MDL-60458 Mathjax: Restore the accessible config

Undo the changes to the accessible config that were introduced by the previous library upgrade.

filter/mathjaxloader/db/upgrade.php

@@ -169,5 +169,33 @@ MathJax.Hub.Config({
         upgrade_plugin_savepoint(true, 2017101200, 'filter', 'mathjaxloader');
     }
 
+    if ($oldversion < 2017102000) {
+        // Re-add Accessible.js (we should not have removed it).
+        $previousdefault = '
+MathJax.Hub.Config({
+    config: ["default.js", "MMLorHTML.js", "Safe.js"],
+    errorSettings: { message: ["!"] },
+    skipStartupTypeset: true,
+    messageStyle: "none"
+});
+';
+        $newdefault = '
+MathJax.Hub.Config({
+    config: ["Accessible.js", "Safe.js"],
+    errorSettings: { message: ["!"] },
+    skipStartupTypeset: true,
+    messageStyle: "none"
+});
+';
+
+        $mathjaxconfig = get_config('filter_mathjaxloader', 'mathjaxconfig');
+
+        if (empty($mathjaxconfig) || filter_mathjaxloader_upgrade_mathjaxconfig_equal($mathjaxconfig, $previousdefault)) {
+            set_config('mathjaxconfig', $newdefault, 'filter_mathjaxloader');
+        }
+
+        upgrade_plugin_savepoint(true, 2017102000, 'filter', 'mathjaxloader');
+    }
+
     return true;
 }

filter/mathjaxloader/readme_moodle.txt

@@ -18,9 +18,3 @@ Upgrading the default MathJax version
 3. Check and eventually update the list of language mappings in filter.php.
    Also see the unit test for the language mappings.
 
-Changes
--------
-
-* The MathJax 2.7.2 seems to have a bug causing the accessibility extensions
-  fail in web apps using RequireJS (such as Moodle). We had to stop using the
-  Accessible.js config for that reason. See MDL-60209 for details.

filter/mathjaxloader/settings.php

@@ -45,7 +45,7 @@ if ($ADMIN->fulltree) {
 
     $default = '
 MathJax.Hub.Config({
-    config: ["default.js", "MMLorHTML.js", "Safe.js"],
+    config: ["Accessible.js", "Safe.js"],
     errorSettings: { message: ["!"] },
     skipStartupTypeset: true,
     messageStyle: "none"

filter/mathjaxloader/version.php

@@ -24,6 +24,6 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-$plugin->version  = 2017101200;
+$plugin->version  = 2017102000;
 $plugin->requires = 2017050500;  // Requires this Moodle version.
 $plugin->component= 'filter_mathjaxloader';