Python: fix kernel_function decorator mutating shared Annotated metadata dicts

python/semantic_kernel/functions/kernel_function_decorator.py

@@ -152,9 +152,11 @@ def _parse_parameter(name: str, param: Any, default: Any) -> dict[str, Any]:
                     ret["description"] = meta
                 elif isinstance(meta, dict):
                     # only override from the metadata if it is not already set
-                    if "description" not in ret and (description := meta.pop("description", None)):
+                    # note: do not mutate the metadata dict itself, it is user-provided
+                    # and can be shared between multiple functions/parameters
+                    if "description" not in ret and (description := meta.get("description", None)):
                         ret["description"] = description
-                    ret.update(meta)
+                    ret.update({key: value for key, value in meta.items() if key != "description"})
                 else:
                     logger.debug(f"Unknown metadata type: {meta}")
         if hasattr(param, "__origin__"):

python/tests/unit/functions/test_kernel_function_decorators.py

@@ -280,3 +280,44 @@ def test_annotation_parsing(name, annotation, description, type_, is_required):
     assert description == annotation_dict.get("description")
     assert type_ == annotation_dict["type_"]
     assert is_required == annotation_dict["is_required"]
+
+
+def test_shared_annotation_metadata_dict_not_mutated():
+    """A dict used as Annotated metadata must not be mutated when parsed.
+
+    The same metadata dict can be reused across multiple kernel functions
+    (e.g. shared parameter docs); parsing one function's signature must not
+    remove the "description" key for the next function.
+    """
+    shared_meta = {"description": "shared description"}
+
+    @kernel_function
+    def func_one(arg: Annotated[int, shared_meta]) -> str:
+        return "one"
+
+    @kernel_function
+    def func_two(arg: Annotated[int, shared_meta]) -> str:
+        return "two"
+
+    # the user-provided dict is unchanged
+    assert shared_meta == {"description": "shared description"}
+
+    params_one = {p["name"]: p.get("description") for p in func_one.__kernel_function_parameters__}
+    params_two = {p["name"]: p.get("description") for p in func_two.__kernel_function_parameters__}
+
+    assert params_one["arg"] == "shared description"
+    assert params_two["arg"] == "shared description"
+
+
+def test_annotation_metadata_dict_other_keys_still_applied():
+    """Keys other than 'description' in a metadata dict must still be applied, without mutation."""
+    meta = {"description": "the description", "default_value": 42}
+
+    @kernel_function
+    def func(arg: Annotated[int, meta]) -> str:
+        return "ok"
+
+    assert meta == {"description": "the description", "default_value": 42}
+    param = func.__kernel_function_parameters__[0]
+    assert param["description"] == "the description"
+    assert param["default_value"] == 42