MDL-48660 Availability: filter_user_list() should respect 'view hidden'

Updated filter_user_list to account for the viewhiddenactivities and
viewhiddensections capabilities.

availability/classes/info.php

@@ -608,12 +608,34 @@ abstract class info {
         }
         $tree = $this->get_availability_tree();
         $checker = new capability_checker($this->get_context());
+
+        // Filter using availability tree.
         $this->modinfo = get_fast_modinfo($this->get_course());
-        $result = $tree->filter_user_list($users, false, $this, $checker);
+        $filtered = $tree->filter_user_list($users, false, $this, $checker);
         $this->modinfo = null;
+
+        // Include users in the result if they're either in the filtered list,
+        // or they have viewhidden. This logic preserves ordering of the
+        // passed users array.
+        $result = array();
+        $canviewhidden = $checker->get_users_by_capability($this->get_view_hidden_capability());
+        foreach ($users as $userid => $data) {
+            if (array_key_exists($userid, $filtered) || array_key_exists($userid, $canviewhidden)) {
+                $result[$userid] = $users[$userid];
+            }
+        }
+
         return $result;
     }
 
+    /**
+     * Gets the capability used to view hidden activities/sections (as
+     * appropriate).
+     *
+     * @return string Name of capability used to view hidden items of this type
+     */
+    protected abstract function get_view_hidden_capability();
+
     /**
      * Formats the $cm->availableinfo string for display. This includes
      * filling in the names of any course-modules that might be mentioned.

availability/classes/info_module.php

@@ -109,6 +109,10 @@ class info_module extends info {
         return parent::filter_user_list($filtered);
     }
 
+    protected function get_view_hidden_capability() {
+        return 'moodle/course:viewhiddenactivities';
+    }
+
     /**
      * Checks if an activity is visible to the given user.
      *

availability/classes/info_section.php

@@ -56,6 +56,10 @@ class info_section extends info {
         return \context_course::instance($this->get_course()->id);
     }
 
+    protected function get_view_hidden_capability() {
+        return 'moodle/course:viewhiddensections';
+    }
+
     protected function set_in_database($availability) {
         global $DB;
         $DB->set_field('course_sections', 'availability', $availability,

availability/classes/tree_node.php

@@ -139,7 +139,8 @@ abstract class tree_node {
 
     /**
      * Tests this condition against a user list. Users who do not meet the
-     * condition will be removed from the list.
+     * condition will be removed from the list, unless they have the ability
+     * to view hidden activities/sections.
      *
      * This function must be implemented if is_applied_to_user_lists returns
      * true. Otherwise it will not be called.
@@ -150,6 +151,10 @@ abstract class tree_node {
      * Within this function, if you need to check capabilities, please use
      * the provided checker which caches results where possible.
      *
+     * Conditions do not need to check the viewhiddenactivities or
+     * viewhiddensections capabilities. These are handled by
+     * core_availability\info::filter_user_list.
+     *
      * @param array $users Array of userid => object
      * @param bool $not True if this condition is applying in negative mode
      * @param \core_availability\info $info Item we're checking