How to access type annotations on a receiver type's parameters

Question

I am looking at a rather trivial class with a single method that defines an annotated receiver type:

class Foo<T> { 
  void foo(Foo<@Bar T> this) {}
}

I would now like to access the type annotation on the receiver type's parameter @Bar but the Java reflection API returns an annotated raw type when accessing the receiver:

assert Foo.class.getDeclaredMethod("foo")
                .getAnnotatedReceiverType() 
  instanceof AnnotatedParameterizedType;

The assertion fails as the annotated type that is returned is returned as a raw type Foo. Is this intentional? I can still find the @Bar annotation when accessing private properties of the implementation of AnnotatedType that is returned.

I am running a recent version of Java 8.

Answer 1

This is a known bug JDK-8058220. However, the problem is deeper that it may seem.

It cannot be easily fixed without changes to class file format and corresponding specification updates. Currently the class file does not contain information required to distinguish receiver parameter from a regular one (see JDK-8062582).

Answer 2

Turns out this is a simple bug. I first thought, this is an implicitation of the linked issues but type annotations have nothing to do with that. Type annotations are poorly tested in the current implementation of the Java runtime. I found a sheer number of issues when deep diving into the matter:

• A receiver type is not resolved as a parameterized type.
• Type annotations on parameters of multiple type variable bound types are not filtered to their respective bound.
• Impossible to read owner type of an annotated parameterized type.
• Example of wrong type annotation indexing of type varaible bounds on recursive type variables by Java Core reflection.