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Fix tuple subtyping #16073

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Fix tuple subtyping #16073

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e5b617c
Fix tuple subtyping
hauntsaninja Sep 9, 2023
f4fa3d6
regression test
hauntsaninja Sep 9, 2023
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2 changes: 1 addition & 1 deletion mypy/main.py
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Original file line number Diff line number Diff line change
Expand Up @@ -1359,7 +1359,7 @@ def set_strict_flags() -> None:
parser.error("Can only find occurrences of class members.")
if len(_find_occurrences) != 2:
parser.error("Can only find occurrences of non-nested class members.")
state.find_occurrences = _find_occurrences # type: ignore[assignment]
state.find_occurrences = _find_occurrences

# Set reports.
for flag, val in vars(special_opts).items():
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6 changes: 4 additions & 2 deletions mypy/subtypes.py
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Expand Up @@ -435,8 +435,10 @@ def visit_instance(self, left: Instance) -> bool:
# dynamic base classes correctly, see #5456.
return not isinstance(self.right, NoneType)
right = self.right
if isinstance(right, TupleType) and right.partial_fallback.type.is_enum:
return self._is_subtype(left, mypy.typeops.tuple_fallback(right))
if isinstance(right, TupleType):
return self._is_subtype(left, right.partial_fallback) and self._is_subtype(
left, mypy.typeops.tuple_fallback(right)
)
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Sorry, but this is wrong. IIUC this will make tuple[object, ...] a subtype of tuple[int, str]. While even tuple[int, ...] shoul not be a subtype of tuple[int, int]. Really only tuple[Any, ...] should be a subtype of say tuple[int, int]. This is the same as we consider *args: Any in callables very differently from *args: object or *args: int.

Note btw this question will appear even broader in context of my upcoming PR for variadic types, e.g. should we also special case Foo[int, *tuple[Any, ...], str] similarly in spirit to extending the special-casing of trivial arguments to trivial suffix in #15913. (Btw I would say yes, but it should be a separate PR after we gain more experience).

Also I bet most of the unused type ignores in mypy primer are from situations like:

v: tuple[int, ...]
if len(v) == 2:
    x: tuple[int, int] = v

(as e.g. for ignore in mypy itself). See also #1178. The proper way to solve such issues is by finally completing #10367. Unfortunately author is not responding anymore, so one of us may need to complete the PR, since it is an important one.

if isinstance(right, Instance):
if type_state.is_cached_subtype_check(self._subtype_kind, left, right):
return True
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18 changes: 17 additions & 1 deletion test-data/unit/check-tuples.test
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Expand Up @@ -113,7 +113,7 @@ t1: Tuple[A, A]
t2: tuple

if int():
t1 = t2 # E: Incompatible types in assignment (expression has type "Tuple[Any, ...]", variable has type "Tuple[A, A]")
t1 = t2
if int():
t2 = t1

Expand Down Expand Up @@ -1522,3 +1522,19 @@ class Bar(aaaaaaaaaa): # E: Name "aaaaaaaaaa" is not defined
class FooBarTuple(Tuple[Foo, Bar]):
...
[builtins fixtures/tuple.pyi]

[case testTupleOverloadZipAny]
from typing import Any, Iterable, Iterator, Tuple, TypeVar, overload

T = TypeVar("T")

@overload
def zip(__i: Iterable[T]) -> Iterator[Tuple[T]]: ...
@overload
def zip(*i: Iterable[Any]) -> Iterator[Tuple[Any, ...]]: ...
def zip(i): ...

def g(t: Tuple):
reveal_type(zip(*t)) # N: Revealed type is "typing.Iterator[builtins.tuple[Any, ...]]"
reveal_type(zip(t)) # N: Revealed type is "typing.Iterator[Tuple[Any]]"
[builtins fixtures/tuple.pyi]
4 changes: 1 addition & 3 deletions test-data/unit/check-typevar-tuple.test
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Expand Up @@ -60,9 +60,7 @@ reveal_type(f(f_args3)) # N: Revealed type is "Tuple[builtins.str, builtins.str
f(empty) # E: Argument 1 to "f" has incompatible type "Tuple[()]"; expected "Tuple[int]"
f(bad_args) # E: Argument 1 to "f" has incompatible type "Tuple[str, str]"; expected "Tuple[int, str]"

# The reason for error in subtle: actual can be empty, formal cannot.
reveal_type(f(var_len_tuple)) # N: Revealed type is "Tuple[builtins.str, Unpack[builtins.tuple[builtins.int, ...]]]" \
# E: Argument 1 to "f" has incompatible type "Tuple[int, ...]"; expected "Tuple[int, Unpack[Tuple[int, ...]]]"
reveal_type(f(var_len_tuple)) # N: Revealed type is "Tuple[builtins.str, Unpack[builtins.tuple[builtins.int, ...]]]"
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The error is correct, because () is an element of tuple[int, ...] but it is not an element of tuple[int, *tuple[int, ...]] (this must have at least one integer in the tuple). So tuple[int, ...] is not a subtype of tuple[int, *tuple[int, ...]]


g_args: Tuple[str, int]
reveal_type(g(g_args)) # N: Revealed type is "Tuple[builtins.str, builtins.str]"
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