Better error reporting for "return();"

R=rossberg@chromium.org
BUG=v8:4194
LOG=N

Review URL: https://codereview.chromium.org/1191303002

Cr-Commit-Position: refs/heads/master@{#29153}

src/messages.h

@@ -323,6 +323,8 @@ class CallSite {
   T(MalformedArrowFunParamList, "Malformed arrow function parameter list")     \
   T(MalformedRegExp, "Invalid regular expression: /%/: %")                     \
   T(MalformedRegExpFlags, "Invalid regular expression flags")                  \
+  T(MissingArrow,                                                              \
+    "Expected () to start arrow function, but got '%' instead of '=>'")        \
   T(ModuleExportUndefined, "Export '%' is not defined in module")              \
   T(MultipleDefaultsInSwitch,                                                  \
     "More than one default clause in switch statement")                        \

src/preparser.h

@@ -502,7 +502,9 @@ class ParserBase : public Traits {
   }
 
   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) {
@@ -1814,10 +1816,10 @@ void ParserBase<Traits>::ReportUnexpectedToken(Token::Value 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:
@@ -1850,8 +1852,7 @@ void ParserBase<Traits>::ReportUnexpectedTokenAt(
     default:
       const char* name = Token::String(token);
       DCHECK(name != NULL);
-      Traits::ReportMessageAt(source_location,
-                              MessageTemplate::kUnexpectedToken, name);
+      Traits::ReportMessageAt(source_location, message, name);
   }
 }
 
@@ -2152,6 +2153,13 @@ ParserBase<Traits>::ParsePrimaryExpression(ExpressionClassifier* classifier,
         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);

test/message/arrow-missing.js

+// Copyright 2015 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.
+//
+// Flags: --harmony-rest-parameters --harmony-arrow-functions
+
+function foo() { return(); }

test/message/arrow-missing.out

+*%(basename)s:7: SyntaxError: Expected () to start arrow function, but got ';' instead of '=>'
+function foo() { return(); }
+                         ^
+SyntaxError: Expected () to start arrow function, but got ';' instead of '=>'