chore(core): deprecate chat message history (#40711)

Co-authored-by: open-swe[bot] <open-swe@users.noreply.github.com>

libs/core/langchain_core/chat_history.py

@@ -3,10 +3,11 @@
 from __future__ import annotations
 
 from abc import ABC, abstractmethod
-from typing import TYPE_CHECKING
+from typing import TYPE_CHECKING, Any
 
 from pydantic import BaseModel, Field
 
+from langchain_core._api import deprecated
 from langchain_core.messages import (
     AIMessage,
     BaseMessage,
@@ -19,6 +20,14 @@ if TYPE_CHECKING:
     from collections.abc import Sequence
 
 
+@deprecated(
+    since="1.6.4",
+    removal="2.0.0",
+    addendum=(
+        "See the short-term memory documentation for recommended alternatives: "
+        "https://docs.langchain.com/oss/python/langchain/short-term-memory"
+    ),
+)
 class BaseChatMessageHistory(ABC):
     """Abstract base class for storing chat message history.
 
@@ -96,6 +105,10 @@ class BaseChatMessageHistory(ABC):
     layer, so this operation is expected to incur some latency.
     """
 
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        """Initialize cooperatively to preserve multiple inheritance."""
+        super().__init__(*args, **kwargs)
+
     async def aget_messages(self) -> list[BaseMessage]:
         """Async version of getting messages.
 
@@ -199,6 +212,14 @@ class BaseChatMessageHistory(ABC):
         return get_buffer_string(self.messages)
 
 
+@deprecated(
+    since="1.6.4",
+    removal="2.0.0",
+    addendum=(
+        "See the short-term memory documentation for recommended alternatives: "
+        "https://docs.langchain.com/oss/python/langchain/short-term-memory"
+    ),
+)
 class InMemoryChatMessageHistory(BaseChatMessageHistory, BaseModel):
     """In memory implementation of chat message history.
 

libs/core/tests/unit_tests/chat_history/test_chat_history.py

@@ -1,9 +1,36 @@
 from collections.abc import Sequence
 
-from langchain_core.chat_history import BaseChatMessageHistory
+import pytest
+
+from langchain_core.chat_history import (
+    BaseChatMessageHistory,
+    InMemoryChatMessageHistory,
+)
 from langchain_core.messages import BaseMessage, HumanMessage
 
 
+@pytest.mark.parametrize(
+    "history_class", [BaseChatMessageHistory, InMemoryChatMessageHistory]
+)
+def test_chat_history_deprecated(history_class: type[BaseChatMessageHistory]) -> None:
+    assert "deprecated" in (history_class.__doc__ or "")
+    assert "https://docs.langchain.com/oss/python/langchain/short-term-memory" in (
+        history_class.__doc__ or ""
+    )
+
+
+async def test_in_memory_history_initialization() -> None:
+    messages = [HumanMessage(content="Hello")]
+    history = InMemoryChatMessageHistory(messages=messages)
+    assert await history.aget_messages() == messages
+    other_history = InMemoryChatMessageHistory()
+    await other_history.aadd_messages([HumanMessage(content="World")])
+    assert history.messages == messages
+    await history.aclear()
+    assert history.messages == []
+    assert other_history.messages == [HumanMessage(content="World")]
+
+
 def test_add_message_implementation_only() -> None:
     """Test implementation of add_message only."""