https://code.google.com/p/dart/issues/detail?id=223

compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java

Index: compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java
===================================================================
--- compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java	(revision 1034)
+++ compiler/java/com/google/dart/compiler/resolver/MemberBuilder.java	(working copy)
@@ -113,6 +113,7 @@
           case NONE:
           case CONSTRUCTOR:
             element = buildConstructor(method);
+            checkConstructor(element, method);
             addConstructor((ClassElement) currentHolder, (ConstructorElement) element);
             break;
 
@@ -429,6 +430,13 @@
       // example const and missing body.
     }
 
+    private void checkConstructor(MethodElement element, DartMethodDefinition method) {
+      if (Elements.isNonFactoryConstructor(element) && method.getFunction() != null
+          && method.getFunction().getReturnTypeNode() != null) {
+        resolutionError(method, ResolverErrorCode.CONSTRUCTOR_CANNOT_HAVE_RETURN_TYPE);
+      }
+    }
+
     private void checkUniqueName(EnclosingElement holder, Element e) {
       Element other = lookupElementByName(holder, e.getName(), e.getModifiers());
       assert e != other : "forgot to call checkUniqueName() before adding to the class?";