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types overlap only if all type args match #9452

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Merged
merged 1 commit into from
Sep 18, 2020
Merged

types overlap only if all type args match #9452

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6 changes: 3 additions & 3 deletions mypy/meet.py
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Original file line number Diff line number Diff line change
Expand Up @@ -339,9 +339,9 @@ def _type_object_overlap(left: Type, right: Type) -> bool:
# Or, to use a more concrete example, List[Union[A, B]] and List[Union[B, C]]
# would be considered partially overlapping since it's possible for both lists
# to contain only instances of B at runtime.
Comment on lines 339 to 341
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Looking at this example I am wondering if the original behavior wasn't intentional?

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The example only has a single type argument; I think the case with multiple args was just not considered.

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I stumbled a little on this too, unions are dealt with by the recursive call, about a hundred lines earlier in the function

for left_arg, right_arg in zip(left.args, right.args):
if _is_overlapping_types(left_arg, right_arg):
return True
if all(_is_overlapping_types(left_arg, right_arg)
for left_arg, right_arg in zip(left.args, right.args)):
return True

return False

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22 changes: 22 additions & 0 deletions test-data/unit/check-overloading.test
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Expand Up @@ -5151,3 +5151,25 @@ compose(ID, fakeint)("test")
reveal_type(compose(ID, fakeint)) # N: Revealed type is 'def (Union[builtins.str, builtins.bytes]) -> __main__.ID*'

[builtins fixtures/tuple.pyi]

[case testOverloadTwoTypeArgs]
from typing import Generic, overload, TypeVar, Any

T1 = TypeVar("T1")
T2 = TypeVar("T2")

class A: ...
class B: ...
class G(Generic[T1, T2]): ...

@overload
def f1(g: G[A, A]) -> A: ...
@overload
def f1(g: G[A, B]) -> B: ...
def f1(g: Any) -> Any: ...

@overload
def f2(g: G[A, Any]) -> A: ... # E: Overloaded function signatures 1 and 2 overlap with incompatible return types
@overload
def f2(g: G[A, B], x: int = ...) -> B: ...
def f2(g: Any, x: int = ...) -> Any: ...