In apt/main/Main.java, there are a couple of places where all errors
and exceptions are caught and dealt with, along the lines of:

} catch (OutOfMemoryError ex) {
resourceMessage(ex);
return EXIT_SYSERR;
} catch (StackOverflowError ex) {
resourceMessage(ex);
return EXIT_SYSERR;
} catch (FatalError ex) {
feMessage(ex);
return EXIT_SYSERR;
} catch (Throwable ex) {
bugMessage(ex);
return EXIT_ABNORMAL;
} finally {

We need to sanity-check each of these possibilities, to make sure it's
doing something appropriate. One problem I noticed is if an annotation
processor throws an error (perhaps an assertion failure), the tool writes
this inappropriate message to stderr:

An exception has occurred in the compiler (1.5.0-internal). Please
file a bug at the Java Developer Connection
(http://java.sun.com/cgi-bin/bugreport.cgi) after checking the Bug
Parade for duplicates. Include your program and the following
diagnostic in your report. Thank you.

This particular message comes from the bugMessage method, but there are
a number of similar methods that should be checked too.