fix: Forward class attribute docstrings to instances

Issue #128: #128
PR #135: #135

src/griffe/agents/visitor.py

@@ -590,6 +590,12 @@ def handle_attribute(
                 if isinstance(node.parent, (ast.If, ast.ExceptHandler)):  # type: ignore[union-attr]
                     continue  # prefer "no-exception" case
 
+                parent.members[name].labels |= labels
+
+                # forward previous docstring instead of erasing it
+                if parent.members[name].docstring and not docstring:
+                    docstring = parent.members[name].docstring
+
             attribute = Attribute(
                 name=name,
                 value=value,

tests/test_visitor.py

@@ -279,3 +279,21 @@ def cached_prop(self) -> int:
         assert "property" in module["C.prop"].labels
         assert module["C.cached_prop"].is_attribute
         assert "cached" in module["C.cached_prop"].labels
+
+
+def test_forward_docstrings() -> None:
+    """Assert docstrings of class attributes are forwarded to instance assignments.
+
+    This is a regression test for https://github.com/mkdocstrings/griffe/issues/128.
+    """
+    with temporary_visited_module(
+        '''
+        class C:
+            attr: int
+            """This is a non-empty docstring."""
+
+            def __init__(self, attr: int) -> None:
+                self.attr = attr
+        '''
+    ) as module:
+        assert module["C.attr"].docstring