Support string return annotation

Author: clayote

src/attr/_make.py

@@ -586,7 +586,6 @@ def _make_cached_property_uncached(original_cached_property_func, cls):
     annotation = inspect.signature(
         original_cached_property_func
     ).return_annotation
-    assert not isinstance(annotation, str)
     if annotation is inspect.Parameter.empty:
         defline = f"def {name}(self):"
     elif isinstance(

tests/test_slots.py

@@ -780,6 +780,15 @@ def f(self) -> functools.partial:
         return_annotation = eval(return_annotation)
     assert return_annotation is functools.partial
 
+    @attr.s(slots=True)
+    class C:
+        @functools.cached_property
+        def f(self) -> "wow":
+            return "wow"
+
+    return_annotation = inspect.signature(C.f.fget).return_annotation
+    assert return_annotation == "wow"
+
 
 def test_slots_cached_property_has_docstring():
     """