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LibJS: Parse secondary expressions with the original forbidden token set

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Instead of passing the continuously merged initial forbidden token set
(with the new additional forbidden tokens from each parsed secondary
expression) to the next call of parse_secondary_expression(), keep a
copy of the original set and use it as the base for parsing the next
secondary expression.

This bug prevented us from properly parsing the following expression:

```js
0 ?? 0 ? 0 : 0 || 0
```

...due to LogicalExpression with LogicalOp::NullishCoalescing returning
both DoubleAmpersand and DoublePipe in its forbidden token set.

The following correct AST is now generated:

Program
  (Children)
    ExpressionStatement
      ConditionalExpression
        (Test)
          LogicalExpression
            NumericLiteral 0
            ??
            NumericLiteral 0
        (Consequent)
          NumericLiteral 0
        (Alternate)
          LogicalExpression
            NumericLiteral 0
            ||
            NumericLiteral 0

An alternate solution I explored was only merging the original forbidden
token set with the one of the last parsed secondary expression which is
then passed to match_secondary_expression(); however that led to an
incorrect AST (note the alternate expression):

Program
  (Children)
    ExpressionStatement
      LogicalExpression
        ConditionalExpression
          (Test)
            LogicalExpression
              NumericLiteral 0
              ??
              NumericLiteral 0
          (Consequent)
            NumericLiteral 0
          (Alternate)
            NumericLiteral 0
        ||
        NumericLiteral 0

Truth be told, I don't know enough about the inner workings of the
parser to fully explain the difference. AFAICT this patch has no
unintended side effects in its current form though.

Fixes #18087.
This commit is contained in:
Linus Groh
2023-04-01 20:44:32 +01:00
committed by Andreas Kling
parent 85d0637058
commit 3709d11212
2 changed files with 15 additions and 1 deletions
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3
Userland/Libraries/LibJS/Parser.cpp
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@@ -2001,6 +2001,7 @@ NonnullRefPtr<Expression const> Parser::parse_expression(int min_precedence, Ass
expression = create_ast_node<TaggedTemplateLiteral>({ m_source_code, rule_start.position(), position() }, move(expression), move(template_literal));
}
if (should_continue_parsing) {
auto original_forbidden = forbidden;
while (match_secondary_expression(forbidden)) {
int new_precedence = g_operator_precedence.get(m_state.current_token.type());
if (new_precedence < min_precedence)
@@ -2010,7 +2011,7 @@ NonnullRefPtr<Expression const> Parser::parse_expression(int min_precedence, Ass
check_for_invalid_object_property(expression);
Associativity new_associativity = operator_associativity(m_state.current_token.type());
auto result = parse_secondary_expression(move(expression), new_precedence, new_associativity, forbidden);
auto result = parse_secondary_expression(move(expression), new_precedence, new_associativity, original_forbidden);
expression = result.expression;
forbidden = forbidden.merge(result.forbidden);
while (match(TokenType::TemplateLiteralStart) && !is<UpdateExpression>(*expression)) {