Add .pick and .assign methods to Runnable (#15229)

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libs/langchain/langchain/chains/history_aware_retriever.py

@@ -35,13 +35,13 @@ def create_history_aware_retriever(
             # pip install -U langchain langchain-community
 
             from langchain_community.chat_models import ChatOpenAI
-            from langchain.chains import create_chat_history_retriever
+            from langchain.chains import create_history_aware_retriever
             from langchain import hub
 
             rephrase_prompt = hub.pull("langchain-ai/chat-langchain-rephrase")
             llm = ChatOpenAI()
             retriever = ...
-            chat_retriever_chain = create_chat_retriever_chain(
+            chat_retriever_chain = create_history_aware_retriever(
                 llm, retriever, rephrase_prompt
             )
 

libs/langchain/langchain/chains/retrieval.py

@@ -64,8 +64,7 @@ def create_retrieval_chain(
         RunnablePassthrough.assign(
             context=retrieval_docs.with_config(run_name="retrieve_documents"),
             chat_history=lambda x: x.get("chat_history", []),
-        )
-        | RunnablePassthrough.assign(answer=combine_docs_chain)
+        ).assign(answer=combine_docs_chain)
     ).with_config(run_name="retrieval_chain")
 
     return retrieval_chain