Emit compile-time errors for conflicting modifiers.

sdk/lib/_internal/compiler/implementation/resolution/members.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 resolution;
 
 abstract class TreeElements {
   Element get currentElement;
   Set<Node> get superUses;
 
@@ skipping 2709 matching lines @@
                                        ElementKind.VARIABLE);
     // Ensure that we set the type of the [VariableListElement] since it depends
     // on the current scope. If the current scope is a [MethodScope] or
     // [BlockScope] it will not be available for the
     // [VariableListElement.computeType] method.
     if (node.type != null) {
       visitor.variables.type = resolveTypeAnnotation(node.type);
     } else {
       visitor.variables.type = compiler.types.dynamicType;
     }
+
+    Modifiers modifiers = node.modifiers;
+    void reportExtraModifier(String modifier) {
+      Node modifierNode;
+      for (var nodes = modifiers.nodes; !nodes.isEmpty; nodes = nodes.tail) {
+        if (modifier == nodes.head.asIdentifier().source.stringValue) {
+          modifierNode = nodes.head;
+          break;
+        }
+      }
+      assert(modifierNode != null);
+      compiler.reportError(modifierNode, MessageKind.EXTRANEOUS_MODIFIER,
+          {'modifier': modifier});
+    }
+    if (modifiers.isFinal() && (modifiers.isConst() || modifiers.isVar())) {
+      reportExtraModifier('final');
+    }
+    if (modifiers.isVar() && (modifiers.isConst() || node.type != null)) {
+      reportExtraModifier('var');
+    }
+
     visitor.visit(node.definitions);
   }
 
   visitWhile(While node) {
     visit(node.condition);
     visitLoopBodyIn(node, node.body, new BlockScope(scope));
   }
 
   visitParenthesizedExpression(ParenthesizedExpression node) {
     bool oldSendIsMemberAccess = sendIsMemberAccess;
@@ skipping 1606 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }