fun foo(a: ClassA) {
    val b: ClassA.ClassB = with(a) {
        object : ClassA.ClassB() {

        }
    }
    println(b)
}

Given the above code, IDEA does not complain, but the compiler throws an internal error when trying to compile it. This may be a bug...

okkero:

ClassA.ClassB()

is not possible at all. you need an instance of

ClassA

to create a

ClassB

Yes. Hence the

with(a)

. In the lambda following it the receiver is an instance of

ClassA

. This should not be a problem.

so where does

object: ClassA.ClassB()

get the instance from? implicitly?

Yes. I would expect so. But the point is that the compiler throws an internal error trying to compile it

yeah, if IDEA doesnt complain and the compiler produces an exception, you should report it