Emit a warning and runtime error when assigning to a function.

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 2492 matching lines @@
               node.selector, field.name, MessageKind.CANNOT_RESOLVE_SETTER);
           compiler.backend.registerThrowNoSuchMethod(mapping);
         }
         if (isComplex && getter == null && !inInstanceContext) {
           getter = warnAndCreateErroneousElement(
               node.selector, field.name, MessageKind.CANNOT_RESOLVE_GETTER);
           compiler.backend.registerThrowNoSuchMethod(mapping);
         }
       } else if (target.impliesType()) {
         compiler.backend.registerThrowNoSuchMethod(mapping);
-      } else if (target.modifiers.isFinal() || target.modifiers.isConst()) {
+      } else if (target.modifiers.isFinal() ||
+                 target.modifiers.isConst() ||
+                 (target.isFunction() &&
+                     Elements.isStaticOrTopLevelFunction(target) &&
+                     !target.isSetter())) {
         setter = warnAndCreateErroneousElement(
             node.selector, target.name, MessageKind.CANNOT_RESOLVE_SETTER);
         compiler.backend.registerThrowNoSuchMethod(mapping);
       }
     }
 
     visit(node.argumentsNode);
 
     // TODO(ngeoffray): Check if the target can be assigned.
     // TODO(ngeoffray): Warn if target is null and the send is
@@ skipping 1854 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }