LibJS: Support LegacyOctalEscapeSequence in string literals

https://tc39.es/ecma262/#sec-additional-syntax-string-literals

The syntax and semantics of 11.8.4 is extended as follows except that
this extension is not allowed for strict mode code:

Syntax

    EscapeSequence::
        CharacterEscapeSequence
        LegacyOctalEscapeSequence
        NonOctalDecimalEscapeSequence
        HexEscapeSequence
        UnicodeEscapeSequence

    LegacyOctalEscapeSequence::
        OctalDigit [lookahead ∉ OctalDigit]
        ZeroToThree OctalDigit [lookahead ∉ OctalDigit]
        FourToSeven OctalDigit
        ZeroToThree OctalDigit OctalDigit

    ZeroToThree :: one of
        0 1 2 3

    FourToSeven :: one of
        4 5 6 7

    NonOctalDecimalEscapeSequence :: one of
        8 9

This definition of EscapeSequence is not used in strict mode or when
parsing TemplateCharacter.

Note

It is possible for string literals to precede a Use Strict Directive
that places the enclosing code in strict mode, and implementations must
take care to not use this extended definition of EscapeSequence with
such literals. For example, attempting to parse the following source
text must fail:

function invalid() { "\7"; "use strict"; }

1 files changed, 2 insertions, 1 deletions

diff --git a/Libraries/LibJS/Parser.h b/Libraries/LibJS/Parser.h
index 007e8b6879..565f3ff704 100644
--- a/Libraries/LibJS/Parser.h
+++ b/Libraries/LibJS/Parser.h
@@ -87,7 +87,7 @@ public:
     NonnullRefPtr<RegExpLiteral> parse_regexp_literal();
     NonnullRefPtr<ObjectExpression> parse_object_expression();
     NonnullRefPtr<ArrayExpression> parse_array_expression();
-    NonnullRefPtr<StringLiteral> parse_string_literal(Token token);
+    NonnullRefPtr<StringLiteral> parse_string_literal(Token token, bool in_template_literal = false);
     NonnullRefPtr<TemplateLiteral> parse_template_literal(bool is_tagged);
     NonnullRefPtr<Expression> parse_secondary_expression(NonnullRefPtr<Expression>, int min_precedence, Associativity associate = Associativity::Right);
     NonnullRefPtr<CallExpression> parse_call_expression(NonnullRefPtr<Expression>);
@@ -184,6 +184,7 @@ private:
         bool m_in_function_context { false };
         bool m_in_break_context { false };
         bool m_in_continue_context { false };
+        bool m_string_legacy_octal_escape_sequence_in_scope { false };
 
         explicit ParserState(Lexer);
     };