Via the -lib argument and the -listener argument, we can inject some code that understands what Ant is doing. We can learn which task in which target has failed and report it in the UI, we can learn the <javac> invocation to figure out where the source tree is, we can detect <junit> invocation to auto-record unit tests, etc.

This can also then be used for other kinds of build comprehension, such as Gradle, which uses Ant internally.