MDL-46148 qtype_calculated: function to validate equations in text.

Author: timhunt

question/type/calculated/question.php

@@ -278,6 +278,7 @@ public function datasets_are_synchronised($category) {
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class qtype_calculated_variable_substituter {
+
     /** @var array variable name => value */
     protected $values;
 
@@ -466,7 +467,7 @@ protected function substitute_values_pretty($text) {
      */
     public function replace_expressions_in_text($text, $length = null, $format = null) {
         $vs = $this; // Can't use $this in a PHP closure.
-        $text = preg_replace_callback('~\{=([^{}]*(?:\{[^{}]+}[^{}]*)*)}~',
+        $text = preg_replace_callback(qtype_calculated::FORMULAS_IN_TEXT_REGEX,
                 function ($matches) use ($vs, $format, $length) {
                     return $vs->format_float($vs->calculate($matches[1]), $length, $format);
                 }, $text);

question/type/calculated/questiontype.php

@@ -37,6 +37,9 @@
  * @license    http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
  */
 class qtype_calculated extends question_type {
+    /** Regular expression that finds the formulas in content. */
+    const FORMULAS_IN_TEXT_REGEX = '~\{=([^{}]*(?:\{[^{}]+}[^{}]*)*)\}~';
+
     const MAX_DATASET_ITEMS = 100;
 
     public $wizardpagesnumber = 3;
@@ -1984,3 +1987,26 @@ function qtype_calculated_find_formula_errors($formula) {
         return false;
     }
 }
+
+/**
+ * Validate all the forumulas in a bit of text.
+ * @param string $text the text in which to validate the formulas.
+ * @return string|boolean false if there are no problems. Otherwise a string error message.
+ */
+function qtype_calculated_find_formula_errors_in_text($text) {
+    preg_match_all(qtype_calculated::FORMULAS_IN_TEXT_REGEX, $text, $matches);
+
+    $errors = array();
+    foreach ($matches[1] as $match) {
+        $error = qtype_calculated_find_formula_errors($match);
+        if ($error) {
+            $errors[] = $error;
+        }
+    }
+
+    if ($errors) {
+        return implode(' ', $errors);
+    }
+
+    return false;
+}

question/type/calculated/tests/formula_validation_test.php

@@ -83,4 +83,23 @@ public function test_functions_with_wrong_num_args_caught() {
         $this->assert_nonempty_string(qtype_calculated_find_formula_errors('atan2(1.0, 1.0, 2.0)'));
         $this->assert_nonempty_string(qtype_calculated_find_formula_errors('max(1.0)'));
     }
+
+    public function test_validation_of_formulas_in_text_ok() {
+        $this->assertFalse(qtype_calculated_find_formula_errors_in_text(
+                '<p>Look no equations.</p>'));
+        $this->assertFalse(qtype_calculated_find_formula_errors_in_text(
+                '<p>Simple variable: {x}.</p>'));
+        $this->assertFalse(qtype_calculated_find_formula_errors_in_text(
+                '<p>This is an equation: {=1+1}, as is this: {={x}+{y}}.</p>' .
+                '<p>Here is a more complex one: {=sin(2*pi()*{theta})}.</p>'));
+    }
+
+    public function test_validation_of_formulas_in_text_bad_function() {
+        $this->assert_nonempty_string(qtype_calculated_find_formula_errors_in_text(
+                '<p>This is an equation: {=eval(1)}.</p>'));
+        $this->assert_nonempty_string(qtype_calculated_find_formula_errors_in_text(
+                '<p>Good: {=1+1}, bad: {=eval(1)}, good: {={x}+{y}}.</p>'));
+        $this->assert_nonempty_string(qtype_calculated_find_formula_errors_in_text(
+                '<p>Bad: {=eval(1)}, bad: {=system(1)}.</p>'));
+    }
 }