Better error message for ui:attribute

Review at http://gwt-code-reviews.appspot.com/1454809

Review by: rchandia@google.com

git-svn-id: https://google-web-toolkit.googlecode.com/svn/trunk@10308 8db76d5a-ed1c-0410-87a9-c151d255dfc7

user/src/com/google/gwt/uibinder/rebind/messages/MessagesWriter.java

diff --git a/user/src/com/google/gwt/uibinder/rebind/messages/MessagesWriter.java b/user/src/com/google/gwt/uibinder/rebind/messages/MessagesWriter.java
index 61f0b00..915f85c 100644
--- a/user/src/com/google/gwt/uibinder/rebind/messages/MessagesWriter.java
+++ b/user/src/com/google/gwt/uibinder/rebind/messages/MessagesWriter.java
@@ -121,7 +121,8 @@
         logger.die(child, "Missing name attribute");
       }
       if (!elem.hasAttribute(attributeName)) {
-        logger.die(child, "Enclosing element has no matching attribute");
+        logger.die(child, "The enclosing element needs to provide a "
+            + "default value for attribute \"%s\"", attributeName);
       }
       XMLAttribute attribute = elem.getAttribute(attributeName);
       if (attribute.hasComputedValue()) {