Java: Add TypeFlow base case for partially unbound types.

[aschackmull]

Base cases for TypeFlow are the places where we lose type information in a way that can affect dispatch. Stepping from an instantiated parameterised type to a fully unbound type was already covered. This PR extends this to also include the case when just 1 type argument goes from instantiated to un-instantiated.

This solves the provided example in #21066

[aschackmull]

Dca is uneventful. I also did a MRVA top 1000 check focused mainly on risk reduction to measure tuples calculated in TypeFlow - only one repo went up with more than 10% (and not much more than that), so this change seems quite safe and fairly corner-case, but certainly worth it to shore up the identified hole.

[Copilot]

Pull request overview

This PR extends TypeFlow base cases to handle transitions from instantiated to partially unbound parameterized types. Previously, only transitions to fully unbound types were covered. This enhancement addresses issue #21066 by capturing type information loss when individual type arguments become uninstantiated.

Changes:

• Added partiallyUnbound predicate to detect parameterized types with unrestricted type arguments at specific positions
• Extended the upcast predicate with a new base case for partially unbound type transitions

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[hvitved]

LGTM, but I guess it would be nice with a test case.

[aschackmull]

it would be nice with a test case.

Done!