Add compilation error on named parameters with private names

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 "lib/invocation_mirror.h"
 #include "vm/bigint_operations.h"
 #include "vm/bootstrap.h"
 #include "vm/class_finalizer.h"
@@ skipping 1392 matching lines @@
     parameter.is_field_initializer = true;
   }
 
   // At this point, we must see an identifier for the parameter name.
   parameter.name_pos = TokenPos();
   parameter.name = ExpectIdentifier("parameter name expected");
   if (parameter.is_field_initializer) {
     params->has_field_initializer = true;
   }
 
+  if (params->has_optional_named_parameters &&
+      (parameter.name->CharAt(0) == '_')) {
+    ErrorMsg(parameter.name_pos, "named parameter must not be private");
+  }
+
   // Check for duplicate formal parameters.
   const intptr_t num_existing_parameters =
       params->num_fixed_parameters + params->num_optional_parameters;
   for (intptr_t i = 0; i < num_existing_parameters; i++) {
     ParamDesc& existing_parameter = (*params->parameters)[i];
     if (existing_parameter.name->Equals(*parameter.name)) {
       ErrorMsg(parameter.name_pos, "duplicate formal parameter '%s'",
                parameter.name->ToCString());
     }
   }
@@ skipping 8997 matching lines @@
 void Parser::SkipQualIdent() {
   ASSERT(IsIdentifier());
   ConsumeToken();
   if (CurrentToken() == Token::kPERIOD) {
     ConsumeToken();  // Consume the kPERIOD token.
     ExpectIdentifier("identifier expected after '.'");
   }
 }
 
 }  // namespace dart