Better error reporting for "return();"

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 484 matching lines @@
   }
 
   void ReportMessageAt(Scanner::Location location,
                        MessageTemplate::Template 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);
+  void ReportUnexpectedTokenAt(
+      Scanner::Location location, Token::Value token,
+      MessageTemplate::Template message = MessageTemplate::kUnexpectedToken);
 
 
   void ReportClassifierError(const ExpressionClassifier::Error& error) {
     Traits::ReportMessageAt(error.location, error.message, error.arg,
                             kSyntaxError);
   }
 
   void ValidateExpression(const ExpressionClassifier* classifier, bool* ok) {
     if (!classifier->is_valid_expression()) {
       ReportClassifierError(classifier->expression_error());
@@ skipping 1291 matching lines @@
   *function_state_stack_ = outer_function_state_;
 }
 
 
 template<class Traits>
 void ParserBase<Traits>::ReportUnexpectedToken(Token::Value token) {
   return ReportUnexpectedTokenAt(scanner_->location(), token);
 }
 
 
-template<class Traits>
+template <class Traits>
 void ParserBase<Traits>::ReportUnexpectedTokenAt(
-    Scanner::Location source_location, Token::Value token) {
-
+    Scanner::Location source_location, Token::Value token,
+    MessageTemplate::Template message) {
   // Four of the tokens are treated specially
   switch (token) {
     case Token::EOS:
       return ReportMessageAt(source_location, MessageTemplate::kUnexpectedEOS);
     case Token::SMI:
     case Token::NUMBER:
       return ReportMessageAt(source_location,
                              MessageTemplate::kUnexpectedTokenNumber);
     case Token::STRING:
       return ReportMessageAt(source_location,
@@ skipping 12 matching lines @@
                              is_strict(language_mode())
                                  ? MessageTemplate::kUnexpectedStrictReserved
                                  : MessageTemplate::kUnexpectedTokenIdentifier);
     case Token::TEMPLATE_SPAN:
     case Token::TEMPLATE_TAIL:
       return Traits::ReportMessageAt(
           source_location, MessageTemplate::kUnexpectedTemplateString);
     default:
       const char* name = Token::String(token);
       DCHECK(name != NULL);
-      Traits::ReportMessageAt(source_location,
-                              MessageTemplate::kUnexpectedToken, name);
+      Traits::ReportMessageAt(source_location, message, name);
   }
 }
 
 
 template <class Traits>
 typename ParserBase<Traits>::IdentifierT ParserBase<Traits>::ParseIdentifier(
     AllowRestrictedIdentifiers allow_restricted_identifiers, bool* ok) {
   ExpressionClassifier classifier;
   auto result = ParseAndClassifyIdentifier(&classifier, ok);
   if (!*ok) return Traits::EmptyIdentifier();
@@ skipping 280 matching lines @@
       if (!classifier->is_valid_binding_pattern()) {
         ArrowFormalParametersUnexpectedToken(classifier);
       }
       BindingPatternUnexpectedToken(classifier);
       Consume(Token::LPAREN);
       if (allow_harmony_arrow_functions() && Check(Token::RPAREN)) {
         // As a primary expression, the only thing that can follow "()" is "=>".
         classifier->RecordBindingPatternError(scanner()->location(),
                                               MessageTemplate::kUnexpectedToken,
                                               Token::String(Token::RPAREN));
+        // Give a good error to the user who might have typed e.g. "return();".
+        if (peek() != Token::ARROW) {
+          ReportUnexpectedTokenAt(scanner_->peek_location(), peek(),
+                                  MessageTemplate::kMissingArrow);
+          *ok = false;
+          return this->EmptyExpression();
+        }
         Scope* scope =
             this->NewScope(scope_, ARROW_SCOPE, FunctionKind::kArrowFunction);
         scope->set_start_position(beg_pos);
         ExpressionClassifier args_classifier;
         bool has_rest = false;
         result = this->ParseArrowFunctionLiteral(scope, has_rest,
                                                  args_classifier, CHECK_OK);
       } else if (allow_harmony_arrow_functions() &&
                  allow_harmony_rest_params() && Check(Token::ELLIPSIS)) {
         // (...x) => y
@@ skipping 1699 matching lines @@
       *ok = false;
       return;
     }
     has_seen_constructor_ = true;
     return;
   }
 }
 } }  // v8::internal
 
 #endif  // V8_PREPARSER_H