Warn when implicit default value overrides explicit one that differs.

pkg/analyzer/lib/src/generated/error_verifier.dart

 // Copyright (c) 2014, 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.
 
 library engine.resolver.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'java_engine.dart';
@@ skipping 1341 matching lines @@
         for (int i = 0; i < parameterElts.length; i++) {
           ParameterElementImpl parameterElt = parameterElts[i];
           EvaluationResultImpl result = parameterElt.evaluationResult;
           // TODO (jwren) Ignore Object types, see Dart bug 11287
           if (_isUserDefinedObject(result)) {
             continue;
           }
           String parameterName = parameterElt.name;
           for (int j = 0; j < overriddenParameterElts.length; j++) {
             ParameterElementImpl overriddenParameterElt = overriddenParameterElts[j];
+            if (overriddenParameterElt.initializer == null) {
+              // There is no warning if the overridden parameter has an
+              // implicit default.
+              continue;
+            }
             String overriddenParameterName = overriddenParameterElt.name;
             if (parameterName != null && parameterName == overriddenParameterName) {
               EvaluationResultImpl overriddenResult = overriddenParameterElt.evaluationResult;
               if (_isUserDefinedObject(overriddenResult)) {
                 break;
               }
               if (!result.equalValues(_typeProvider, overriddenResult)) {
                 _errorReporter.reportErrorForNode(StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_NAMED, formalParameters[i], [
                     overriddenExecutable.enclosingElement.displayName,
                     overriddenExecutable.displayName,
                     parameterName]);
                 foundError = true;
               }
             }
           }
         }
       } else {
         // Positional parameters, consider the positions when matching the parameterElts to the overriddenParameterElts
         for (int i = 0; i < parameterElts.length && i < overriddenParameterElts.length; i++) {
           ParameterElementImpl parameterElt = parameterElts[i];
           EvaluationResultImpl result = parameterElt.evaluationResult;
           // TODO (jwren) Ignore Object types, see Dart bug 11287
           if (_isUserDefinedObject(result)) {
             continue;
           }
           ParameterElementImpl overriddenParameterElt = overriddenParameterElts[i];
+          if (overriddenParameterElt.initializer == null) {
+            // There is no warning if the overridden parameter has an implicit
+            // default.
+            continue;
+          }
           EvaluationResultImpl overriddenResult = overriddenParameterElt.evaluationResult;
           if (_isUserDefinedObject(overriddenResult)) {
             continue;
           }
           if (!result.equalValues(_typeProvider, overriddenResult)) {
             _errorReporter.reportErrorForNode(StaticWarningCode.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_POSITIONAL, formalParameters[i], [
                 overriddenExecutable.enclosingElement.displayName,
                 overriddenExecutable.displayName]);
             foundError = true;
           }
@@ skipping 4091 matching lines @@
     toCheck.add(element);
     // type arguments
     if (type is InterfaceType) {
       InterfaceType interfaceType = type;
       for (DartType typeArgument in interfaceType.typeArguments) {
         _addTypeToCheck(typeArgument);
       }
     }
   }
 }