[ty] Fix upcasting type[T] types to Callable types#23472
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AlexWaygood merged 5 commits intomainfrom Feb 23, 2026
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AlexWaygood
changed the title
CallableTypeOf for type and type[T] typestype and type[T] types to Callable types
Typing conformance resultsNo changes detected ✅ |
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Memory usage reportSummary
Significant changesClick to expand detailed breakdownflake8
trio
sphinx
prefect
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| Lint rule | Added | Removed | Changed |
|---|---|---|---|
invalid-argument-type |
0 | 0 | 1 |
| Total | 0 | 0 | 1 |
AlexWaygood
changed the title
type and type[T] types to Callable typestype[T] types to Callable types
AlexWaygood
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carljm,
dcreager,
ibraheemdev and
sharkdp
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AlexWaygood
changed the title
type[T] types to Callable typestype[T] types to Callable types
sharkdp
reviewed
Feb 23, 2026
| # error: [invalid-argument-type] | ||
| reveal_type(type_int([])) # revealed: int | ||
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| reveal_type(type_t_union_bound(42)) # revealed: T3@f |
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why do we reveal T3@f here for type_t_union_bound(…) (instead of TakesStrInConstructor | TakesIntInConstructor), but int for type_int()?
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calling an object of type type[int] creates an instance of int. Calling an object of type type[T3@f] creates an instance of T3@f. We cannot simplify T3@f to its upper bound here, or we lose information -- this is crucial to avoid emitting invalid-return-type diagnostics on things like this:
def f[T3: int](x: type[T3]) -> T3:
return x()I considered adding a test, but IIRC I think we have good test coverage for this pattern elsewhere
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oh 🙈. I was reading those tests wrong. I saw type_t_int_bound: type[T2], and thought we were calling it to get int. But there's also an actual type[int] parameter there. And type_t_int_bound isn't even tested.
Now it makes more sense! I was indeed more worried about the int answer compared to the T3@f answer.
carljm
reviewed
Feb 23, 2026
| type_t_unbound: type[T], | ||
| type_t_object_bound: type[T1], | ||
| type_int: type[int], | ||
| type_t_int_bound: type[T2], |
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This doesn't seem to be used in the tests? (I think @sharkdp pointed this out below also)
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Summary
Currently we do not emit an error on this -- but other type checkers do, and we should too:
This PR fixes that, and some related bugs. I traced back some unexpected ecosystem changes in #23428 as being ultimately caused by these underlying bugs.
There are still some TODOs in the mdtests added here. I know exactly how to fix them, but fixing them is more disruptive than any of the changes being applied here -- so I'm holding off on applying those fixes for now. It's best to consider them separately, I think.
Test Plan
Mdtests