Auto-linking filters: fix serious caching bug in forum mailouts

Autolinking of glossaries, activity, resources and wiki names were using a
trivial single-entry cache implemented with static vars. The cache was _not_
keyed on course.

This bug was visible during forum_cron() which walks many courses. The cache
would get "stuck" on the first course that had something to put in the cache.
All mailouts from there onwards would autolink to stuff in the wrong course.

filter/activitynames/filter.php

@@ -8,12 +8,20 @@ function activitynames_filter($courseid, $text) {
 
         global $CFG;
 
+        // Trivial-cache - keyed on $cachedcourseid
         static $activitylist;
+        static $cachedcourse;
 
         if (empty($courseid)) {
             $courseid = SITEID;
         }
 
+        // Initialise/invalidate our trivial cache if dealing with a different course
+        if (!isset($cachedcourseid) || $cachedcourseid !== (int)$courseid) {
+            $activitylist = array();
+        } 
+        $cachedcourseid = (int)$courseid;
+
         /// It may be cached
 
         if (empty($activitylist)) {

mod/glossary/filter.php

@@ -3,17 +3,26 @@
 function glossary_filter($courseid, $text) {
     global $CFG;
 
+    // Trivial-cache - keyed on $cachedcourseid
     static $nothingtodo;
     static $conceptlist;
-
-    if (!empty($nothingtodo)) {   // We've been here in this page already
-        return $text;
-    }
+    static $cachedcourseid;
 
     if (empty($courseid)) {
         $courseid = SITEID;
     }
 
+    // Initialise/invalidate our trivial cache if dealing with a different course
+    if (!isset($cachedcourseid) || $cachedcourseid !== (int)$courseid) {
+        $conceptlist = array();
+        $nothingtodo = false;
+    } 
+    $cachedcourseid = (int)$courseid;
+
+    if ($nothingtodo === true) {
+        return $text;
+    }
+
 /// Create a list of all the concepts to search for.  It may be cached already.
 
     if (empty($conceptlist)) {

mod/resource/filter.php

@@ -7,15 +7,24 @@ function resource_filter($courseid, $text) {
 
         global $CFG;
 
+        // Trivial-cache - keyed on $cachedcourseid
         static $nothingtodo;
         static $resourcelist;
+        static $cachedcourseid;
 
-        if (!empty($nothingtodo)) {   // We've been here in this page already
+        // if we don't have a courseid, we can't run the query, so
+        if (empty($courseid)) {
             return $text;
         }
 
-        // if we don't have a courseid, we can't run the query, so
-        if (empty($courseid)) {
+        // Initialise/invalidate our trivial cache if dealing with a different course
+        if (!isset($cachedcourseid) || $cachedcourseid !== (int)$courseid) {
+            $resourcelist = array();
+            $nothingtodo = false;
+        } 
+        $cachedcourseid = (int)$courseid;
+
+        if ($nothingtodo === true) {
             return $text;
         }
 

mod/wiki/filter.php

@@ -10,17 +10,26 @@ function wiki_filter($courseid, $text) {
 
         global $CFG;
 
+        // Trivial-cache - keyed on $cachedcourseid
         static $nothingtodo;
         static $wikipagelist;
-
-        if (!empty($nothingtodo)) {   // We've been here in this page already
-            return $text;
-        }
+        static $cachedcourseid;
 
         if (empty($courseid)) {
             $courseid = SITEID;
         }
 
+        // Initialise/invalidate our trivial cache if dealing with a different course
+        if (!isset($cachedcourseid) || $cachedcourseid !== (int)$courseid) {
+            $wikipagelist = array();
+            $nothingtodo = false;
+        } 
+        $cachedcourseid = (int)$courseid;
+
+        if (!empty($nothingtodo)) {   // We've been here in this page already
+            return $text;
+        }
+
 /// Create a list of all the wikis to search for.  It may be cached already.
 
         if (empty($wikipagelist)) {