[ty] Support solving generics involving PEP 695 type aliases#22678
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ibraheemdev merged 1 commit intoastral-sh:mainfrom Jan 21, 2026
Merged
[ty] Support solving generics involving PEP 695 type aliases#22678ibraheemdev merged 1 commit intoastral-sh:mainfrom
ibraheemdev merged 1 commit intoastral-sh:mainfrom
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bxff
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AlexWaygood,
carljm,
dcreager and
sharkdp
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Typing conformance resultsNo changes detected ✅ |
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-await |
0 | 0 | 6 |
invalid-return-type |
1 | 4 | 1 |
invalid-argument-type |
1 | 2 | 0 |
unused-ignore-comment |
2 | 0 | 0 |
| Total | 4 | 6 | 7 |
AlexWaygood
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ibraheemdev
reviewed
Jan 21, 2026
ibraheemdev
reviewed
Jan 21, 2026
| reveal_type(head(["a", "b"])) # revealed: str | ||
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| d: dict[str, int] = {"a": 1} | ||
| reveal_type(get_value(d, "a")) # revealed: int |
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Can we also add tests for the reverse direction, e.g.,
type MyList[T] = list[T]
def head[T](list: list[T]) -> T:
return list[0]
def _(x: MyList[int]):
reveal_type(head(x)) # revealed: intThis test fails on main.
Member
|
Interestingly there seems to be no ecosystem impact (I believe most of the changes are spurious), but this should be good to land after the added test. A rebase should also fix the failing benchmark job. |
Add support for type variable inference when a PEP 695 type alias is used as a function parameter or argument type. Changes: - Formal type alias expansion: Add match arm to expand formal type aliases so their underlying structure (e.g., list[T]) is visible for matching - Actual type alias expansion: Add match arm at the end to expand actual type aliases while preserving alias identity for direct TypeVar matches Test Plan: - Add tests for solving generics with type alias parameters - Add test for reverse direction (type alias as argument type) Closes astral-sh/ty#1851
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Thanks! |
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Summary
Fixes type variable inference when a PEP 695 type alias is used as a function parameter.
Before:
After: Correctly infers
intby expandingMyList[T]tolist[T]during solving.Changes in
generics.rs:reveal_type()and literal promotionListOfPairs[T] = list[Pair[T]]The early/late expansion asymmetry is intentional: formal needs structural visibility; actual needs identity preservation.
Test Plan
aliases.mdcovering simple, nested, and union alias casesCloses astral-sh/ty#1851