core[patch]: fix runnable history and add docs (#22283)

libs/core/langchain_core/runnables/history.py

@@ -372,6 +372,7 @@ def _get_input_messages(
     ) -> List[BaseMessage]:
         from langchain_core.messages import BaseMessage
 
+        # If dictionary, try to pluck the single key representing messages
         if isinstance(input_val, dict):
             if self.input_messages_key:
                 key = self.input_messages_key
@@ -381,13 +382,25 @@ def _get_input_messages(
                 key = "input"
             input_val = input_val[key]
 
+        # If value is a string, convert to a human message
         if isinstance(input_val, str):
             from langchain_core.messages import HumanMessage
 
             return [HumanMessage(content=input_val)]
+        # If value is a single message, convert to a list
         elif isinstance(input_val, BaseMessage):
             return [input_val]
+        # If value is a list or tuple...
         elif isinstance(input_val, (list, tuple)):
+            # Handle empty case
+            if len(input_val) == 0:
+                return list(input_val)
+            # If is a list of list, then return the first value
+            # This occurs for chat models - since we batch inputs
+            if isinstance(input_val[0], list):
+                if len(input_val) != 1:
+                    raise ValueError()
+                return input_val[0]
             return list(input_val)
         else:
             raise ValueError(
@@ -400,6 +413,7 @@ def _get_output_messages(
     ) -> List[BaseMessage]:
         from langchain_core.messages import BaseMessage
 
+        # If dictionary, try to pluck the single key representing messages
         if isinstance(output_val, dict):
             if self.output_messages_key:
                 key = self.output_messages_key
@@ -418,6 +432,7 @@ def _get_output_messages(
             from langchain_core.messages import AIMessage
 
             return [AIMessage(content=output_val)]
+        # If value is a single message, convert to a list
         elif isinstance(output_val, BaseMessage):
             return [output_val]
         elif isinstance(output_val, (list, tuple)):
@@ -431,7 +446,10 @@ def _enter_history(self, input: Any, config: RunnableConfig) -> List[BaseMessage
 
         if not self.history_messages_key:
             # return all messages
-            messages += self._get_input_messages(input)
+            input_val = (
+                input if not self.input_messages_key else input[self.input_messages_key]
+            )
+            messages += self._get_input_messages(input_val)
         return messages
 
     async def _aenter_history(
@@ -454,7 +472,6 @@ def _exit_history(self, run: Run, config: RunnableConfig) -> None:
         # Get the input messages
         inputs = load(run.inputs)
         input_messages = self._get_input_messages(inputs)
-
         # If historic messages were prepended to the input messages, remove them to
         # avoid adding duplicate messages to history.
         if not self.history_messages_key:

libs/core/langchain_core/tracers/base.py

@@ -48,7 +48,9 @@ class BaseTracer(BaseCallbackHandler, ABC):
     def __init__(
         self,
         *,
-        _schema_format: Literal["original", "streaming_events"] = "original",
+        _schema_format: Literal[
+            "original", "streaming_events", "original+chat"
+        ] = "original",
         **kwargs: Any,
     ) -> None:
         """Initialize the tracer.
@@ -63,6 +65,8 @@ def __init__(
                    for internal usage. It will likely change in the future, or
                    be deprecated entirely in favor of a dedicated async tracer
                    for streaming events.
+                - 'original+chat' is a format that is the same as 'original'
+                   except it does NOT raise an attribute error on_chat_model_start
             kwargs: Additional keyword arguments that will be passed to
                     the super class.
         """
@@ -163,7 +167,7 @@ def on_chat_model_start(
         **kwargs: Any,
     ) -> Run:
         """Start a trace for an LLM run."""
-        if self._schema_format != "streaming_events":
+        if self._schema_format not in ("streaming_events", "original+chat"):
             # Please keep this un-implemented for backwards compatibility.
             # When it's unimplemented old tracers that use the "original" format
             # fallback on the on_llm_start method implementation if they
@@ -360,7 +364,7 @@ def on_chain_start(
 
     def _get_chain_inputs(self, inputs: Any) -> Any:
         """Get the inputs for a chain run."""
-        if self._schema_format == "original":
+        if self._schema_format in ("original", "original+chat"):
             return inputs if isinstance(inputs, dict) else {"input": inputs}
         elif self._schema_format == "streaming_events":
             return {
@@ -371,7 +375,7 @@ def _get_chain_inputs(self, inputs: Any) -> Any:
 
     def _get_chain_outputs(self, outputs: Any) -> Any:
         """Get the outputs for a chain run."""
-        if self._schema_format == "original":
+        if self._schema_format in ("original", "original+chat"):
             return outputs if isinstance(outputs, dict) else {"output": outputs}
         elif self._schema_format == "streaming_events":
             return {
@@ -436,7 +440,7 @@ def on_tool_start(
         if metadata:
             kwargs.update({"metadata": metadata})
 
-        if self._schema_format == "original":
+        if self._schema_format in ("original", "original+chat"):
             inputs = {"input": input_str}
         elif self._schema_format == "streaming_events":
             inputs = {"input": inputs}

libs/core/langchain_core/tracers/log_stream.py

@@ -482,7 +482,7 @@ def _get_standardized_inputs(
 
 
 def _get_standardized_outputs(
-    run: Run, schema_format: Literal["original", "streaming_events"]
+    run: Run, schema_format: Literal["original", "streaming_events", "original+chat"]
 ) -> Optional[Any]:
     """Extract standardized output from a run.
 

libs/core/langchain_core/tracers/root_listeners.py

@@ -22,7 +22,7 @@ def __init__(
         on_end: Optional[Listener],
         on_error: Optional[Listener],
     ) -> None:
-        super().__init__()
+        super().__init__(_schema_format="original+chat")
 
         self.config = config
         self._arg_on_start = on_start

libs/core/tests/unit_tests/fake/memory.py

@@ -17,6 +17,8 @@ class ChatMessageHistory(BaseChatMessageHistory, BaseModel):
 
     def add_message(self, message: BaseMessage) -> None:
         """Add a self-created message to the store"""
+        if not isinstance(message, BaseMessage):
+            raise ValueError
         self.messages.append(message)
 
     def clear(self) -> None: