MDL-31789: Allowing context object to be passed to JS using json_encode()

Classes with magic properties such as context do not pass through json_encode().
The solution is to implement iterator in such classes and convert what we
feed to json_encode to array using 'foreach' before we pass it to json_encode():
- class context implements IteratorAggregate
- added function convert_to_array() that converts anything to array
- before calling json_encode we convert the argument to array

lib/accesslib.php

@@ -4487,7 +4487,7 @@ function role_change_permission($roleid, $context, $capname, $permission) {
  * @property-read string $path path to context, starts with system context
  * @property-read dept $depth
  */
-abstract class context extends stdClass {
+abstract class context extends stdClass implements IteratorAggregate {
 
     /*
      * Google confirms that no other important framework is using "context" class,
@@ -4695,6 +4695,25 @@ abstract class context extends stdClass {
         debugging('Can not unset context instance properties!');
     }
 
+    // ====== implementing method from interface IteratorAggregate ======
+
+    /**
+     * Create an iterator because magic vars can't be seen by 'foreach'.
+     *
+     * Now we can convert context object to array using convert_to_array(),
+     * and feed it properly to json_encode().
+     */
+    public function getIterator() {
+        $ret = array(
+            'id'           => $this->id,
+            'contextlevel' => $this->contextlevel,
+            'instanceid'   => $this->instanceid,
+            'path'         => $this->path,
+            'depth'        => $this->depth
+        );
+        return new ArrayIterator($ret);
+    }
+
     // ====== general context methods ======
 
     /**

lib/moodlelib.php

@@ -10071,6 +10071,40 @@ function object_property_exists( $obj, $property ) {
     return array_key_exists( $property, $properties );
 }
 
+/**
+ * Converts an object into an associative array
+ *
+ * This function converts an object into an associative array by iterating
+ * over its public properties. Because this function uses the foreach
+ * construct, Iterators are respected. It works recursively on arrays of objects.
+ * Arrays and simple values are returned as is.
+ *
+ * If class has magic properties, it can implement IteratorAggregate
+ * and return all available properties in getIterator()
+ *
+ * @param mixed $var
+ * @return array
+ */
+function convert_to_array($var) {
+    $result = array();
+    $references = array();
+
+    // loop over elements/properties
+    foreach ($var as $key => $value) {
+        // recursively convert objects
+        if (is_object($value) || is_array($value)) {
+            // but prevent cycles
+            if (!in_array($value, $references)) {
+                $result[$key] = convert_to_array($value);
+                $references[] = $value;
+            }
+        } else {
+            // simple values are untouched
+            $result[$key] = $value;
+        }
+    }
+    return $result;
+}
 
 /**
  * Detect a custom script replacement in the data directory that will

lib/outputcomponents.php

@@ -1589,7 +1589,7 @@ class js_writer {
      */
     public static function function_call($function, array $arguments = null, $delay=0) {
         if ($arguments) {
-            $arguments = array_map('json_encode', $arguments);
+            $arguments = array_map('json_encode', convert_to_array($arguments));
             $arguments = implode(', ', $arguments);
         } else {
             $arguments = '';
@@ -1611,7 +1611,7 @@ class js_writer {
      */
     public static function function_call_with_Y($function, array $extraarguments = null) {
         if ($extraarguments) {
-            $extraarguments = array_map('json_encode', $extraarguments);
+            $extraarguments = array_map('json_encode', convert_to_array($extraarguments));
             $arguments = 'Y, ' . implode(', ', $extraarguments);
         } else {
             $arguments = 'Y';
@@ -1630,7 +1630,7 @@ class js_writer {
      */
     public static function object_init($var, $class, array $arguments = null, array $requirements = null, $delay=0) {
         if (is_array($arguments)) {
-            $arguments = array_map('json_encode', $arguments);
+            $arguments = array_map('json_encode', convert_to_array($arguments));
             $arguments = implode(', ', $arguments);
         }
 

lib/outputrequirementslib.php

@@ -715,7 +715,7 @@ class page_requirements_manager {
             // Set Y's config.gallery to the version
             $jscode = 'Y.config.gallery='.json_encode($galleryversion).';';
         }
-        $jscode .= 'Y.use('.join(',', array_map('json_encode', $modules)).',function() {'.js_writer::function_call($function, $arguments).'});';
+        $jscode .= 'Y.use('.join(',', array_map('json_encode', convert_to_array($modules))).',function() {'.js_writer::function_call($function, $arguments).'});';
         if ($ondomready) {
             $jscode = "Y.on('domready', function() { $jscode });";
         }