RFR: 8343580: Type error with inner classes of generic classes in functions generic by outer

[Aggelos Biboudis]

javac determines erroneously that `getter` has a raw type (`G.Getter`). The type of `getter` is deduced as the raw type `Getters<T>.Getter` by javac. Thus, the `Object` in the following example. The question is whether it should be treated as raw or not in the scenario where the qualifying type *is* a type parameter, as in `G.Getter`. In this case `Getter` is inherited from the supertype `Getters<T>`:


static abstract class Getters<T> {
    abstract class Getter {
        abstract T get();
    }
}

static class Usage<T, G extends Getters<T>> {
    public T test(G.Getter getter) {
        return getter.get(); // incompatible types: Object cannot be converted to T
    }
}


It seems that this is a compiler bug. According to 4.8 Raw Types a “rare” type occurs when the inner is a partially raw type but the definition of Getter doesn’t take any type variables, so this is not a case of a "rare" type. `G.Getter` describes a type with a qualifying type being a type parameter which is not raw and moreover there is an instantiation of its bound. Simply not looking into the bounds of `G` seems like a compiler bug.

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Commit messages:
 - 8343580: Type error with inner classes of generic classes in functions generic by outer

Changes: https://git.openjdk.org/jdk/pull/25346/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25346&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8343580
  Stats: 48 lines in 2 files changed: 47 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25346.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25346/head:pull/25346

PR: https://git.openjdk.org/jdk/pull/25346