Extended generic type loses more specific type when using recursive type bound (works in IntelliJ)

[bennettdams]

The inferred type when using recursive type bounds is missing a more specific wildcard when looking at the definition of a variable (e.g. via hovering it). This works in IntelliJ, but not in VS Code.

VS Code:

Fruit<?>

IntelliJ:

Fruit<? extends Fruit<?>>

Environment

• Operating System: macOS Sonoma 14
• JDK version: 21.0.2
• Visual Studio Code version: 1.94.2
• Java extension version: v0.29.0

Steps To Reproduce

Here is a made-up example with two classes:

Fruit.java

public class Fruit<T extends Fruit<T>> implements Comparable<T> {
    private final Integer size;

    public Fruit(Integer size) {
        this.size = size;
    }

    public Integer getSize() {
        return size;
    }

    @Override public int compareTo(T other) {
        return size.compareTo(other.getSize());     // Now getSize() is available.
    }
}

Apple.java

class Apple extends Fruit<Apple> {
    public Apple(Integer size) {
        super(size);
    }
}

Some random class/function to check:

public Fruit<? extends Fruit<?>> getFruit(Fruit<? extends Fruit<?>> someFruit) {
    // in real world code, assume some mapper/runtime check here
    // var someFruit = ...
    return new Fruit<>(1);
}

Somewhere else:

var fruit = getFruit(new Apple(1));

Current Result

Fruit<?> (in the definition window)

Expected Result

Fruit<? extends Fruit<?>> (in the definition window)

[snjeza]

This is an upstream jdt issue. I can reproduce it in the Eclipse master branch, but I can't reproduce it in the javac branch.