Import Optional if default param is None to match renderer (#164)

monkeytype/stubs.py

@@ -154,6 +154,8 @@ def get_imports_for_signature(sig: inspect.Signature) -> ImportMap:
     imports = ImportMap()
     for param in sig.parameters.values():
         param_imports = get_imports_for_annotation(param.annotation)
+        if not _is_optional(param.annotation) and param.default is None:
+            imports['typing'].add('Optional')
         imports.merge(param_imports)
     return_imports = get_imports_for_annotation(sig.return_annotation)
     imports.merge(return_imports)

tests/test_stubs.py

@@ -41,6 +41,7 @@
     StubIndexBuilder,
     build_module_stubs,
     get_imports_for_annotation,
+    get_imports_for_signature,
     render_signature,
     shrink_traced_types,
     update_signature_args,
@@ -1118,3 +1119,10 @@ def test_container_types(self, anno, expected):
 
     def test_nested_class(self):
         assert get_imports_for_annotation(Parent.Child) == {Parent.__module__: {'Parent'}}
+
+
+class TestGetImportsForSignature:
+    def test_default_none_parameter_imports(self):
+        stub = FunctionStub('test', inspect.signature(default_none_parameter), FunctionKind.MODULE)
+        expected = {'typing': {'Optional'}}
+        assert get_imports_for_signature(stub.signature) == expected