Emit compile-time error for incorrectly used optional parameters.

sdk/lib/_internal/compiler/implementation/scanner/parser.dart

 // 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.
 
 part of scanner;
 
+class FormalParameterType {
+  final String type;
+  const FormalParameterType(this.type);
+  bool get isRequired => this == REQUIRED;
+  bool get isPositional => this == POSITIONAL;
+  bool get isNamed => this == NAMED;
+  static final REQUIRED = const FormalParameterType('required');
+  static final POSITIONAL = const FormalParameterType('positional');
+  static final NAMED = const FormalParameterType('named');
+}
+
 /**
  * An event generating parser of Dart programs. This parser expects
  * all tokens in a linked list (aka a token stream).
  *
  * The class [Scanner] is used to generate a token stream. See the
  * file scanner.dart.
  *
  * Subclasses of the class [Listener] are used to listen to events.
  *
  * Most methods of this class belong in one of two major categories:
@@ skipping 282 matching lines @@
       ++parameterCount;
       token = token.next;
       String value = token.stringValue;
       if (identical(value, '[')) {
         token = parseOptionalFormalParameters(token, false);
         break;
       } else if (identical(value, '{')) {
         token = parseOptionalFormalParameters(token, true);
         break;
       }
-      token = parseFormalParameter(token);
+      token = parseFormalParameter(token, FormalParameterType.REQUIRED);
     } while (optional(',', token));
     listener.endFormalParameters(parameterCount, begin, token);
     return expect(')', token);
   }
 
-  Token parseFormalParameter(Token token) {
+  Token parseFormalParameter(Token token, FormalParameterType type) {
     listener.beginFormalParameter(token);
     token = parseModifiers(token);
     // TODO(ahe): Validate that there are formal parameters if void.
     token = parseReturnTypeOpt(token);
     Token thisKeyword = null;
     if (optional('this', token)) {
       thisKeyword = token;
       // TODO(ahe): Validate field initializers are only used in
       // constructors, and not for function-typed arguments.
       token = expect('.', token.next);
     }
     token = parseIdentifier(token);
     if (optional('(', token)) {
       token = parseFormalParameters(token);
       listener.handleFunctionTypedFormalParameter(token);
     }
     String value = token.stringValue;
     if ((identical('=', value)) || (identical(':', value))) {
       // TODO(ahe): Validate that these are only used for optional parameters.
       Token equal = token;
       token = parseExpression(token.next);
       listener.handleValuedFormalParameter(equal, token);
+      if (type.isRequired) {
+        listener.reportError(equal,
+            MessageKind.REQUIRED_PARAMETER_WITH_DEFAULT);
+      } else if (type.isNamed && identical('=', value)) {
+        listener.reportError(equal, MessageKind.NAMED_PARAMETER_WITH_EQUALS);
+      } else if (type.isPositional && identical(':', value)) {
+        listener.reportError(equal,
+            MessageKind.POSITIONAL_PARAMETER_WITH_EQUALS);
+      }
     }
     listener.endFormalParameter(thisKeyword);
     return token;
   }
 
   Token parseOptionalFormalParameters(Token token, bool isNamed) {
     Token begin = token;
     listener.beginOptionalFormalParameters(begin);
     assert((isNamed && optional('{', token)) || optional('[', token));
     int parameterCount = 0;
     do {
       token = token.next;
-      token = parseFormalParameter(token);
+      var type = isNamed ? FormalParameterType.NAMED
+                         : FormalParameterType.POSITIONAL;
+      token = parseFormalParameter(token, type);
       ++parameterCount;
     } while (optional(',', token));
     listener.endOptionalFormalParameters(parameterCount, begin, token);
     if (isNamed) {
       return expect('}', token);
     } else {
       return expect(']', token);
     }
   }
 
@@ skipping 2018 matching lines @@
     }
     listener.handleContinueStatement(hasTarget, continueKeyword, token);
     return expectSemicolon(token);
   }
 
   Token parseEmptyStatement(Token token) {
     listener.handleEmptyStatement(token);
     return expectSemicolon(token);
   }
 }