Missing TypeIs narrowing for variadic tuples #17599
Description
I noticed this behavior when investigating a similar issue in pyright.
Mypy isn't correctly narrowing tuples in some cases.
from typing_extensions import TypeIs
def is_tuple_of_strings(v: tuple[int | str, ...]) -> TypeIs[tuple[str, ...]]:
return all(isinstance(x, str) for x in v)
def test1(t: tuple[int]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be Never ✅
else:
reveal_type(t) # Should be tuple[int] ✅
def test2(t: tuple[str, int]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be Never ✅
else:
reveal_type(t) # Should be tuple[str, int] ✅
def test3(t: tuple[int | str]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be tuple[str] ✅
else:
reveal_type(t) # Should be tuple[int] or tuple[int | str] ❌ (mypy: Never)
def test4(t: tuple[int | str, int | str]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be tuple[str, str] ✅
else:
reveal_type(t) # Should be tuple[int | str, int | str] or tuple[int, int | str] | tuple[str, int] ❌ (mypy: Never)
def test5(t: tuple[int | str, ...]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be tuple[str, ...] ✅
else:
reveal_type(t) # Should be tuple[int | str, ...] ❌ (mypy: Never)
def test6(t: tuple[str, *tuple[int | str, ...], str]) -> None:
if is_tuple_of_strings(t):
reveal_type(t) # Should be tuple[str, *tuple[str, ...], str] ❌ (mypy: tuple[str, Never, str])
else:
reveal_type(t) # Should be tuple[str, *tuple[int | str, ...], str] ❌ (mypy: Never)