Merge metadata + tags in config (#10762)

Think these should be a merge/update rather than overwrite

libs/langchain/langchain/schema/runnable/base.py

@@ -2035,6 +2035,11 @@ class RunnableBinding(Serializable, Runnable[Input, Output]):
         copy = cast(RunnableConfig, dict(self.config))
         if config:
             for key in config:
+                if key == "metadata":
+                    copy[key] = {**copy.get(key, {}), **config[key]}  # type: ignore
+                elif key == "tags":
+                    copy[key] = (copy.get(key) or []) + config[key]  # type: ignore
+                else:
                     # Even though the keys aren't literals this is correct
                     # because both dicts are same type
                     copy[key] = config[key] or copy.get(key)  # type: ignore

libs/langchain/tests/unit_tests/schema/runnable/test_runnable.py

@@ -7,7 +7,7 @@ from freezegun import freeze_time
 from pytest_mock import MockerFixture
 from syrupy import SnapshotAssertion
 
-from langchain.callbacks.manager import Callbacks
+from langchain.callbacks.manager import Callbacks, collect_runs
 from langchain.callbacks.tracers.base import BaseTracer
 from langchain.callbacks.tracers.schemas import Run
 from langchain.callbacks.tracers.stdout import ConsoleCallbackHandler
@@ -1271,6 +1271,31 @@ def test_with_config_with_config() -> None:
     ) == dumpd(llm.with_config({"metadata": {"a": "b"}, "tags": ["a-tag"]}))
 
 
+def test_metadata_is_merged() -> None:
+    """Test metadata and tags defined in with_config and at are merged/concatend."""
+
+    foo = RunnableLambda(lambda x: x).with_config({"metadata": {"my_key": "my_value"}})
+    expected_metadata = {
+        "my_key": "my_value",
+        "my_other_key": "my_other_value",
+    }
+    with collect_runs() as cb:
+        foo.invoke("hi", {"metadata": {"my_other_key": "my_other_value"}})
+        run = cb.traced_runs[0]
+    assert run.extra["metadata"] == expected_metadata
+
+
+def test_tags_are_appended() -> None:
+    """Test tags from with_config are concatenated with those in invocation."""
+
+    foo = RunnableLambda(lambda x: x).with_config({"tags": ["my_key"]})
+    with collect_runs() as cb:
+        foo.invoke("hi", {"tags": ["invoked_key"]})
+        run = cb.traced_runs[0]
+    assert isinstance(run.tags, list)
+    assert sorted(run.tags) == sorted(["my_key", "invoked_key"])
+
+
 def test_bind_bind() -> None:
     llm = FakeListLLM(responses=["i'm a textbot"])