Introduce experimental feature warning (#2622)

src/py/flwr/client/grpc_rere_client/connection.py

@@ -16,7 +16,7 @@
 
 
 from contextlib import contextmanager
-from logging import DEBUG, ERROR, WARN
+from logging import DEBUG, ERROR
 from pathlib import Path
 from typing import Callable, Dict, Iterator, Optional, Tuple, Union, cast
 
@@ -28,7 +28,7 @@
 )
 from flwr.common import GRPC_MAX_MESSAGE_LENGTH
 from flwr.common.grpc import create_channel
-from flwr.common.logger import log
+from flwr.common.logger import log, warn_experimental_feature
 from flwr.proto.fleet_pb2 import (
     CreateNodeRequest,
     DeleteNodeRequest,
@@ -88,6 +88,8 @@ def grpc_request_response(
     create_node : Optional[Callable]
     delete_node : Optional[Callable]
     """
+    warn_experimental_feature("`grpc-rere`")
+
     if isinstance(root_certificates, str):
         root_certificates = Path(root_certificates).read_bytes()
 
@@ -99,14 +101,6 @@ def grpc_request_response(
     channel.subscribe(on_channel_state_change)
     stub = FleetStub(channel)
 
-    log(
-        WARN,
-        """
-        EXPERIMENTAL: `grpc-rere` is an experimental transport layer, it might change
-        considerably in future versions of Flower
-        """,
-    )
-
     # Necessary state to link TaskRes to TaskIns
     state: Dict[str, Optional[TaskIns]] = {KEY_TASK_INS: None}
 

src/py/flwr/common/logger.py

@@ -16,7 +16,7 @@
 
 
 import logging
-from logging import LogRecord
+from logging import WARN, LogRecord
 from logging.handlers import HTTPHandler
 from typing import Any, Dict, Optional, Tuple
 
@@ -97,3 +97,17 @@ def configure(
 
 logger = logging.getLogger(LOGGER_NAME)  # pylint: disable=invalid-name
 log = logger.log  # pylint: disable=invalid-name
+
+
+def warn_experimental_feature(name: str) -> None:
+    """Warn the user when they use an experimental feature."""
+    log(
+        WARN,
+        """
+        EXPERIMENTAL FEATURE: %s
+
+        This is an experimental feature. It could change significantly or be removed
+        entirely in future versions of Flower.
+        """,
+        name,
+    )