allow degree symbol as unit (#285)

Author: PhilippImhof

classes/local/evaluator.php

@@ -365,8 +365,8 @@ private function set_variable_to_value(token $vartoken, token $value, $definingr
             $basename = strstr($basename, '[', true);
         }
 
-        // We do not allow Ω and µ in variable names.
-        $isunit = preg_match('/[\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $basename);
+        // We do not allow °, Ω and µ in variable names.
+        $isunit = preg_match('/[°\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $basename);
         if ($isunit) {
             $this->die(get_string('error_invalidvarname', 'qtype_formulas', $basename), $value);
         }

classes/local/lexer.php

@@ -109,8 +109,8 @@ private function read_next_token(): ?token {
         }
         // A letter indicates the start of an identifier, i. e. a variable or function name.
         // We also accept U+00B5 (MICRO SIGN), U+03BC (GREEK SMALL MU), U+2126 (OHM) and
-        // U+03A9 (GREEK CAPITAL OMEGA) for units.
-        if (preg_match('/[_A-Za-z\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $currentchar)) {
+        // U+03A9 (GREEK CAPITAL OMEGA) for units. And we allow the degree symbol ° as well.
+        if (preg_match('/[_A-Za-z°\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $currentchar)) {
             return $this->read_identifier();
         }
         // Unless we are in the middle of a ternary operator, we treat : as a RANGE_SEPARATOR.
@@ -426,10 +426,11 @@ private function read_identifier(): token {
         while ($currentchar !== input_stream::EOF) {
             $nextchar = $this->inputstream->peek();
             // Identifiers may contain letters, digits or underscores. Also, we will accept the
-            // µ and Ω symbols, because they may appear in units. We don't want to throw lexing
-            // errors while reading them. Note that we explicitly include U+00B5 (MICRO SIGN),
-            // U+03BC (GREEK SMALL MU), U+2126 (OHM) and U+03A9 (GREEK CAPITAL OMEGA).
-            if (!preg_match('/[A-Za-z0-9_\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $nextchar)) {
+            // µ and Ω symbols, because they may appear in units. The same is true for the degree °
+            // symbol. We don't want to throw lexing errors while reading them. Note that we
+            // explicitly include U+00B5 (MICRO SIGN), U+03BC (GREEK SMALL MU), U+2126 (OHM) and
+            // U+03A9 (GREEK CAPITAL OMEGA).
+            if (!preg_match('/[A-Za-z°0-9_\x{00B5}\x{03BC}\x{03A9}\x{2126}]/u', $nextchar)) {
                 break;
             }
             $currentchar = $this->inputstream->read();

tests/answer_parser_test.php

@@ -314,6 +314,8 @@ public static function provide_numbers_and_units(): array {
             'MICRO SIGN' => [['1', 'µs'], '1 µs'],
             'percent with space' => [['5', '%'], '5 %'],
             'percent without space' => [['5', '%'], '5%'],
+            'degree with space' => [['5', '°'], '5 °'],
+            'degree without space' => [['5', '°'], '5°'],
 
             [['.3', ''], '.3'],
             [['3.1', ''], '3.1'],

tests/evaluator_test.php

@@ -1842,6 +1842,18 @@ public static function provide_invalid_assignments(): array {
                 'Invalid variable name: kΩ.',
                 'kΩ = 2',
             ],
+            'invalid variable, degree alone' => [
+                'Invalid variable name: °.',
+                '° = 2',
+            ],
+            'invalid variable, degree at start' => [
+                'Invalid variable name: °x.',
+                '°x = 2',
+            ],
+            'invalid variable, degree in name' => [
+                'Invalid variable name: k°.',
+                'k° = 2',
+            ],
             'invalid assignment with % at end' => [
                 "Syntax error: unexpected end of expression after '%'.",
                 'a = 2 %',

tests/questiontype_test.php

@@ -312,6 +312,7 @@ public static function provide_single_part_data_for_form_validation(): array {
             [[], ['answer' => [0 => '\sin(20)']]],
             [[], ['answer' => [0 => '[1, 2]']]],
             [[], ['answer' => [0 => '0']]],
+            [[], ['answer' => [0 => '5'], 'postunit' => [0 => '°']]],
             [[], ['answer' => [0 => '5'], 'postunit' => [0 => '%']]],
             [[], ['answer' => [0 => '1'], 'postunit' => [0 => 'Ω']]],
             [[], ['answer' => [0 => '1'], 'postunit' => [0 => 'µs']]],

tests/walkthrough_adaptive_test.php

@@ -986,6 +986,21 @@ public function test_combined_field_with_percent(): void {
         $this->check_current_mark(1);
     }
 
+    public function test_combined_field_with_degree(): void {
+        // Create a question.
+        $q = $this->get_test_formulas_question('testsinglenumunit');
+        $q->parts[0]->answer = '5';
+        $q->parts[0]->postunit = '°';
+
+        // Start an attempt and submit various correct answers.
+        $this->start_attempt_at_question($q, 'immediatefeedback', 1);
+        $this->process_submission(['0_' => '5 °', '-submit' => 1]);
+        $this->check_current_mark(1);
+        $this->start_attempt_at_question($q, 'immediatefeedback', 1);
+        $this->process_submission(['0_' => '5°', '-submit' => 1]);
+        $this->check_current_mark(1);
+    }
+
     public function test_combined_field_with_ohm(): void {
         // Create a question.
         $q = $this->get_test_formulas_question('testsinglenumunit');