Harrison/source docs (#1275)

Co-authored-by: Tushar Dhadiwal <tushardhadiwal@users.noreply.github.com>

langchain/chains/chat_vector_db/base.py

@@ -101,7 +101,7 @@ class ChatVectorDBChain(Chain, BaseModel):
         else:
             return {self.output_key: answer}
 
-    async def _acall(self, inputs: Dict[str, Any]) -> Dict[str, str]:
+    async def _acall(self, inputs: Dict[str, Any]) -> Dict[str, Any]:
         question = inputs["question"]
         chat_history_str = _get_chat_history(inputs["chat_history"])
         vectordbkwargs = inputs.get("vectordbkwargs", {})
@@ -119,4 +119,7 @@ class ChatVectorDBChain(Chain, BaseModel):
         new_inputs["question"] = new_question
         new_inputs["chat_history"] = chat_history_str
         answer, _ = await self.combine_docs_chain.acombine_docs(docs, **new_inputs)
-        return {self.output_key: answer}
+        if self.return_source_documents:
+            return {self.output_key: answer, "source_documents": docs}
+        else:
+            return {self.output_key: answer}