MDL-40571 work around block editing hacks on admin page

admin/index.php

@@ -47,10 +47,11 @@
 
 define('NO_OUTPUT_BUFFERING', true);
 
-if (empty($_GET['cache']) and empty($_POST['cache'])) {
+if (empty($_GET['cache']) and empty($_POST['cache']) and empty($_GET['sesskey']) and empty($_POST['sesskey'])) {
     // Prevent caching at all cost when visiting this page directly,
     // we redirect to self once we known no upgrades are necessary.
     // Note: $_GET and $_POST are used here intentionally because our param cleaning is not loaded yet.
+    // Note2: the sesskey is present in all block editing hacks, we can not redirect there, so enable caching.
     define('CACHE_DISABLE_ALL', true);
 
     // Force OPcache reset if used, we do not want any stale caches
@@ -449,7 +450,7 @@
 
 // Now we can be sure everything was upgraded and caches work fine,
 // redirect if necessary to make sure caching is enabled.
-if (!$cache) {
+if (!$cache and !optional_param('sesskey', '', PARAM_RAW)) {
     redirect(new moodle_url($PAGE->url, array('cache' => 1)));
 }
 

lib/adminlib.php

@@ -6343,10 +6343,10 @@ function admin_externalpage_setup($section, $extrabutton = '', array $extraurlpa
     if ($PAGE->user_allowed_editing()) {
         if ($PAGE->user_is_editing()) {
             $caption = get_string('blockseditoff');
-            $url = new moodle_url($PAGE->url, array('adminedit'=>'0'));
+            $url = new moodle_url($PAGE->url, array('adminedit'=>'0', 'sesskey'=>sesskey()));
         } else {
             $caption = get_string('blocksediton');
-            $url = new moodle_url($PAGE->url, array('adminedit'=>'1'));
+            $url = new moodle_url($PAGE->url, array('adminedit'=>'1', 'sesskey'=>sesskey()));
         }
         $PAGE->set_button($OUTPUT->single_button($url, $caption, 'get'));
     }