fix: Fix inheritance logic when intermediate class without member is present

Issue-4: #4
PR-5: #5
Co-authored-by: Timothée Mazzucotelli <dev@pawamoy.fr>

Author: thomasmarwitz

src/griffe_inherited_docstrings/extension.py

@@ -13,8 +13,10 @@
 
 def _docstring_above(obj: Object) -> Docstring | None:
     with contextlib.suppress(IndexError, KeyError):
-        parent = obj.parent.mro()[0]  # type: ignore[union-attr]
-        return parent.members[obj.name].docstring
+        for parent in obj.parent.mro():  # type: ignore[union-attr]
+            # Fetch docstring from first parent that has the member.
+            if obj.name in parent.members:
+                return parent.members[obj.name].docstring
     return None
 
 
@@ -35,7 +37,7 @@ def _inherit_docstrings(obj: Object, *, merge: bool = False, seen: set[str] | No
 
     elif obj.is_class:
         # Recursively handle top-most parents first.
-        # It means that we can just check the first parent
+        # It means that we can just check the first parent with the member
         # when actually inheriting (and optionally merging) a docstring,
         # since the docstrings of the other parents have already been inherited.
         for parent in reversed(obj.mro()):  # type: ignore[attr-defined]

tests/test_extension.py

@@ -87,3 +87,32 @@ def meth(self):
         assert package["D.meth"].docstring.value == package["A.meth"].docstring.value + "\n\n" + f"{meth_doc} D."
         assert package["E.attr"].docstring.value == package["D.attr"].docstring.value + "\n\n" + f"{attr_doc} E."
         assert package["E.meth"].docstring.value == package["D.meth"].docstring.value + "\n\n" + f"{meth_doc} E."
+
+
+def test_inherit_and_merge_docstrings_intermediate_class() -> None:
+    """Inherit and merge docstrings from parent classes with an intermediate class.
+
+    It is important that the intermediate class doesn't have the member for which
+    docstring inheritance should be performed.
+    """
+    with temporary_visited_package(
+        "package",
+        modules={
+            "__init__.py": """
+                class Parent:
+                    def method(self):
+                        '''Parent.'''
+
+                class Intermediate(Parent):
+                    # This shouldn't break the inherting of docstrings.
+                    # See https://github.com/mkdocstrings/griffe-inherited-docstrings/issues/4.
+                    ...
+
+                class Child(Intermediate):
+                    def method(self):
+                        '''Child.'''
+            """,
+        },
+        extensions=Extensions(InheritDocstringsExtension(merge=True)),
+    ) as package:
+        assert package["Child.method"].docstring.value == "Parent.\n\nChild."