Incorrect join result in the presence of Any #11925
Description
Given test.py:
from unknown import X
class A: ...
class B(X, A): ...
class C(B): ...
class D(C): ...
class E(D): ...
reveal_type(E() if bool() else D())
Running mypy test.py --ignore-missing-imports gives test.py:10: note: Revealed type is "x.A"
Stepping through, things get unexpected starting here:
Line 75 in 1beed9a
That is, mypy thinks D is a subtype of E!!! This seems obviously False; E is a subtype of D.
It turns out that due to the unknown type, TypeInfo(D).fallback_to_any is True, and so we throw our hands in the air and return True.
Line 243 in 1beed9a
The following diff fixes this case, but needs to be investigated further:
diff --git a/mypy/join.py b/mypy/join.py
index d298b495f..392c79a07 100644
--- a/mypy/join.py
+++ b/mypy/join.py
@@ -72,7 +72,9 @@ class InstanceJoiner:
assert new_type is not None
args.append(new_type)
result: ProperType = Instance(t.type, args)
- elif t.type.bases and is_subtype(t, s, ignore_type_params=True):
+ elif t.type.bases and is_subtype(t, s, ignore_type_params=True) and not (
+ isinstance(t, Instance) and t.type.fallback_to_any
+ ):
result = self.join_instances_via_supertype(t, s)
else:
# Now t is not a subtype of s, and t != s. Now s could be a subtype