LibJS: Memoize failed calls of try_parse_arrow_function_expression()

Author: https://github.com/sunverwerth
Commit: https://github.com/SerenityOS/serenity/commit/8c80eb8870f
Pull-request: https://github.com/SerenityOS/serenity/pull/6251
Issue: https://github.com/SerenityOS/serenity/issues/3349

Userland/Libraries/LibJS/Parser.cpp

@@ -627,11 +627,14 @@ NonnullRefPtr<Expression> Parser::parse_primary_expression()
 
     switch (m_parser_state.m_current_token.type()) {
     case TokenType::ParenOpen: {
+        auto paren_position = position();
         consume(TokenType::ParenOpen);
-        if (match(TokenType::ParenClose) || match(TokenType::Identifier) || match(TokenType::TripleDot)) {
+        if ((match(TokenType::ParenClose) || match(TokenType::Identifier) || match(TokenType::TripleDot)) && !try_parse_arrow_function_expression_failed_at_position(paren_position)) {
             auto arrow_function_result = try_parse_arrow_function_expression(true);
             if (!arrow_function_result.is_null())
                 return arrow_function_result.release_nonnull();
+
+            set_try_parse_arrow_function_expression_failed_at_position(paren_position, true);
         }
         auto expression = parse_expression(0);
         consume(TokenType::ParenClose);
@@ -651,9 +654,13 @@ NonnullRefPtr<Expression> Parser::parse_primary_expression()
             syntax_error("'super' keyword unexpected here");
         return create_ast_node<SuperExpression>({ m_parser_state.m_current_token.filename(), rule_start.position(), position() });
     case TokenType::Identifier: {
-        auto arrow_function_result = try_parse_arrow_function_expression(false);
-        if (!arrow_function_result.is_null())
-            return arrow_function_result.release_nonnull();
+        if (!try_parse_arrow_function_expression_failed_at_position(position())) {
+            auto arrow_function_result = try_parse_arrow_function_expression(false);
+            if (!arrow_function_result.is_null())
+                return arrow_function_result.release_nonnull();
+
+            set_try_parse_arrow_function_expression_failed_at_position(position(), true);
+        }
         return create_ast_node<Identifier>({ m_parser_state.m_current_token.filename(), rule_start.position(), position() }, consume().value());
     }
     case TokenType::NumericLiteral:
@@ -2039,6 +2046,20 @@ Position Parser::position() const
     };
 }
 
+bool Parser::try_parse_arrow_function_expression_failed_at_position(const Position& position) const
+{
+    auto it = m_token_memoizations.find(position);
+    if (it == m_token_memoizations.end())
+        return false;
+
+    return (*it).value.try_parse_arrow_function_expression_failed;
+}
+
+void Parser::set_try_parse_arrow_function_expression_failed_at_position(const Position& position, bool failed)
+{
+    m_token_memoizations.set(position, { failed });
+}
+
 void Parser::syntax_error(const String& message, Optional<Position> position)
 {
     if (!position.has_value())

Userland/Libraries/LibJS/Parser.h

@@ -147,6 +147,10 @@ public:
         }
     }
 
+    struct TokenMemoization {
+        bool try_parse_arrow_function_expression_failed;
+    };
+
 private:
     friend class ScopePusher;
 
@@ -172,6 +176,9 @@ private:
     void discard_saved_state();
     Position position() const;
 
+    bool try_parse_arrow_function_expression_failed_at_position(const Position&) const;
+    void set_try_parse_arrow_function_expression_failed_at_position(const Position&, bool);
+
     struct RulePosition {
         AK_MAKE_NONCOPYABLE(RulePosition);
         AK_MAKE_NONMOVABLE(RulePosition);
@@ -220,9 +227,23 @@ private:
         explicit ParserState(Lexer);
     };
 
+    class PositionKeyTraits {
+    public:
+        static int hash(const Position& position)
+        {
+            return int_hash(position.line) ^ int_hash(position.column);
+        }
+
+        static bool equals(const Position& a, const Position& b)
+        {
+            return a.column == b.column && a.line == b.line;
+        }
+    };
+
     Vector<Position> m_rule_starts;
     ParserState m_parser_state;
     FlyString m_filename;
     Vector<ParserState> m_saved_state;
+    HashMap<Position, TokenMemoization, PositionKeyTraits> m_token_memoizations;
 };
 }