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LibJS: Check AssignmentExpression LHS in parser

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There are many cases which shouldn't even parse, like

null = ...
true = ...
false = ...
123 = ...
"foo" = ...

However this *is* valid syntax:

foo() = ...

So we still have to keep the current code doing a runtime check if the
LHS value is a resolvable reference. I believe this was declared valid
syntax to *in theory* allow functions returning references - though in
practice that isn't a thing.

Fixes #2204.
This commit is contained in:
Linus Groh 2020-05-12 21:19:48 +01:00 • committed by Andreas Kling
parent 063228c02e
commit d69ed91790
3 changed files with 11 additions and 9 deletions
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4
Libraries/LibJS/Parser.cpp
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@ -755,6 +755,10 @@ NonnullRefPtr<Expression> Parser::parse_secondary_expression(NonnullRefPtr<Expre
return parse_call_expression(move(lhs));
case TokenType::Equals:
consume();
if (!lhs->is_identifier() && !lhs->is_member_expression() && !lhs->is_call_expression()) {
syntax_error("Invalid left-hand side in assignment");
return create_ast_node<ErrorExpression>();
}
return create_ast_node<AssignmentExpression>(AssignmentOp::Assignment, move(lhs), parse_expression(min_precedence, associativity));
case TokenType::Period:
consume();