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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>
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If expression
Union
def bool_instance() -> bool:
return True
reveal_type(1 if bool_instance() else 2) # revealed: Literal[1, 2]
Statically known branches
reveal_type(1 if True else 2) # revealed: Literal[1]
reveal_type(1 if "not empty" else 2) # revealed: Literal[1]
reveal_type(1 if (1,) else 2) # revealed: Literal[1]
reveal_type(1 if 1 else 2) # revealed: Literal[1]
reveal_type(1 if False else 2) # revealed: Literal[2]
reveal_type(1 if None else 2) # revealed: Literal[2]
reveal_type(1 if "" else 2) # revealed: Literal[2]
reveal_type(1 if 0 else 2) # revealed: Literal[2]
Leaked Narrowing Constraint
(issue #14588)
The test inside an if expression should not affect code outside of the expression.
def bool_instance() -> bool:
return True
x: Literal[42, "hello"] = 42 if bool_instance() else "hello"
reveal_type(x) # revealed: Literal[42] | Literal["hello"]
_ = ... if isinstance(x, str) else ...
reveal_type(x) # revealed: Literal[42] | Literal["hello"]