MDL-40297 Hide empty categories in my courses

This is a followup of MDL-38631 were was detected that
whith categories being displayed in my courses, some of
them, not having courses for the user, were still shown.

With this patch, any category in the tree, not having courses
is automatically hidden, any depth.

lib/navigationlib.php

@@ -2834,27 +2834,61 @@ protected function load_category($categoryid, $nodetype = self::TYPE_CATEGORY) {
                 $this->add_category($category, $this, $nodetype);
                 $basecategory = $this->addedcategories[$category->id];
             } else {
-                $subcategories[] = $category;
+                $subcategories[$category->id] = $category;
             }
         }
         $categories->close();
 
-        if (!is_null($basecategory)) {
-            foreach ($subcategories as $category) {
-                $this->add_category($category, $basecategory, $nodetype);
-            }
-        }
 
-        // If category is shown in MyHome then only show enrolled courses, else show all courses.
+        // If category is shown in MyHome then only show enrolled courses and hide empty subcategories,
+        // else show all courses.
         if ($nodetype === self::TYPE_MY_CATEGORY) {
             $courses = enrol_get_my_courses();
+            $categoryids = array();
+
+            //only search for categories if basecategory was found
+            if (!is_null($basecategory)) {
+                // get course parent category ids 
+                foreach ($courses as $course) {
+                    $categoryids[] = $course->category;
+                }
+
+                // get a unique list of category ids which a part of the path
+                // to user's courses
+                $course_subcategories = array();
+                $added_subcategories = array();
+
+                list($sql, $params) = $DB->get_in_or_equal($categoryids);
+                $categories = $DB->get_recordset_select('course_categories', 'id '.$sql, $params, 'sortorder, id', 'id, path');
+
+                foreach ($categories as $category){
+                    $course_subcategories = array_merge($course_subcategories, explode('/', trim($category->path, "/")));
+                }
+                $course_subcategories = array_unique($course_subcategories);
+
+                // only add a subcategory if it is part of the path to user's course and
+                // wasn't already added
+                foreach ($subcategories as $sub_id => $subcategory) {
+                    if (in_array($sub_id, $course_subcategories) &&
+                            !in_array($sub_id, $added_subcategories)) {
+                            $this->add_category($subcategory, $basecategory, $nodetype);
+                            $added_subcategories[] = $sub_id;
+                    }
+                }
+            }
+
             foreach ($courses as $course) {
                 // Add course if it's in category.
                 if (in_array($course->category, $categorylist)) {
                     $this->add_course($course, true, self::COURSE_MY);
                 }
             }
         } else {
+            if (!is_null($basecategory)) {
+                foreach ($subcategories as $key=>$category) {
+                    $this->add_category($category, $basecategory, $nodetype);
+                }
+            }
             $courses = $DB->get_recordset('course', array('category' => $categoryid), 'sortorder', '*' , 0, $limit);
             foreach ($courses as $course) {
                 $this->add_course($course);