Reference implementation scope

[jspecify]

Reference implementation scope

[wmdietlGC]

I don't think the RI should provide extensions to the Java language model, implement ways to query for a type, etc.

Two things can be enforced:

• All annotations are used in meaningful ways, e.g. forbid @Nullable @NotNull and any annotation on primitives. Enforce TYPE_USE restrictions listed in Issue #17. TODO: produce full list of these consistency checks.
• Behavioral subtyping, that is, annotations on an override are consistent with the super method.

In particular, we should refrain from prescribing when nullness errors should be raised in expressions. Different static analysis tools will provide additional refinement, e.g. pre-condition annotations, that refine a field that is declared nullable to be not-null.
We should also not guarantee that all dereferences of something @NotNull will be allowed - e.g. the Checker Framework provides fine-grained initialization checking that makes sure uninitialized fields aren't used. This will result in errors for uses of a not-null field.

[kevinb9n]

Narrow works for us.

[kevinb9n]

By #92 there won't be an RI.