chore: adding a deprecation warning on the SentenceWindowRetriever (#…

…8597)

* linting

* improving message

* fixing header

* adding deprecation in the release notes

haystack/components/retrievers/sentence_window_retriever.py

@@ -2,6 +2,7 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+import warnings
 from typing import Any, Dict, List, Optional
 
 from haystack import Document, component, default_from_dict, default_to_dict
@@ -92,6 +93,13 @@ def __init__(self, document_store: DocumentStore, window_size: int = 3):
         self.window_size = window_size
         self.document_store = document_store
 
+        warnings.warn(
+            "The output of `context_documents` will change in the next release. Instead of a "
+            "List[List[Document]], the output will be a List[Document], where the documents are ordered by "
+            "`split_idx_start`.",
+            DeprecationWarning,
+        )
+
     @staticmethod
     def merge_documents_text(documents: List[Document]) -> str:
         """

releasenotes/notes/sentence-window-deprecation-b7db8efc56f33940.yaml

@@ -0,0 +1,3 @@
+deprecations:
+    |
+    "The output of `context_documents` will change in the next release. Instead of a List[List[Document]], the output will be a List[Document], where the documents are ordered by `split_idx_start`.",