From c44bebbf1594fa19c9e66070b51355d6ee59b24c Mon Sep 17 00:00:00 2001
From: hauntsaninja <hauntsaninja@gmail.com>
Date: Thu, 5 Jan 2023 21:25:13 -0800
Subject: [PATCH] Fix incorrect join in the presence of Any fallback

Fixes #11925
---
 mypy/join.py                        |  5 ++++-
 mypy/subtypes.py                    |  6 +-----
 test-data/unit/check-inference.test | 12 ++++++++++++
 3 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/mypy/join.py b/mypy/join.py
index 84aa03f8eeba..62d256f4440f 100644
--- a/mypy/join.py
+++ b/mypy/join.py
@@ -9,6 +9,7 @@
 from mypy.nodes import CONTRAVARIANT, COVARIANT, INVARIANT
 from mypy.state import state
 from mypy.subtypes import (
+    SubtypeContext,
     find_member,
     is_equivalent,
     is_proper_subtype,
@@ -101,7 +102,9 @@ def join_instances(self, t: Instance, s: Instance) -> ProperType:
                 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_proper_subtype(
+            t, s, subtype_context=SubtypeContext(ignore_type_params=True)
+        ):
             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
diff --git a/mypy/subtypes.py b/mypy/subtypes.py
index 61ba7af5147f..d76b45779a6d 100644
--- a/mypy/subtypes.py
+++ b/mypy/subtypes.py
@@ -103,11 +103,7 @@ def check_context(self, proper_subtype: bool) -> None:
         # Historically proper and non-proper subtypes were defined using different helpers
         # and different visitors. Check if flag values are such that we definitely support.
         if proper_subtype:
-            assert (
-                not self.ignore_type_params
-                and not self.ignore_pos_arg_names
-                and not self.ignore_declared_variance
-            )
+            assert not self.ignore_pos_arg_names and not self.ignore_declared_variance
         else:
             assert not self.erase_instances and not self.keep_erased_types
 
diff --git a/test-data/unit/check-inference.test b/test-data/unit/check-inference.test
index 45a833e5210c..dfd526b90747 100644
--- a/test-data/unit/check-inference.test
+++ b/test-data/unit/check-inference.test
@@ -3382,3 +3382,15 @@ class A:
 T = TypeVar("T")
 def type_or_callable(value: T, tp: Union[Type[T], Callable[[int], T]]) -> T: ...
 reveal_type(type_or_callable(A("test"), A))  # N: Revealed type is "__main__.A"
+
+[case testJoinWithAnyFallback]
+from unknown import X  # type: ignore[import]
+
+class A: ...
+class B(X, A): ...
+class C(B): ...
+class D(C): ...
+class E(D): ...
+
+reveal_type([E(), D()])  # N: Revealed type is "builtins.list[__main__.D]"
+reveal_type([D(), E()])  # N: Revealed type is "builtins.list[__main__.D]"