[ty] Fix subtyping/assignability of function- and class-literal types to callback protocols#20363
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AlexWaygood merged 2 commits intomainfrom Sep 12, 2025
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Diagnostic diff on typing conformance testsChanges were detected when running ty on typing conformance tests--- old-output.txt 2025-09-12 12:44:28.523759463 +0000
+++ new-output.txt 2025-09-12 12:44:31.537763957 +0000
@@ -112,9 +112,23 @@
callables_kwargs.py:62:5: error[missing-argument] No argument provided for required parameter `v3` of function `func2`
callables_kwargs.py:64:11: error[invalid-argument-type] Argument to function `func2` is incorrect: Expected `str`, found `Literal[1]`
callables_kwargs.py:65:5: error[missing-argument] No argument provided for required parameter `v3` of function `func2`
+callables_kwargs.py:103:1: error[invalid-assignment] Object of type `def func1(**kwargs: @Todo(`Unpack[]` special form)) -> None` is not assignable to `TDProtocol5`
+callables_kwargs.py:134:1: error[invalid-assignment] Object of type `def func7(*, v1: int, v3: str, v2: str = Literal[""]) -> None` is not assignable to `TDProtocol6`
+callables_protocol.py:35:1: error[invalid-assignment] Object of type `def cb1_bad1(*vals: bytes, *, max_items: int | None) -> list[bytes]` is not assignable to `Proto1`
+callables_protocol.py:36:1: error[invalid-assignment] Object of type `def cb1_bad2(*vals: bytes) -> list[bytes]` is not assignable to `Proto1`
+callables_protocol.py:37:1: error[invalid-assignment] Object of type `def cb1_bad3(*vals: bytes, *, max_len: str | None) -> list[bytes]` is not assignable to `Proto1`
+callables_protocol.py:67:1: error[invalid-assignment] Object of type `def cb2_bad1(*a: bytes) -> Unknown` is not assignable to `Proto2`
+callables_protocol.py:68:1: error[invalid-assignment] Object of type `def cb2_bad2(*a: str, **b: str) -> Unknown` is not assignable to `Proto2`
+callables_protocol.py:69:1: error[invalid-assignment] Object of type `def cb2_bad3(*a: bytes, **b: bytes) -> Unknown` is not assignable to `Proto2`
+callables_protocol.py:70:1: error[invalid-assignment] Object of type `def cb2_bad4(**b: str) -> Unknown` is not assignable to `Proto2`
callables_protocol.py:97:1: error[invalid-assignment] Object of type `def cb4_bad1(x: int) -> None` is not assignable to `Proto4`
callables_protocol.py:121:1: error[invalid-assignment] Object of type `def cb6_bad1(*vals: bytes, *, max_len: int | None = None) -> list[bytes]` is not assignable to `NotProto6`
+callables_protocol.py:169:1: error[invalid-assignment] Object of type `def cb8_bad1(x: int) -> Any` is not assignable to `Proto8`
callables_protocol.py:179:62: error[invalid-return-type] Function always implicitly returns `None`, which is not assignable to return type `R@__call__`
+callables_protocol.py:238:1: error[invalid-assignment] Object of type `def cb11_bad1(x: int, y: str, /) -> Any` is not assignable to `Proto11`
+callables_protocol.py:260:1: error[invalid-assignment] Object of type `def cb12_bad1(*args: Any, *, kwarg0: Any) -> None` is not assignable to `Proto12`
+callables_protocol.py:284:1: error[invalid-assignment] Object of type `def cb13_no_default(path: str) -> str` is not assignable to `Proto13_Default`
+callables_protocol.py:311:1: error[invalid-assignment] Object of type `def cb14_no_default(*, path: str) -> str` is not assignable to `Proto14_Default`
callables_subtyping.py:26:5: error[invalid-assignment] Object of type `(int, /) -> int` is not assignable to `(int | float, /) -> int | float`
callables_subtyping.py:29:5: error[invalid-assignment] Object of type `(int | float, /) -> int | float` is not assignable to `(int, /) -> int`
classes_classvar.py:38:11: error[invalid-type-form] Type qualifier `typing.ClassVar` expected exactly 1 argument, got 2
@@ -675,6 +689,7 @@
narrowing_typeis.py:92:9: error[type-assertion-failure] Argument does not have asserted type `B`
narrowing_typeis.py:96:9: error[type-assertion-failure] Argument does not have asserted type `B`
narrowing_typeis.py:132:20: error[invalid-argument-type] Argument to function `takes_callable_str` is incorrect: Expected `(object, /) -> str`, found `def simple_typeguard(val: object) -> TypeIs[int]`
+narrowing_typeis.py:152:26: error[invalid-argument-type] Argument to function `takes_callable_str_proto` is incorrect: Expected `CallableStrProto`, found `def simple_typeguard(val: object) -> TypeIs[int]`
narrowing_typeis.py:191:18: error[invalid-argument-type] Argument to function `takes_int_typeis` is incorrect: Expected `(object, /) -> TypeIs[int]`, found `def bool_typeis(val: object) -> TypeIs[bool]`
overloads_basic.py:39:1: error[invalid-argument-type] Method `__getitem__` of type `Overload[(__i: int, /) -> int, (__s: slice[Any, Any, Any], /) -> bytes]` cannot be called with key of type `Literal[""]` on object of type `Bytes`
overloads_definitions.py:20:5: error[invalid-overload] Overloaded function `func1` requires at least two overloads
@@ -854,5 +869,5 @@
typeddicts_usage.py:28:1: error[missing-typed-dict-key] Missing required key 'name' in TypedDict `Movie` constructor
typeddicts_usage.py:28:18: error[invalid-key] Invalid key access on TypedDict `Movie`: Unknown key "title"
typeddicts_usage.py:40:24: error[invalid-type-form] The special form `typing.TypedDict` is not allowed in type expressions. Did you mean to use a concrete TypedDict or `collections.abc.Mapping[str, object]` instead?
-Found 855 diagnostics
+Found 870 diagnostics
WARN A fatal error occurred while checking some files. Not all project files were analyzed. See the diagnostics list above for details. |
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The conformance suite diff looks excellent -- the new diagnostics are all on lines that have |
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AlexWaygood
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Mypy_primer analysispsycopgpsycopg (https://github.com/psycopg/psycopg)
+ tests/typing_example.py:100:21: error[invalid-argument-type] Argument to bound method `connect` is incorrect: Expected `RowFactory[tuple[Any, ...]] | None`, found `def int_row_factory(cursor: Cursor[Any] | AsyncCursor[Any]) -> (Sequence[int], /) -> int`
+ tests/typing_example.py:110:21: error[invalid-argument-type] Argument to bound method `connect` is incorrect: Expected `RowFactory[tuple[Any, ...]] | None`, found `bound method <class 'Person'>.row_factory(cursor: Cursor[Any] | AsyncCursor[Any]) -> (Sequence[str], /) -> Person`
+ tests/typing_example.py:134:43: error[invalid-argument-type] Argument to bound method `connect` is incorrect: Expected `AsyncRowFactory[tuple[Any, ...]] | None`, found `def int_row_factory(cursor: Cursor[Any] | AsyncCursor[Any]) -> (Sequence[int], /) -> int`
+ tests/typing_example.py:144:43: error[invalid-argument-type] Argument to bound method `connect` is incorrect: Expected `AsyncRowFactory[tuple[Any, ...]] | None`, found `bound method <class 'Person'>.row_factory(cursor: Cursor[Any] | AsyncCursor[Any]) -> (Sequence[str], /) -> Person`This is pretty interesting. Here's a minimal repro of what's going on here: from __future__ import annotations
from typing import Protocol, Any
def int_maker() -> int:
raise NotImplementedError
class RowMaker[Row = tuple[Any, ...]](Protocol):
def __call__(self) -> Row: ...
class Connection[Row = tuple[Any, ...]]:
@classmethod
def connect(cls, factory: RowMaker[Row]) -> Row:
raise NotImplementedError
connect = Connection.connect
reveal_type(connect(int_maker))Mypy issues no complaints on this code and reveals And with this PR, ty would match pyright's behaviour. The difference comes down to what the inferred type of Anyway, I think the fact that we are emulating pyright's behaviour here means that this is pretty defensible behaviour from us! werkzeugwerkzeug (https://github.com/pallets/werkzeug)
+ tests/test_formparser.py:437:45: error[invalid-argument-type] Argument to bound method `__init__` is incorrect: Expected `TStreamFactory | None`, found `def stream_factory() -> Unknown`This seems like a clear true positive. Not sure I have the energy on a Friday evening to trawl through the pandas codebase figuring out what the new diagnostics there are about... |
AlexWaygood
requested review from
carljm,
dcreager and
sharkdp
as code owners
carljm
approved these changes
Sep 12, 2025
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Summary
Fixes astral-sh/ty#377.
We were treating any function as being assignable to any callback protocol, because we were trying to figure out a type's
Callablesupertype by looking up the__call__attribute on the type's meta-type. But a function-literal's meta-type istypes.FunctionType, andtypes.FunctionType.__call__is(...) -> Any, which is not very helpful!While working on this PR, I also realised that assignability between class-literals and callback protocols was somewhat broken too, so I fixed that at the same time.
Test Plan
Added mdtests