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

[Chen Liang]

On Wed, 21 May 2025 09:55:31 GMT, Aggelos Biboudis <abimpoudis at openjdk.org> wrote:

> 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.

src/jdk.compiler/share/classes/com/sun/tools/javac/code/Type.java line 1155:

> 1153:             if (allparams_field == null) {
> 1154:                 Type enclosingType = getEnclosingType();
> 1155:                 if (!enclosingType.isUnbound() && enclosingType.getUpperBound() instanceof Type t) {

Shouldn't this be a while loop in case you have G bounded by another type variable?

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PR Review Comment: https://git.openjdk.org/jdk/pull/25346#discussion_r2100448606