New "keyfor" errors with getClass() with 3.16.0 and beyond

[Kenneth Knowles]

Hello,

TL;DR: It seems that most or all uses of getClass() produce [super @KeyForBottom Void] and the uses in the code expect [super @UnknownKeyFor NullType] starting with checkerframework 3.16.0. Is there some specific change in 3.16.0 that introduces this that I can learn about? Does anyone know how to work around it?

Details:

I am trying to upgrade the checkerframework version used by Apache Beam. When I reach 3.16.0 I hit a new issue I do not yet understand how to fix. The issue persists through 3.27.0. There are checker framework crashes in 3.16.0 and 3.17.0 that are not relevant, so I will submit my question with 3.18.0.

• The pull request: https://github.com/apache/beam/pull/24406
• The build output: https://ci-beam.apache.org/job/beam_PreCommit_Spotless_Commit/23928/console

It seems most of the errors are roughly similar. Here is one (note that the method name is "TypeDescriptors.of" so it reads a little funny):

    TypeDescriptors.java:354: error: [type.argument] incompatible type argument for type parameter T extends Object of of.
             (TypeDescriptor<T>) TypeDescriptor.of(instance.getClass()), supertype, extractor);
                                              ^
      found   : capture#464[ extends @UnknownKeyFor Object super @KeyForBottom Void]
      required: [extends @UnknownKeyFor Object super @UnknownKeyFor NullType]

The code in question:

    public static <T, V> TypeDescriptor<V> extractFromTypeParameters(
        @NonNull T instance, Class<? super T> supertype, TypeVariableExtractor<T, V> extractor) {
      return extractFromTypeParameters(
          (TypeDescriptor<T>) TypeDescriptor.of(instance.getClass()), supertype, extractor);
    }

There are quite a few other similar, typically simple, uses.

Kenn