Fix #574: Wrong error highlighting with interface implementation

src/Libraries/NRefactory/ICSharpCode.NRefactory.CSharp.Refactoring/CodeActions/ImplementInterfaceAction.cs

@@ -131,8 +131,8 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 						continue;
 
 					bool needsExplicitly = explicitly;
-					alreadyImplemented = implementingType.GetMembers().Any(m => m.ImplementedInterfaceMembers.Any(im => IsImplementation (im, ev)));
-				
+					var implementingMember = implementingType.GetInterfaceImplementation(ev);
+					alreadyImplemented = (implementingMember != null);
 					if (!alreadyImplemented) {
 						toImplement.Add(new Tuple<IMember, bool>(ev, needsExplicitly));
 					} else {
@@ -148,16 +148,17 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 					bool needsExplicitly = explicitly;
 					alreadyImplemented = false;
 					
-					foreach (var cmet in implementingType.GetMethods ()) {
-						alreadyImplemented |= cmet.ImplementedInterfaceMembers.Any(m => IsImplementation (m, method));
-
-						if (CompareMembers(method, cmet)) {
-							if (!needsExplicitly && !cmet.ReturnType.Equals(method.ReturnType))
-								needsExplicitly = true;
-							else
-								alreadyImplemented |= !needsExplicitly /*|| cmet.InterfaceImplementations.Any (impl => impl.InterfaceType.Equals (interfaceType))*/;
+					var implementingMethod = implementingType.GetInterfaceImplementation(method);
+					alreadyImplemented = (implementingMethod != null);
+					if (alreadyImplemented) {
+						if (!needsExplicitly && !implementingMethod.ReturnType.Equals(method.ReturnType)) {
+							needsExplicitly = true;
+							alreadyImplemented = false;
+						} else {
+							alreadyImplemented = !needsExplicitly;
 						}
 					}
+					
 					if (toImplement.Where(t => t.Item1 is IMethod).Any(t => CompareMembers(method, (IMethod)t.Item1)))
 						needsExplicitly = true;
 					if (!alreadyImplemented) {
@@ -174,27 +175,18 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 						continue;
 
 					bool needsExplicitly = explicitly;
-					alreadyImplemented = implementingType.GetMembers().Any(m => m.ImplementedInterfaceMembers.Any(im => IsImplementation (im, prop)));
-
-					foreach (var t in implementingType.GetAllBaseTypeDefinitions ()) {
-						if (t.Kind == TypeKind.Interface) {
-							foreach (var cprop in t.Properties) {
-								if (cprop.Name == prop.Name && cprop.IsShadowing) {
-									if (!needsExplicitly && !cprop.ReturnType.Equals(prop.ReturnType))
-										needsExplicitly = true;
-								}
-							}
-							continue;
-						}
-						foreach (var cprop in t.Properties) {
-							if (cprop.Name == prop.Name) {
-								if (!needsExplicitly && !cprop.ReturnType.Equals(prop.ReturnType))
-									needsExplicitly = true;
-								else
-									alreadyImplemented |= !needsExplicitly/* || cprop.InterfaceImplementations.Any (impl => impl.InterfaceType.Resolve (ctx).Equals (interfaceType))*/;
-							}
+					
+					var implementingProp = implementingType.GetInterfaceImplementation(prop);
+					alreadyImplemented = (implementingProp != null);
+					if (alreadyImplemented) {
+						if (!needsExplicitly && !implementingProp.ReturnType.Equals(prop.ReturnType)) {
+							needsExplicitly = true;
+							alreadyImplemented = false;
+						} else {
+							alreadyImplemented = !needsExplicitly;
 						}
 					}
+					
 					if (!alreadyImplemented) {
 						toImplement.Add(new Tuple<IMember, bool>(prop, needsExplicitly));
 					} else {