MDL-38555 forms: Prevent same data submission multiple times.

This disables Submit button when the form has been submitted to
prevent consequent submissions before the page has been loaded.

lib/form/submit.js

@@ -0,0 +1,9 @@
+M.form_submit = {};
+
+M.form_submit.init = function(Y, options) {
+    Y.on('submit', function(e) {
+        if (!containsErrors) {
+            e.target.one('#'+options.submitid).setAttribute('disabled', 'true');
+        }
+    }, '#'+options.formid);
+};

lib/form/submit.php

@@ -38,6 +38,9 @@
  * @license   http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class MoodleQuickForm_submit extends HTML_QuickForm_submit {
+    /** @var string Need to store id of form for submission control in JS*/
+    var $_formid = '';
+
     /**
      * constructor
      *
@@ -60,6 +63,7 @@ function onQuickFormEvent($event, $arg, &$caller)
     {
         switch ($event) {
             case 'createElement':
+                $this->_formid = $caller->getAttribute('id');
                 parent::onQuickFormEvent($event, $arg, $caller);
                 if ($caller->isNoSubmitButton($arg[0])){
                     //need this to bypass client validation
@@ -98,4 +102,22 @@ function freeze(){
         $this->_flagFrozen = true;
     }
 
+    /**
+     * Returns HTML for this form element.
+     *
+     * @return string
+     */
+    function toHtml(){
+        global $PAGE;
+        $options = array(
+            'submitid' => $this->getAttribute('id'),
+            'formid' => $this->_formid,
+        );
+        $str = parent::toHtml();
+        if ($this->getAttribute('onclick') === null) {
+            $module = array('name'=>'form_submit', 'fullpath'=>'/lib/form/submit.js');
+            $PAGE->requires->js_init_call('M.form_submit.init', array($options), true, $module);
+        }
+        return $str;
+    }
 }

lib/formslib.php

@@ -2096,6 +2096,7 @@ function getValidationScript()
 //<![CDATA[
 
 var skipClientValidation = false;
+var containsErrors = false;
 
 function qf_errorHandler(element, _qfMsg) {
   div = element.parentNode;
@@ -2204,6 +2205,7 @@ function validate_' . $this->_formName . '(frm) {
   var frm = document.getElementById(\''. $this->_attributes['id'] .'\')
   var first_focus = false;
 ' . $validateJS . ';
+  containsErrors = !ret;
   return ret;
 }
 //]]>