Refactor context session filtering out of the cassession2 method.

question.php

@@ -117,6 +117,12 @@ class qtype_stack_question extends question_graded_automatically_with_countback
      */
     protected $session;
 
+    /**
+     * Special variables in the question which should be exposed to the inputs and answer tests.
+     * @var cas_evaluatable[]
+     */
+    protected $contextsession;
+
     /**
      * @var stack_ast_container[] STACK specific: the teacher's answers for each input.
      */
@@ -415,7 +421,15 @@ class qtype_stack_question extends question_graded_automatically_with_countback
             $this->runtimeerrors[$s] = true;
         }
 
-        $contextsession = $this->session->get_contextsession();
+        // Set up the context session for this question.
+        $contextsession = array();
+        foreach ($this->session->get_session() as $statement) {
+            if (method_exists($statement, 'is_toplevel_property') && $statement->is_toplevel_property('contextvariable')) {
+                $contextsession[] = $statement;
+            }
+        }
+        $this->contextsession = $contextsession;
+
         foreach ($this->prts as $name => $prt) {
             $prt->add_contextsession($contextsession);
         }
@@ -463,7 +477,6 @@ class qtype_stack_question extends question_graded_automatically_with_countback
      * teacher's model answers.
      */
     protected function adapt_inputs() {
-        $contextsession = $this->session->get_contextsession();
         foreach ($this->inputs as $name => $input) {
             // TODO: again should we give the whole thing to the input.
             $teacheranswer = '';
@@ -471,7 +484,7 @@ class qtype_stack_question extends question_graded_automatically_with_countback
                 $teacheranswer = $this->tas[$name]->get_value();
             }
             $input->adapt_to_model_answer($teacheranswer);
-            $input->add_contextsession($contextsession);
+            $input->add_contextsession($this->contextsession);
         }
     }
 

stack/cas/cassession2.class.php

@@ -328,7 +328,7 @@ class stack_cas_session2 {
             $line .= stack_utils::php_string_to_maxima_string($statement->get_source_context());
             $line .= ')';
 
-            if ($statement->is_toplevel_property('blockexternal')) {
+            if (method_exists($statement, 'is_toplevel_property') && $statement->is_toplevel_property('blockexternal')) {
                 $preblock .= $line . "$\n";
             } else {
                 $command .= self::SEP . $line;
@@ -534,20 +534,6 @@ class stack_cas_session2 {
         return trim($keyvals);
     }
 
-    /*
-     * This is used to extract all the expressions for which "blockexternal" is true.
-     * This enables some context variables to communicate between the castext parts and the inputs.
-     */
-    public function get_contextsession() {
-        $contextsession = array();
-        foreach ($this->statements as $statement) {
-            if ($statement->is_toplevel_property('contextvariable')) {
-                $contextsession[] = $statement;
-            }
-        }
-        return $contextsession;
-    }
-
     public function get_debuginfo() {
         if (trim($this->timeouterrmessage) !== '') {
             return $this->timeouterrmessage;

stack/input/inputbase.class.php

@@ -52,7 +52,7 @@ abstract class stack_input {
     protected $name;
 
     /**
-     * Special variables in the question which should be exposed to the inputs.
+     * Special variables in the question which should be exposed to the inputs and answer tests.
      * @var cas_evaluatable[]
      */
     protected $contextsession = array();