core[patch]: fix empty OpenAI tools when strict=True (#26287)

Fix #26232

---------

Co-authored-by: Eugene Yurtsev <eyurtsev@gmail.com>

libs/core/langchain_core/utils/function_calling.py

@@ -605,9 +605,13 @@ def _recursive_set_additional_properties_false(
     schema: Dict[str, Any],
 ) -> Dict[str, Any]:
     if isinstance(schema, dict):
-        # Check if 'required' is a key at the current level
+        # Check if 'required' is a key at the current level or if the schema is empty,
-        if "required" in schema:
+        # in which case additionalProperties still needs to be specified.
+        if "required" in schema or (
+            "properties" in schema and not schema["properties"]
+        ):
             schema["additionalProperties"] = False
+
         # Recursively check 'properties' and 'items' if they exist
         if "properties" in schema:
             for value in schema["properties"].values():

libs/core/tests/unit_tests/utils/test_function_calling.py

@@ -793,3 +793,22 @@ def test_convert_union_type_py_39() -> None:
     assert result["parameters"]["properties"]["input"] == {
         "anyOf": [{"type": "integer"}, {"type": "number"}]
     }
+
+
+def test_convert_to_openai_function_no_args() -> None:
+    @tool
+    def empty_tool() -> str:
+        """No args"""
+        return "foo"
+
+    actual = convert_to_openai_function(empty_tool, strict=True)
+    assert actual == {
+        "name": "empty_tool",
+        "description": "No args",
+        "parameters": {
+            "properties": {},
+            "additionalProperties": False,
+            "type": "object",
+        },
+        "strict": True,
+    }