core[patch]: Correct type casting of annotations in _infer_arg_descriptions (#31181)

- **Description:** 
- In _infer_arg_descriptions, the annotations dictionary contains string
representations of types instead of actual typing objects. This causes
_is_annotated_type to fail, preventing the correct description from
being generated.
- This is a simple fix using the get_type_hints method, which resolves
the annotations properly and is supported across all Python versions.

  - **Issue:** #31051

---------

Co-authored-by: Eugene Yurtsev <[email protected]>

Author: keenborder786

libs/core/langchain_core/tools/base.py

@@ -5,6 +5,7 @@
 import functools
 import inspect
 import json
+import typing
 import warnings
 from abc import ABC, abstractmethod
 from inspect import signature
@@ -80,7 +81,7 @@ class SchemaAnnotationError(TypeError):
 
 
 def _is_annotated_type(typ: type[Any]) -> bool:
-    return get_origin(typ) is Annotated
+    return get_origin(typ) is typing.Annotated
 
 
 def _get_annotation_description(arg_type: type) -> str | None:
@@ -143,11 +144,7 @@ def _infer_arg_descriptions(
     error_on_invalid_docstring: bool = False,
 ) -> tuple[str, dict]:
     """Infer argument descriptions from a function's docstring."""
-    if hasattr(inspect, "get_annotations"):
-        # This is for python < 3.10
-        annotations = inspect.get_annotations(fn)
-    else:
-        annotations = getattr(fn, "__annotations__", {})
+    annotations = typing.get_type_hints(fn, include_extras=True)
     if parse_docstring:
         description, arg_descriptions = _parse_python_function_docstring(
             fn, annotations, error_on_invalid_docstring=error_on_invalid_docstring

libs/core/tests/unit_tests/test_tools.py

@@ -2711,3 +2711,24 @@ async def async_no_op(foo: int) -> str:
         "id": "call_0_82c17db8-95df-452f-a4c2-03f809022134",
         "type": "tool_call",
     }
+
+
+def test_tool_args_schema_with_annotated_type() -> None:
+    @tool
+    def test_tool(
+        query_fragments: Annotated[
+            list[str],
+            "A list of query fragments",
+        ],
+    ) -> list[str]:
+        """Search the Internet and retrieve relevant result items."""
+        return []
+
+    assert test_tool.args == {
+        "query_fragments": {
+            "description": "A list of query fragments",
+            "items": {"type": "string"},
+            "title": "Query Fragments",
+            "type": "array",
+        }
+    }