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557d583e32
Fix #14558 ## Summary - Add `typing.NoReturn` and `typing.Never` to known instances and infer them as `Type::Never` - Add `is_assignable_to` cases for `Type::Never` I skipped emitting diagnostic for when a function is annotated as `NoReturn` but it actually returns. ## Test Plan Added tests from https://github.com/python/typing/blob/main/conformance/tests/specialtypes_never.py except from generics and checking if the return value of the function and the annotations match. --------- Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com> Co-authored-by: Carl Meyer <carl@astral.sh>
1.2 KiB
1.2 KiB
NoReturn & Never
NoReturn is used to annotate the return type for functions that never return. Never is the
bottom type, representing the empty set of Python objects. These two annotations can be used
interchangeably.
Function Return Type Annotation
from typing import NoReturn
def stop() -> NoReturn:
raise RuntimeError("no way")
# revealed: Never
reveal_type(stop())
Assignment
from typing import NoReturn, Never, Any
# error: [invalid-type-parameter] "Type `typing.Never` expected no type parameter"
x: Never[int]
a1: NoReturn
# TODO: Test `Never` is only available in python >= 3.11
a2: Never
b1: Any
b2: int
def f():
# revealed: Never
reveal_type(a1)
# revealed: Never
reveal_type(a2)
# Never is assignable to all types.
v1: int = a1
v2: str = a1
# Other types are not assignable to Never except for Never (and Any).
v3: Never = b1
v4: Never = a2
v5: Any = b2
# error: [invalid-assignment] "Object of type `Literal[1]` is not assignable to `Never`"
v6: Never = 1
Typing Extensions
from typing_extensions import NoReturn, Never
x: NoReturn
y: Never
def f():
# revealed: Never
reveal_type(x)
# revealed: Never
reveal_type(y)