core[patch]: configurable init params (#20070)

Proposed fix for #20061. need to test

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/core/tests/unit_tests/runnables/test_configurable.py

@@ -0,0 +1,85 @@
+from typing import Any, Dict, Optional
+
+from langchain_core.pydantic_v1 import Field, root_validator
+from langchain_core.runnables import (
+    ConfigurableField,
+    RunnableConfig,
+    RunnableSerializable,
+)
+
+
+class MyRunnable(RunnableSerializable[str, str]):
+    my_property: str = Field(alias="my_property_alias")
+    _my_hidden_property: str = ""
+
+    class Config:
+        allow_population_by_field_name = True
+
+    @root_validator(pre=True)
+    def my_error(cls, values: Dict[str, Any]) -> Dict[str, Any]:
+        if "_my_hidden_property" in values:
+            raise ValueError("Cannot set _my_hidden_property")
+        return values
+
+    @root_validator()
+    def build_extra(cls, values: Dict[str, Any]) -> Dict[str, Any]:
+        values["_my_hidden_property"] = values["my_property"]
+        return values
+
+    def invoke(self, input: str, config: Optional[RunnableConfig] = None) -> Any:
+        return input + self._my_hidden_property
+
+
+def test_doubly_set_configurable() -> None:
+    """Test that setting a configurable field with a default value works"""
+    runnable = MyRunnable(my_property="a")  # type: ignore
+    configurable_runnable = runnable.configurable_fields(
+        my_property=ConfigurableField(
+            id="my_property",
+            name="My property",
+            description="The property to test",
+        )
+    )
+
+    assert (
+        configurable_runnable.invoke(
+            "d", config=RunnableConfig(configurable={"my_property": "c"})
+        )
+        == "dc"
+    )
+
+
+def test_alias_set_configurable() -> None:
+    runnable = MyRunnable(my_property="a")  # type: ignore
+    configurable_runnable = runnable.configurable_fields(
+        my_property=ConfigurableField(
+            id="my_property_alias",
+            name="My property alias",
+            description="The property to test alias",
+        )
+    )
+
+    assert (
+        configurable_runnable.invoke(
+            "d", config=RunnableConfig(configurable={"my_property_alias": "c"})
+        )
+        == "dc"
+    )
+
+
+def test_field_alias_set_configurable() -> None:
+    runnable = MyRunnable(my_property_alias="a")
+    configurable_runnable = runnable.configurable_fields(
+        my_property=ConfigurableField(
+            id="my_property",
+            name="My property alias",
+            description="The property to test alias",
+        )
+    )
+
+    assert (
+        configurable_runnable.invoke(
+            "d", config=RunnableConfig(configurable={"my_property": "c"})
+        )
+        == "dc"
+    )