You'll need to put a SomeName.gwt.xml in some directory relative to
the com.gwt classpath that has <source path="demo" /> and then in
your app's entrypoint module .gwt.xml file you add a line that says
<inherits name="com.gwt.SomeName"/> where SomeName is the module you
name where you're putting your .User stuff. If you put it in
the .client sub-package relative to your entrypoint .gwt.xml you don't
have to do an inherits.