named optional parameters must not be private

runtime/vm/parser.cc

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/parser.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/compiler_stats.h"
@@ skipping 875 matching lines @@
   if (!this_seen && (CurrentToken() == Token::kTHIS)) {
     ConsumeToken();
     ExpectToken(Token::kPERIOD);
     this_seen = true;
     parameter.is_field_initializer = true;
   }
 
   // At this point, we must see an identifier for the parameter name.
   parameter.name_pos = token_index_;
   parameter.name = ExpectIdentifier("parameter name expected");
+  if (params->has_named_optional_parameters &&
+      (parameter.name->CharAt(0) == '_')) {
+    ErrorMsg(parameter.name_pos,
+             "named optional parameters may not start with '_'\n");
+  }
 
   if (parameter.is_field_initializer) {
     params->has_field_initializer = true;
   }
 
   if (CurrentToken() == Token::kLPAREN) {
     // This parameter is probably a closure. If we saw the keyword 'var'
     // or 'final', a closure is not legal here and we ignore the
     // opening parens.
     if (!var_seen && !parameter.is_final) {
@@ skipping 7301 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart