fix(langgraph): Add warning for incorrect node signature with mistyped config param (#5798)

Fixes: #5787

Ensures that if `config` is not typed as one of `RunanbleConfig` or
`Optional[RunnableConfig]` a warning is raised to help developers avoid
unexpected results at invocation time.

---------

Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>
Co-authored-by: Sydney Runkle <sydneymarierunkle@gmail.com>

libs/langgraph/langgraph/_internal/_runnable.py

@@ -4,6 +4,7 @@ import asyncio
 import enum
 import inspect
 import sys
+import warnings
 from collections.abc import (
     AsyncIterator,
     Awaitable,
@@ -303,6 +304,16 @@ class RunnableCallable(Runnable):
             if typ != (ANY_TYPE,) and p.annotation not in typ:
                 # A specific type is required, but the function annotation does
                 # not match the expected type.
+
+                # If this is a config parameter with incorrect typing, emit a warning
+                # because we used to support any type but are moving towards more correct typing
+                if kw == "config" and p.annotation != inspect.Parameter.empty:
+                    warnings.warn(
+                        f"The 'config' parameter should be typed as 'RunnableConfig' or "
+                        f"'RunnableConfig | None', not '{p.annotation}'. ",
+                        UserWarning,
+                        stacklevel=4,
+                    )
                 continue
 
             # If the kwarg is accepted by the function, store the key / runtime attribute to inject

libs/langgraph/tests/test_deprecation.py

@@ -1,3 +1,8 @@
+from __future__ import annotations
+
+import warnings
+from typing import Any, Optional
+
 import pytest
 from langchain_core.runnables import RunnableConfig
 from pytest_mock import MockerFixture
@@ -188,7 +193,9 @@ def test_deprecated_import() -> None:
         from langgraph.constants import PREVIOUS  # noqa: F401
 
 
-@pytest.mark.filterwarnings("ignore:`checkpoint_during` is deprecated")
+@pytest.mark.filterwarnings(
+    "ignore:`durability` has no effect when no checkpointer is present"
+)
 def test_checkpoint_during_deprecation_state_graph() -> None:
     class CheckDurability(TypedDict):
         durability: NotRequired[str]
@@ -228,3 +235,100 @@ def test_checkpoint_during_deprecation_state_graph() -> None:
     ):
         for chunk in graph.stream({}, checkpoint_during=False):  # type: ignore[arg-type]
             assert chunk["plain_node"]["durability"] == "exit"
+
+
+def test_config_parameter_incorrect_typing() -> None:
+    """Test that a warning is raised when config parameter is typed incorrectly."""
+    builder = StateGraph(PlainState)
+
+    # Test sync function with config: dict
+    with pytest.warns(
+        UserWarning,
+        match="The 'config' parameter should be typed as 'RunnableConfig' or 'RunnableConfig | None', not '.*dict.*'. ",
+    ):
+
+        def sync_node_with_dict_config(state: PlainState, config: dict) -> PlainState:
+            return state
+
+        builder.add_node(sync_node_with_dict_config)
+
+    # Test async function with config: dict
+    with pytest.warns(
+        UserWarning,
+        match="The 'config' parameter should be typed as 'RunnableConfig' or 'RunnableConfig | None', not '.*dict.*'. ",
+    ):
+
+        async def async_node_with_dict_config(
+            state: PlainState, config: dict
+        ) -> PlainState:
+            return state
+
+        builder.add_node(async_node_with_dict_config)
+
+    # Test with other incorrect types
+    with pytest.warns(
+        UserWarning,
+        match="The 'config' parameter should be typed as 'RunnableConfig' or 'RunnableConfig | None', not '.*Any.*'. ",
+    ):
+
+        def sync_node_with_any_config(state: PlainState, config: Any) -> PlainState:
+            return state
+
+        builder.add_node(sync_node_with_any_config)
+
+    with pytest.warns(
+        UserWarning,
+        match="The 'config' parameter should be typed as 'RunnableConfig' or 'RunnableConfig | None', not '.*Any.*'. ",
+    ):
+
+        async def async_node_with_any_config(
+            state: PlainState, config: Any
+        ) -> PlainState:
+            return state
+
+        builder.add_node(async_node_with_any_config)
+
+    with warnings.catch_warnings(record=True) as w:
+
+        def node_with_correct_config(
+            state: PlainState, config: RunnableConfig
+        ) -> PlainState:
+            return state
+
+        builder.add_node(node_with_correct_config)
+
+        def node_with_optional_config(
+            state: PlainState,
+            config: Optional[RunnableConfig],  # noqa: UP045
+        ) -> PlainState:
+            return state
+
+        builder.add_node(node_with_optional_config)
+
+        def node_with_untyped_config(state: PlainState, config) -> PlainState:
+            return state
+
+        builder.add_node(node_with_untyped_config)
+
+        async def async_node_with_correct_config(
+            state: PlainState, config: RunnableConfig
+        ) -> PlainState:
+            return state
+
+        builder.add_node(async_node_with_correct_config)
+
+        async def async_node_with_optional_config(
+            state: PlainState,
+            config: Optional[RunnableConfig],  # noqa: UP045
+        ) -> PlainState:
+            return state
+
+        builder.add_node(async_node_with_optional_config)
+
+        async def async_node_with_untyped_config(
+            state: PlainState, config
+        ) -> PlainState:
+            return state
+
+        builder.add_node(async_node_with_untyped_config)
+        assert len(w) == 0