core: fix try_load_from_hub for older langchain versions load_chain (#19964)

libs/core/langchain_core/utils/loading.py

@@ -1,13 +1,28 @@
 """Utilities for loading configurations from langchain_core-hub."""
 
+import warnings
 from typing import Any
 
+from langchain_core._api.deprecation import deprecated
 
+
+@deprecated(
+    since="0.1.30",
+    removal="0.2",
+    message=(
+        "Using the hwchase17/langchain-hub "
+        "repo for prompts is deprecated. Please use "
+        "https://smith.langchain.com/hub instead."
+    ),
+)
 def try_load_from_hub(
     *args: Any,
     **kwargs: Any,
 ) -> Any:
-    raise RuntimeError(
+    warnings.warn(
         "Loading from the deprecated github-based Hub is no longer supported. "
         "Please use the new LangChain Hub at https://smith.langchain.com/hub instead."
     )
+    # return None, which indicates that we shouldn't load from old hub
+    # and might just be a filepath for e.g. load_chain
+    return None

libs/core/pyproject.toml

@@ -1,6 +1,6 @@
 [tool.poetry]
 name = "langchain-core"
-version = "0.1.39"
+version = "0.1.40"
 description = "Building applications with LLMs through composability"
 authors = []
 license = "MIT"