user/test/com/google/gwt/dev/testdata/incrementalbuildsystem/ProvidesFoo.gwt.xml

<module>
  <source path="" includes="Foo.java" />
  <generate-with class="com.google.gwt.dev.FooBarGenerator">
    <when-type-is class="com.google.gwt.dev.testdata.incrementalbuildsystem.Foo"/>
  </generate-with>
</module>