Add test case `testNarrowingIsInstanceNoIntersectionWithFinalTypeAndN…

…oneType` and modify (fix?) the second algorithm tried in `conditional_types_with_intersection`.
python · hauntsaninja · Jan 14, 2024 · Oct 23, 2023 · Oct 23, 2023 · Oct 24, 2023
commit fe12f7d1a62a66c45ba23c45965e4064117a2fff
diff --git a/mypy/checker.py b/mypy/checker.py
@@ -7120,9 +7120,10 @@ def conditional_types_with_intersection(
         possible_target_types = []
         for tr in type_ranges:
             item = get_proper_type(tr.item)
-            if not isinstance(item, Instance) or tr.is_upper_bound:
-                return yes_type, no_type
-            possible_target_types.append(item)
+            if isinstance(item, Instance):
+                possible_target_types.append(item)
+        if not possible_target_types:
+            return yes_type, no_type
 
         out = []
         errors: list[tuple[str, str]] = []

diff --git a/test-data/unit/check-narrowing.test b/test-data/unit/check-narrowing.test
@@ -2067,3 +2067,25 @@ def f(cls: Type[Union[None, int]]) -> None:
     else:
         reveal_type(cls)  # N: Revealed type is "Type[builtins.int]"
 [builtins fixtures/isinstance.pyi]
+
+[case testNarrowingIsInstanceNoIntersectionWithFinalTypeAndNoneType]
+# flags: --warn-unreachable --python-version 3.10
+
+from types import NoneType
+from typing import final
+
+class X: ...
+class Y: ...
+@final
+class Z: ...
+
+x: X
+
+if isinstance(x, (Y, Z)):
+    reveal_type(x)  # N: Revealed type is "__main__.<subclass of "X" and "Y">"
+if isinstance(x, (Y, NoneType)):
+    reveal_type(x)  # N: Revealed type is "__main__.<subclass of "X" and "Y">1"
+if isinstance(x, (Y, Z, NoneType)):
+    reveal_type(x)  # N: Revealed type is "__main__.<subclass of "X" and "Y">2"
+
+[builtins fixtures/isinstance.pyi]