Implement override checks.

dart/lib/compiler/implementation/resolver.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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   Type getType(TypeAnnotation annotation);
 }
 
@@ skipping 211 matching lines @@
   }
 
   void resolveClass(ClassElement element) {
     if (element.isResolved) return;
     measure(() {
       ClassNode tree = element.parseNode(compiler);
       ClassResolverVisitor visitor =
         new ClassResolverVisitor(compiler, element.getLibrary(), element);
       visitor.visit(tree);
       element.isResolved = true;
+
+      while (!toResolve.isEmpty()) {
+        ClassElement classElement = toResolve.removeFirst();
+        classElement.ensureResolved(compiler);
+      }
+
+      checkOverrides(element);
     });
   }
 
+  checkOverrides(ClassElement cls) {
+    if (cls === compiler.objectClass) return;
+    cls.forEachMember((holder, member) {
+      Element superMember = cls.lookupSuperMember(member.name);
+      if (superMember !== null) {
+        if (member.modifiers.isStatic()) {
+          compiler.cancel('Static members cannot override', element: member);
+        } else {
+          FunctionElement superFunction = superMember.asFunctionElement();
+          FunctionElement function = member.asFunctionElement();
+          if (superFunction === null || superFunction.isAccessor()) {
+            // Field or accessor in super.
+            if (function !== null && !function.isAccessor()) {
+              // But a plain method in this class.
+              compiler.cancel('Cannot override field with method',
+                              element: member);
+            }
+          } else {
+            // Instance method in super.
+            if (function === null || function.isAccessor()) {
+              // But a field in this class.

[karlklose, 2012/06/20 13:51:31]

... or accessor ...?

[ahe, 2012/06/22 12:50:33]

Done.

+              compiler.cancel('Cannot override method with field',
+                              element: member);
+            } else {
+              // Both are plain instance methods.
+              if (superFunction.requiredParameterCount(compiler) !=
+                  function.requiredParameterCount(compiler)) {
+                compiler.cancel('Bad override', element: member);
+              }
+              // TODO(ahe): Check optional parameters.
+            }
+          }
+        }
+      }
+    });
+  }
+
   FunctionSignature resolveSignature(FunctionElement element) {
     return compiler.withCurrentElement(element, () {
       FunctionExpression node =
           compiler.parser.measure(() => element.parseNode(compiler));
       return measure(() => SignatureResolver.analyze(
           compiler, node.parameters, node.returnType, element));
     });
   }
 
   FunctionSignature resolveTypedef(TypedefElement element) {
@@ skipping 1848 matching lines @@
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) {
     return library.find(name);
   }
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
 }