Reproduce #91

mypy-zope.ini

@@ -1,3 +1,4 @@
 [mypy]
 namespace_packages=True
+warn_unreachable=True
 plugins=mypy_zope:plugin

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>
+"""

tests/test_samples.py

@@ -26,6 +26,7 @@ def test_samples(samplefile, mypy_cache_dir):
     opts.show_traceback = True
     opts.namespace_packages = True
     opts.hide_error_codes = True
+    opts.warn_unreachable = True
     opts.plugins = ['mypy_zope:plugin']
     # Config file is needed to load plugins, it doesn't not exist and is not
     # supposed to.