Add deprecation path for the old Callback module (#13031)

CHANGELOG.md

@@ -104,6 +104,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated `pytorch_lightning.loggers.base.LightningLoggerBase` in favor of `pytorch_lightning.loggers.logger.Logger`, and deprecated `pytorch_lightning.loggers.base` in favor of `pytorch_lightning.loggers.logger` ([#120148](https://github.com/PyTorchLightning/pytorch-lightning/pull/12014))
 
 
+- Deprecated `pytorch_lightning.callbacks.base.Callback` in favor of `pytorch_lightning.callbacks.callback.Callback` ([#13031](https://github.com/PyTorchLightning/pytorch-lightning/pull/13031))
+
 
 - Deprecated `num_processes`, `gpus`, `tpu_cores,` and `ipus` from the `Trainer` constructor in favor of using the `accelerator` and `devices` arguments ([#11040](https://github.com/PyTorchLightning/pytorch-lightning/pull/11040))
 

pytorch_lightning/callbacks/base.py

@@ -0,0 +1,27 @@
+# Copyright The PyTorch Lightning team.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from typing import Any
+
+from pytorch_lightning.callbacks.callback import Callback as NewCallback
+from pytorch_lightning.utilities import rank_zero_deprecation
+
+
+class Callback(NewCallback):
+    def __init__(self, *args: Any, **kwargs: Any) -> None:
+        rank_zero_deprecation(
+            "pytorch_lightning.callbacks.base.Callback has been deprecated in v1.7"
+            " and will be removed in v1.9."
+            " Use the equivalent class from the pytorch_lightning.callbacks.callback.Callback class instead."
+        )
+        super().__init__(*args, **kwargs)

tests/deprecated_api/test_remove_1-9.py

@@ -100,3 +100,12 @@ def test_lightningCLI_seed_everything_default_to_None_deprecation_warning():
         "and will be removed in v1.9. Set it to `False` instead."
     ):
         LightningCLI(LightningModule, run=False, seed_everything_default=None)
+
+
+def test_old_callback_path():
+    from pytorch_lightning.callbacks.base import Callback
+
+    with pytest.deprecated_call(
+        match="pytorch_lightning.callbacks.base.Callback has been deprecated in v1.7" " and will be removed in v1.9."
+    ):
+        Callback()