Add parser support for generators.

src/preparser.cc

Index: src/preparser.cc
diff --git a/src/preparser.cc b/src/preparser.cc
index 21da4f80d418cb31d6d9e1c8bdbd4e3972d6be5e..ad162ed2666b1274277cdec1f6666537cc178f36 100644
--- a/src/preparser.cc
+++ b/src/preparser.cc
@@ -1119,6 +1119,16 @@ PreParser::Expression PreParser::ParsePrimaryExpression(bool* ok) {
       return Expression::Default();
     }
 
+      // FIXME!!!!
+    case i::Token::YIELD:

[wingo, 2013/03/11 12:10:53]

This FIXME is to mark that this case and the FUTURE_RESERVED_WORD case and the
FUTURE_STRICT_RESERVED_WORD case can all be elided, it seems, as ParseIdentifier
(called later) will DTRT.  Am preparing a patch for that.  Apologies for letting
a FIXME through :)

+      if (scope_->is_generator()) {
+        // 'yield' in a generator is only valid as part of a YieldExpression.
+        i::Scanner::Location location = scanner_->location();
+        ReportMessageAt(location, "unexpected_token", NULL);
+        *ok = false;
+        return Expression::Default();
+      }
+      // FALLTHROUGH
     case i::Token::FUTURE_STRICT_RESERVED_WORD:
       if (!is_classic_mode()) {
         Next();
@@ -1513,6 +1523,8 @@ PreParser::Identifier PreParser::GetIdentifierSymbol() {
   } else if (scanner_->current_token() ==
              i::Token::FUTURE_STRICT_RESERVED_WORD) {
     return Identifier::FutureStrictReserved();
+  } else if (scanner_->current_token() == i::Token::YIELD) {
+    return Identifier::Yield();
   }
   if (scanner_->is_literal_ascii()) {
     // Detect strict-mode poison words.
@@ -1539,6 +1551,16 @@ PreParser::Identifier PreParser::ParseIdentifier(bool* ok) {
       *ok = false;
       return GetIdentifierSymbol();
     }
+    case i::Token::YIELD:
+      if (scope_->is_generator()) {
+        // 'yield' in a generator is only valid as part of a YieldExpression.
+        i::Scanner::Location location = scanner_->location();
+        ReportMessageAt(location.beg_pos, location.end_pos,
+                        "unexpected_token", NULL);
+        *ok = false;
+        return Identifier::Default();
+      }
+      // FALLTHROUGH
     case i::Token::FUTURE_STRICT_RESERVED_WORD:
       if (!is_classic_mode()) {
         i::Scanner::Location location = scanner_->location();
@@ -1596,7 +1618,7 @@ void PreParser::StrictModeIdentifierViolation(i::Scanner::Location location,
   const char* type = eval_args_type;
   if (identifier.IsFutureReserved()) {
     type = "reserved_word";
-  } else if (identifier.IsFutureStrictReserved()) {
+  } else if (identifier.IsFutureStrictReserved() || identifier.IsYield()) {
     type = "strict_reserved_word";
   }
   if (!is_classic_mode()) {