core: Two updates to chat model interface (#19684)

- .stream() and .astream() call on_llm_new_token, removing the need for
subclasses to do so. Backwards compatible because now we don't pass
run_manager into ._stream and ._astream
- .generate() and .agenerate() now handle `stream: bool` kwarg for
_generate and _agenerate. Subclasses handle this arg by delegating to
._stream(), now one less thing they need to do. Backwards compat because
this is an optional arg that we now never pass to the subclasses
- .generate() and .agenerate() now inspect callback handlers to decide
on a default value for stream:bool if not passed in. This auto enables
streaming when using astream_events and astream_log
- as a result of these three changes any usage of .astream_events and
.astream_log should now yield chat model stream events
- In future PRs we can update all subclasses to reflect these two things
now handled by base class, but in meantime all will continue to work

libs/core/langchain_core/language_models/chat_models.py

@@ -50,6 +50,7 @@ from langchain_core.outputs import (
 from langchain_core.prompt_values import ChatPromptValue, PromptValue, StringPromptValue
 from langchain_core.pydantic_v1 import Field, root_validator
 from langchain_core.runnables.config import ensure_config, run_in_executor
+from langchain_core.tracers.log_stream import LogStreamCallbackHandler
 
 if TYPE_CHECKING:
     from langchain_core.runnables import RunnableConfig
@@ -219,9 +220,10 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
             )
             generation: Optional[ChatGenerationChunk] = None
             try:
-                for chunk in self._stream(
-                    messages, stop=stop, run_manager=run_manager, **kwargs
-                ):
+                for chunk in self._stream(messages, stop=stop, **kwargs):
+                    run_manager.on_llm_new_token(
+                        cast(str, chunk.message.content), chunk=chunk
+                    )
                     chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                     yield chunk.message
                     if generation is None:
@@ -287,9 +289,11 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
             async for chunk in self._astream(
                 messages,
                 stop=stop,
-                run_manager=run_manager,
                 **kwargs,
             ):
+                await run_manager.on_llm_new_token(
+                    cast(str, chunk.message.content), chunk=chunk
+                )
                 chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
                 yield chunk.message
                 if generation is None:
@@ -585,6 +589,31 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
                 raise ValueError(
                     "Asked to cache, but no cache found at `langchain.cache`."
                 )
+        # If stream is not explicitly set, check if implicitly requested by
+        # astream_events() or astream_log(). Bail out if _stream not implemented
+        if type(self)._stream != BaseChatModel._stream and kwargs.pop(
+            "stream",
+            next(
+                (
+                    True
+                    for h in run_manager.handlers
+                    if isinstance(h, LogStreamCallbackHandler)
+                ),
+                False,
+            )
+            if run_manager
+            else False,
+        ):
+            chunks: List[ChatGenerationChunk] = []
+            for chunk in self._stream(messages, stop=stop, **kwargs):
+                if run_manager:
+                    run_manager.on_llm_new_token(
+                        cast(str, chunk.message.content), chunk=chunk
+                    )
+                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
+                chunks.append(chunk)
+            result = generate_from_stream(iter(chunks))
+        else:
             if inspect.signature(self._generate).parameters.get("run_manager"):
                 result = self._generate(
                     messages, stop=stop, run_manager=run_manager, **kwargs
@@ -634,6 +663,34 @@ class BaseChatModel(BaseLanguageModel[BaseMessage], ABC):
                 raise ValueError(
                     "Asked to cache, but no cache found at `langchain.cache`."
                 )
+        # If stream is not explicitly set, check if implicitly requested by
+        # astream_events() or astream_log(). Bail out if _astream not implemented
+        if (
+            type(self)._astream != BaseChatModel._astream
+            or type(self)._stream != BaseChatModel._stream
+        ) and kwargs.pop(
+            "stream",
+            next(
+                (
+                    True
+                    for h in run_manager.handlers
+                    if isinstance(h, LogStreamCallbackHandler)
+                ),
+                False,
+            )
+            if run_manager
+            else False,
+        ):
+            chunks: List[ChatGenerationChunk] = []
+            async for chunk in self._astream(messages, stop=stop, **kwargs):
+                if run_manager:
+                    await run_manager.on_llm_new_token(
+                        cast(str, chunk.message.content), chunk=chunk
+                    )
+                chunk.message.response_metadata = _gen_info_and_msg_metadata(chunk)
+                chunks.append(chunk)
+            result = generate_from_stream(iter(chunks))
+        else:
             if inspect.signature(self._agenerate).parameters.get("run_manager"):
                 result = await self._agenerate(
                     messages, stop=stop, run_manager=run_manager, **kwargs

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

@@ -1,4 +1,5 @@
 """Module that contains tests for runnable.astream_events API."""
+import sys
 from itertools import cycle
 from typing import Any, AsyncIterator, Dict, List, Sequence, cast
 
@@ -22,6 +23,7 @@ from langchain_core.retrievers import BaseRetriever
 from langchain_core.runnables import (
     ConfigurableField,
     Runnable,
+    RunnableConfig,
     RunnableLambda,
 )
 from langchain_core.runnables.history import RunnableWithMessageHistory
@@ -314,9 +316,7 @@ async def test_event_stream_with_lambdas_from_lambda() -> None:
 
 async def test_astream_events_from_model() -> None:
     """Test the output of a model."""
-    infinite_cycle = cycle(
-        [AIMessage(content="hello world!"), AIMessage(content="goodbye world!")]
-    )
+    infinite_cycle = cycle([AIMessage(content="hello world!")])
     # When streaming GenericFakeChatModel breaks AIMessage into chunks based on spaces
     model = (
         GenericFakeChatModel(messages=infinite_cycle)
@@ -373,6 +373,188 @@ async def test_astream_events_from_model() -> None:
         },
     ]
 
+    @RunnableLambda
+    def i_dont_stream(input: Any, config: RunnableConfig) -> Any:
+        if sys.version_info >= (3, 11):
+            return model.invoke(input)
+        else:
+            return model.invoke(input, config)
+
+    events = await _collect_events(i_dont_stream.astream_events("hello", version="v1"))
+    assert events == [
+        {
+            "data": {"input": "hello"},
+            "event": "on_chain_start",
+            "metadata": {},
+            "name": "i_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+        {
+            "data": {"input": {"messages": [[HumanMessage(content="hello")]]}},
+            "event": "on_chat_model_start",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content="hello")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content=" ")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content="world!")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {
+                "input": {"messages": [[HumanMessage(content="hello")]]},
+                "output": {
+                    "generations": [
+                        [
+                            {
+                                "generation_info": None,
+                                "message": AIMessage(content="hello world!"),
+                                "text": "hello world!",
+                                "type": "ChatGeneration",
+                            }
+                        ]
+                    ],
+                    "llm_output": None,
+                    "run": None,
+                },
+            },
+            "event": "on_chat_model_end",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessage(content="hello world!")},
+            "event": "on_chain_stream",
+            "metadata": {},
+            "name": "i_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+        {
+            "data": {"output": AIMessage(content="hello world!")},
+            "event": "on_chain_end",
+            "metadata": {},
+            "name": "i_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+    ]
+
+    @RunnableLambda
+    async def ai_dont_stream(input: Any, config: RunnableConfig) -> Any:
+        if sys.version_info >= (3, 11):
+            return await model.ainvoke(input)
+        else:
+            return await model.ainvoke(input, config)
+
+    events = await _collect_events(ai_dont_stream.astream_events("hello", version="v1"))
+    assert events == [
+        {
+            "data": {"input": "hello"},
+            "event": "on_chain_start",
+            "metadata": {},
+            "name": "ai_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+        {
+            "data": {"input": {"messages": [[HumanMessage(content="hello")]]}},
+            "event": "on_chat_model_start",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content="hello")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content=" ")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessageChunk(content="world!")},
+            "event": "on_chat_model_stream",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {
+                "input": {"messages": [[HumanMessage(content="hello")]]},
+                "output": {
+                    "generations": [
+                        [
+                            {
+                                "generation_info": None,
+                                "message": AIMessage(content="hello world!"),
+                                "text": "hello world!",
+                                "type": "ChatGeneration",
+                            }
+                        ]
+                    ],
+                    "llm_output": None,
+                    "run": None,
+                },
+            },
+            "event": "on_chat_model_end",
+            "metadata": {"a": "b"},
+            "name": "my_model",
+            "run_id": "",
+            "tags": ["my_model"],
+        },
+        {
+            "data": {"chunk": AIMessage(content="hello world!")},
+            "event": "on_chain_stream",
+            "metadata": {},
+            "name": "ai_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+        {
+            "data": {"output": AIMessage(content="hello world!")},
+            "event": "on_chain_end",
+            "metadata": {},
+            "name": "ai_dont_stream",
+            "run_id": "",
+            "tags": [],
+        },
+    ]
+
 
 async def test_event_stream_with_simple_chain() -> None:
     """Test as event stream."""