Make aggregating annotation processors faster Aggregating processors need to reprocess all classes they are interested in on any change. Until now this was ensured by passing all their source files to the compiler for recompilation.
However, the Java compiler can run annotation processing on class files too. So instead of recompiling the (unchanged) source files we now tell the compiler which classes to reprocess. This adds a small new limitation for aggregating processors - their annotations need to have at least CLASS retention to be visible in the class files. The benefit is much faster compilation.