fix: Override attribute values when merging stubs

Issue-mkdocstrings-751: mkdocstrings/mkdocstrings#751

Author: pawamoy

src/_griffe/merger.py

@@ -35,6 +35,8 @@ def _merge_function_stubs(function: Function, stubs: Function) -> None:
 def _merge_attribute_stubs(attribute: Attribute, stubs: Attribute) -> None:
     _merge_stubs_docstring(attribute, stubs)
     attribute.annotation = stubs.annotation
+    if stubs.value not in (None, "..."):
+        attribute.value = stubs.value
 
 
 def _merge_stubs_docstring(obj: Object, stubs: Object) -> None:

tests/test_merger.py

@@ -47,3 +47,16 @@ def test_merge_imports() -> None:
         },
     ) as pkg:
         assert set(pkg["mod"].imports) == {"abc", "collections"}
+
+
+def test_merge_attribute_values() -> None:
+    """Assert that attribute values are merged correctly."""
+    with temporary_visited_package(
+        "package",
+        {
+            "__init__.py": "import dynamic_all\n__all__ = dynamic_all()",
+            "__init__.pyi": "from ._hello import hello\n__all__ = ['hello']",
+            "_hello.py": "def hello() -> None:\n    '''Say hello.'''",
+        },
+    ) as pkg:
+        assert str(pkg["__all__"].value) == "['hello']"