Restore compatibility with custom checkpointer classes created in prior versions (#5103)

libs/checkpoint-postgres/uv.lock

@@ -328,6 +328,7 @@ dev = [
     { name = "mypy" },
     { name = "numpy" },
     { name = "pandas" },
+    { name = "pandas-stubs", specifier = ">=2.2.2.240807" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
     { name = "pytest-mock" },

libs/checkpoint-sqlite/uv.lock

@@ -340,6 +340,7 @@ dev = [
     { name = "mypy" },
     { name = "numpy" },
     { name = "pandas" },
+    { name = "pandas-stubs", specifier = ">=2.2.2.240807" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
     { name = "pytest-mock" },

libs/checkpoint/langgraph/checkpoint/base/__init__.py

@@ -1,8 +1,10 @@
 from __future__ import annotations
 
 from collections.abc import AsyncIterator, Iterator, Sequence
+from inspect import signature
 from typing import (  # noqa: UP035
     Any,
+    ClassVar,
     Generic,
     Literal,
     NamedTuple,
@@ -116,8 +118,19 @@ class BaseCheckpointSaver(Generic[V]):
         versions to avoid blocking the main thread.
     """
 
+    _get_next_version_legacy: ClassVar[bool] = False
+    """Flag indicating if get_next_version method is legacy (takes two parameters)."""
+
     serde: SerializerProtocol = JsonPlusSerializer()
 
+    def __init_subclass__(cls) -> None:
+        cls._get_next_version_legacy = (
+            len(signature(cls.get_next_version).parameters) > 2  # self + current
+            if hasattr(cls, "get_next_version")
+            else False
+        )
+        return super().__init_subclass__()
+
     def __init__(
         self,
         *,

libs/checkpoint/langgraph/checkpoint/serde/types.py

@@ -1,4 +1,13 @@
-from typing import Any, Protocol, TypeVar, runtime_checkable
+from collections.abc import Sequence
+from typing import (
+    Any,
+    Optional,
+    Protocol,
+    TypeVar,
+    runtime_checkable,
+)
+
+from typing_extensions import Self
 
 ERROR = "__error__"
 SCHEDULED = "__scheduled__"
@@ -11,6 +20,25 @@ Update = TypeVar("Update", contravariant=True)
 C = TypeVar("C")
 
 
+class ChannelProtocol(Protocol[Value, Update, C]):
+    # Mirrors langgraph.channels.base.BaseChannel
+    @property
+    def ValueType(self) -> Any: ...
+
+    @property
+    def UpdateType(self) -> Any: ...
+
+    def checkpoint(self) -> Optional[C]: ...
+
+    def from_checkpoint(self, checkpoint: Optional[C]) -> Self: ...
+
+    def update(self, values: Sequence[Update]) -> bool: ...
+
+    def get(self) -> Value: ...
+
+    def consume(self) -> bool: ...
+
+
 @runtime_checkable
 class SendProtocol(Protocol):
     # Mirrors langgraph.constants.Send

libs/checkpoint/pyproject.toml

@@ -31,6 +31,7 @@ dev = [
   "dataclasses-json",
   "numpy",
   "pandas",
+  "pandas-stubs>=2.2.2.240807",
 ]
 
 [tool.hatch.build.targets.wheel]

libs/langgraph/langgraph/pregel/loop.py

@@ -28,6 +28,7 @@ from typing_extensions import ParamSpec, Self
 
 from langgraph.cache.base import BaseCache
 from langgraph.channels.base import BaseChannel
+from langgraph.channels.last_value import LastValue
 from langgraph.checkpoint.base import (
     EXCLUDED_METADATA_KEYS,
     WRITES_IDX_MAP,
@@ -941,7 +942,13 @@ class SyncPregelLoop(PregelLoop, AbstractContextManager):
         )
         self.stack = ExitStack()
         if checkpointer:
-            self.checkpointer_get_next_version = checkpointer.get_next_version
+            if checkpointer._get_next_version_legacy:
+                empty_channel: LastValue[Any] = LastValue(Any)
+                self.checkpointer_get_next_version = (
+                    lambda c: checkpointer.get_next_version(c, empty_channel)  # type: ignore[call-arg]
+                )
+            else:
+                self.checkpointer_get_next_version = checkpointer.get_next_version
             self.checkpointer_put_writes = checkpointer.put_writes
             self.checkpointer_put_writes_accepts_task_path = (
                 signature(checkpointer.put_writes).parameters.get("task_path")
@@ -1114,7 +1121,13 @@ class AsyncPregelLoop(PregelLoop, AbstractAsyncContextManager):
         )
         self.stack = AsyncExitStack()
         if checkpointer:
-            self.checkpointer_get_next_version = checkpointer.get_next_version
+            if checkpointer._get_next_version_legacy:
+                empty_channel: LastValue[Any] = LastValue(Any)
+                self.checkpointer_get_next_version = (
+                    lambda c: checkpointer.get_next_version(c, empty_channel)  # type: ignore[call-arg]
+                )
+            else:
+                self.checkpointer_get_next_version = checkpointer.get_next_version
             self.checkpointer_put_writes = checkpointer.aput_writes
             self.checkpointer_put_writes_accepts_task_path = (
                 signature(checkpointer.aput_writes).parameters.get("task_path")

libs/langgraph/uv.lock

@@ -1330,6 +1330,7 @@ dev = [
     { name = "mypy" },
     { name = "numpy" },
     { name = "pandas" },
+    { name = "pandas-stubs", specifier = ">=2.2.2.240807" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
     { name = "pytest-mock" },

libs/prebuilt/uv.lock

@@ -391,6 +391,7 @@ dev = [
     { name = "mypy" },
     { name = "numpy" },
     { name = "pandas" },
+    { name = "pandas-stubs", specifier = ">=2.2.2.240807" },
     { name = "pytest" },
     { name = "pytest-asyncio" },
     { name = "pytest-mock" },