[poincare/parser] Comment and new test about system parentheses

poincare/src/parsing/parser.cpp

@@ -417,6 +417,9 @@ void Parser::parseCustomIdentifier(Expression & leftHandSide, const char * name,
     return;
   }
   bool poppedParenthesisIsSystem = false;
+  /* If the identifier is followed by parentheses it is a function, else it is a
+   * symbol. The parentheses can be system parentheses, if serialized using
+   * SerializationHelper::Prefix. */
   if (!popTokenIfType(Token::LeftParenthesis)) {
     if (!popTokenIfType(Token::LeftSystemParenthesis)) {
       leftHandSide = Symbol::Builder(name, length);
@@ -467,6 +470,8 @@ void Parser::parseIdentifier(Expression & leftHandSide, Token::Type stoppingType
 
 Expression Parser::parseFunctionParameters() {
   bool poppedParenthesisIsSystem = false;
+  /* The function parentheses can be system parentheses, if serialized using
+   * SerializationHelper::Prefix.*/
   if (!popTokenIfType(Token::LeftParenthesis)) {
     if (!popTokenIfType(Token::LeftSystemParenthesis)) {
       m_status = Status::Error; // Left parenthesis missing.

poincare/src/serialization_helper.cpp

@@ -80,6 +80,9 @@ int InfixPrefix(
 
   int numberOfChar = 0;
 
+  /* For Prefix, we use system parentheses so that, for instance, |3)+(1| is not
+   * parsable after serialization.*/
+
   if (prefix) {
     // Prefix: Copy the operator name
     numberOfChar = strlcpy(buffer, operatorName, bufferSize);

poincare/test/layouts.cpp

@@ -423,4 +423,18 @@ QUIZ_CASE(poincare_unparsable_layouts) {
         HorizontalLayout::Builder(children, childrenCount));
     assert_layout_is_not_parsed(l);
   }
+
+  {
+    // |3)+(1|
+    constexpr int childrenCount = 5;
+    Layout children[childrenCount] = {
+      CodePointLayout::Builder('3'),
+      RightParenthesisLayout::Builder(),
+      CodePointLayout::Builder('+'),
+      LeftParenthesisLayout::Builder(),
+      CodePointLayout::Builder('1')};
+
+    Layout l = AbsoluteValueLayout::Builder(HorizontalLayout::Builder(children, childrenCount));
+    assert_layout_is_not_parsed(l);
+  }
 }