[ty] Fix false positive for bounded type parameters with NewType#22542
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[ty] Fix false positive for bounded type parameters with NewType#22542
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…king When calling a method on an instance of a generic class with bounded type parameters (e.g., `C[T: K]` where `K` is a NewType), ty was incorrectly reporting: "Argument type `C[K]` does not satisfy upper bound `C[T@C]` of type variable `Self`" The issue was introduced by PR #22105, which moved the catch-all case for NewType assignments that falls back to the concrete base type. This case was placed before the TypeVar handling cases, so when checking `K <: T@C` (where K is a NewType and T@C is a TypeVar with upper bound K): 1. The NewType fallback matched first 2. It delegated to `int` (K's concrete base type) 3. Then checked `int <: T@C`, which checks if `int` satisfies bound `K` 4. But `int` is not assignable to `K` (NewTypes are distinct from their bases) The fix moves the NewType fallback case after the TypeVar cases, so TypeVar handling takes precedence. Fixes astral-sh/ty#2467
Diagnostic diff on typing conformance testsNo changes detected when running ty on typing conformance tests ✅ |
|
carljm
requested review from
AlexWaygood,
dcreager and
sharkdp
as code owners
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Fixes astral-sh/ty#2467
When calling a method on an instance of a generic class with bounded type parameters (e.g.,
C[T: K]whereKis a NewType), ty was incorrectly reporting: "Argument typeC[K]does not satisfy upper boundC[T@C]of type variableSelf"The issue was introduced by PR #22105, which moved the catch-all case for NewType assignments that falls back to the concrete base type. This case was moved before the TypeVar handling cases, so when checking
K <: T@C(where K is a NewType and T@C is a TypeVar with upper bound K):int(K's concrete base type)int <: T@C, which checks ifintsatisfies boundKintis not assignable toK(NewTypes are distinct from their bases)The fix moves the NewType fallback case after the TypeVar cases, so TypeVar handling takes precedence. Now when checking
K <: T@C, we use the TypeVar case at line 828 which returnsfalsefor non-inferable typevars - but this is correct because the other direction (T@C <: K) passes, and for the overall specialization comparison both directions are checked.