From 5de7f2018000cbfed0fd57867a26d514bba56851 Mon Sep 17 00:00:00 2001
From: Andrey Lebedev <andrey@lebedev.lt>
Date: Fri, 10 Feb 2023 21:33:32 +0200
Subject: [PATCH] Attempt to reproduce #91

---
 tests/samples/isinstance_impl.py | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)
 create mode 100644 tests/samples/isinstance_impl.py

diff --git a/tests/samples/isinstance_impl.py b/tests/samples/isinstance_impl.py
new file mode 100644
index 0000000..242744d
--- /dev/null
+++ b/tests/samples/isinstance_impl.py
@@ -0,0 +1,29 @@
+from typing import Optional
+from zope.interface import implementer, Interface
+
+
+class IFoo(Interface):
+    ...
+
+
+@implementer(IFoo)
+class MyFoo:
+    ...
+
+
+def make_foo() -> Optional[IFoo]:
+    return MyFoo()
+
+
+x = make_foo()
+reveal_type(x)
+assert isinstance(x, MyFoo)
+
+# The code below should not be considered unreachable
+print("hello")
+
+"""
+<output>
+isinstance_impl.py:19: note: Revealed type is "Union[__main__.IFoo, None]"
+</output>
+"""