core[bug]: Fixing Missing Docstring Bug if no Docstring is provided in BaseModel class

libs/core/langchain_core/tools/base.py

@@ -34,6 +34,7 @@
     model_validator,
     validate_arguments,
 )
+from pydantic._internal._model_construction import ModelMetaclass
 from pydantic.v1 import BaseModel as BaseModelV1
 from pydantic.v1 import ValidationError as ValidationErrorV1
 from pydantic.v1 import validate_arguments as validate_arguments_v1
@@ -150,7 +151,10 @@ def _infer_arg_descriptions(
             fn, annotations, error_on_invalid_docstring=error_on_invalid_docstring
         )
     else:
-        description = inspect.getdoc(fn) or ""
+        if isinstance(fn, ModelMetaclass):
+            description = fn.__doc__ or ""
+        else:
+            description = inspect.getdoc(fn) or ""
         arg_descriptions = {}
     if parse_docstring:
         _validate_docstring_args_against_annotations(arg_descriptions, annotations)

libs/core/langchain_core/tools/structured.py

@@ -16,6 +16,7 @@
 )
 
 from pydantic import Field, SkipValidation
+from pydantic._internal._model_construction import ModelMetaclass
 from typing_extensions import override
 
 from langchain_core.callbacks import (
@@ -197,7 +198,10 @@ def add(a: int, b: int) -> int:
             description_ = source_function.__doc__ or None
         if description_ is None and args_schema:
             if isinstance(args_schema, type) and is_basemodel_subclass(args_schema):
-                description_ = args_schema.__doc__ or None
+                if isinstance(source_function, ModelMetaclass):
+                    description_ = args_schema.__doc__
+                else:
+                    description_ = args_schema.__doc__ or None
             elif isinstance(args_schema, dict):
                 description_ = args_schema.get("description")
             else:

libs/core/tests/unit_tests/test_tools.py

@@ -700,6 +700,12 @@ def test_missing_docstring() -> None:
         def search_api(query: str) -> str:
             return "API result"
 
+    @tool
+    class MyTool(BaseModel):
+        foo: str
+
+    assert MyTool.description == ""  # type: ignore[attr-defined]
+
 
 def test_create_tool_positional_args() -> None:
     """Test that positional arguments are allowed."""