core[minor]: Add support for pydantic 2 to utility to get fields (#24899)

Add compatibility for pydantic 2 for a utility function.

This will help push some small changes to master, so they don't have to
be kept track of on a separate branch.

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

@@ -6,8 +6,13 @@ from unittest.mock import patch
 import pytest
 
 from langchain_core import utils
-from langchain_core.utils import check_package_version, guard_import
+from langchain_core.utils import (
+    check_package_version,
+    get_pydantic_field_names,
+    guard_import,
+)
 from langchain_core.utils._merge import merge_dicts
+from langchain_core.utils.pydantic import PYDANTIC_MAJOR_VERSION
 
 
 @pytest.mark.parametrize(
@@ -171,3 +176,46 @@ def test_guard_import_failure(
         f"Please install it with `pip install {pip_name}`."
     )
     assert exc_info.value.msg == err_msg
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 2, reason="Requires pydantic 2")
+def test_get_pydantic_field_names_v1_in_2() -> None:
+    from pydantic.v1 import BaseModel as PydanticV1BaseModel  # pydantic: ignore
+    from pydantic.v1 import Field  # pydantic: ignore
+
+    class PydanticV1Model(PydanticV1BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticV1Model)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 2, reason="Requires pydantic 2")
+def test_get_pydantic_field_names_v2_in_2() -> None:
+    from pydantic import BaseModel, Field  # pydantic: ignore
+
+    class PydanticModel(BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticModel)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected
+
+
+@pytest.mark.skipif(PYDANTIC_MAJOR_VERSION != 1, reason="Requires pydantic 1")
+def test_get_pydantic_field_names_v1() -> None:
+    from pydantic import BaseModel, Field  # pydantic: ignore
+
+    class PydanticModel(BaseModel):
+        field1: str
+        field2: int
+        alias_field: int = Field(alias="aliased_field")
+
+    result = get_pydantic_field_names(PydanticModel)
+    expected = {"field1", "field2", "aliased_field", "alias_field"}
+    assert result == expected