[parser] parse arrow function only if no linefeed before =>

src/preparser.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_PREPARSER_H
 #define V8_PREPARSER_H
 
 #include "src/v8.h"
 
 #include "src/bailout-reason.h"
@@ skipping 520 matching lines @@
     Traits::ReportMessageAt(source_location, message, arg, error_type);
   }
 
   void ReportMessageAt(Scanner::Location location, const char* message,
                        ParseErrorType error_type = kSyntaxError) {
     Traits::ReportMessageAt(location, message, reinterpret_cast<const char*>(0),
                             error_type);
   }
 
   void ReportUnexpectedToken(Token::Value token);
+  void ReportUnexpectedTokenAt(Scanner::Location location, Token::Value token);
 
   // Recursive descent functions:
 
   // Parses an identifier that is valid for the current scope, in particular it
   // fails on strict mode future reserved keywords in a strict scope. If
   // allow_eval_or_arguments is kAllowEvalOrArguments, we allow "eval" or
   // "arguments" as identifier even in strict mode (this is needed in cases like
   // "var foo = eval;").
   IdentifierT ParseIdentifier(
       AllowEvalOrArgumentsAsIdentifier,
@@ skipping 1123 matching lines @@
 
 template <class Traits>
 ParserBase<Traits>::FunctionState::~FunctionState() {
   *scope_stack_ = outer_scope_;
   *function_state_stack_ = outer_function_state_;
 }
 
 
 template<class Traits>
 void ParserBase<Traits>::ReportUnexpectedToken(Token::Value token) {
-  Scanner::Location source_location = scanner()->location();
+  return ReportUnexpectedTokenAt(scanner_->location(), token);
+}
+
+
+template<class Traits>
+void ParserBase<Traits>::ReportUnexpectedTokenAt(
+    Scanner::Location source_location, Token::Value token) {
 
   // Four of the tokens are treated specially
   switch (token) {
     case Token::EOS:
       return ReportMessageAt(source_location, "unexpected_eos");
     case Token::SMI:
     case Token::NUMBER:
       return ReportMessageAt(source_location, "unexpected_token_number");
     case Token::STRING:
       return ReportMessageAt(source_location, "unexpected_token_string");
@@ skipping 1144 matching lines @@
   DCHECK(false);
   return this->EmptyExpression();
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::ExpressionT
 ParserBase<Traits>::ParseArrowFunctionLiteral(int start_pos,
                                               ExpressionT params_ast,
                                               bool* ok) {
+  if (peek() == Token::ARROW && scanner_->HasAnyLineTerminatorBeforeNext()) {
+    // ASI inserts `;` after arrow parameters if a line terminator is found.
+    // `=> ...` is never a valid expression, so report as syntax error.
+    // If next token is not `=>`, it's a syntax error anyways.
+    ReportUnexpectedTokenAt(scanner_->peek_location(), Token::ARROW);
+    *ok = false;
+    return this->EmptyExpression();
+  }
+
   Scope* scope = this->NewScope(scope_, ARROW_SCOPE);
   typename Traits::Type::StatementList body;
   int num_parameters = -1;
   int materialized_literal_count = -1;
   int expected_property_count = -1;
   int handler_count = 0;
 
   {
     typename Traits::Type::Factory function_factory(ast_value_factory());
     FunctionState function_state(&function_state_, &scope_, scope,
@@ skipping 257 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H