When APT compiles a source code that refers to a non-existent annotation, such as:

  @NoSuchAnnotation
  class A {}

APT correctly reports an error:

  Test.java:1: cannot find symbol
  symbol : class NoSuchAnnotation
  location: class A
        @NoSuchAnnotation
         ^
but then it nevertheless lets annotation processors a chance to introspect this class A.
When our annotation processor does:

        for( AnnotationMirror m : decl.getAnnotationMirrors() ) {
             AnnotationType at = m.getAnnotationType();
             ...
        }

It causes a ClassCastException as follows:

    java.lang.ClassCastException: com.sun.tools.apt.mirror.type.ClassTypeImpl
        at com.sun.tools.apt.mirror.declaration.AnnotationMirrorImpl.getAnnotationType(AnnotationMirrorImpl.java:82)

which is at the following line:

    public AnnotationType getAnnotationType() {
        return (AnnotationType) env.typeMaker.getType(anno.type);
    }

... presumably because typeMaker returns a token that designates an error, which doesn't implement AnnotationType.

A few observations:

1. if a special TypeMirror that represents an error is used (which is a common technique so that the caller can avoid constantly checking against error conditions), then it should implement all TypeMirror subtypes, so that it can be used everywhere.

2. Alternatively, return null from the getAnnotationType(). In a few other parts of the APT API, null is returned for errors, so that seems to be in alignment with the rest. I find it unfortunate that I have to check null all the time in so many places, which makes my annotation processor looks like some C program.

3. For the purpose of my annotation processor, it's acceptable not to process anything at all and abort right away if there's any compilation error in the source code. It would be great if AnnotationProcessorEnvironment can make that information available to me.