard_fix_course_menu', 30);

// Fix the submenu_file to the actual url that is used for our pages
function cm_student_dashboard_fix_course_submenu($submenu_file) {
	if ( cm_is_taxonomy_page('course') ) {
		$submenu_file = 'edit-tags.php?taxonomy=course&post_type=lesson';
	}
	
	if ( cm_is_taxonomy_page('cohort') ) {
		$submenu_file = 'edit-tags.php?taxonomy=cohort&post_type=lesson';
	}
	
	if ( cm_is_homework_entries_page() ) {
		$submenu_file = 'admin.php?page=gf_entries&id=3';
	}
	
	return $submenu_file;
}
add_filter( 'submenu_file', 'cm_student_dashboard_fix_course_submenu', 30);