Create a new class in the 'client' package of a GWT project:
public class BadClass extends JPanel
Then do a build. The error is noted, but there is no information
about which file/line contains the error. For a large project this
can become unmanageable very quickly as one must resort
to guesswork to locate the build errors.
The above is but one example, but the general rule holds: No
file/line info is presented with GWT build errors.