Add deprecation path for the old Loop module (Lightning-AI#13043)

Author: carmocca

CHANGELOG.md

@@ -96,9 +96,6 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 
 - Raise an error if there are insufficient training batches when using a float value of `limit_train_batches` ([#12885](https://github.com/PyTorchLightning/pytorch-lightning/pull/12885))
 
-
-- Changed `pytorch_lightning.core.lightning` to `pytorch_lightning.core.module` ([#12740](https://github.com/PyTorchLightning/pytorch-lightning/pull/12740))
-
 ### Deprecated
 
 - 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))
@@ -116,6 +113,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecated `pytorch_lightning.core.lightning.LightningModule` in favor of `pytorch_lightning.core.module.LightningModule` ([#12740](https://github.com/PyTorchLightning/pytorch-lightning/pull/12740))
 
 
+- Deprecated `pytorch_lightning.loops.base.Loop` in favor of `pytorch_lightning.loops.loop.Loop` ([#13043](https://github.com/PyTorchLightning/pytorch-lightning/pull/13043))
+
+
 - Deprecated `Trainer.reset_train_val_dataloaders()` in favor of `Trainer.reset_{train,val}_dataloader` ([#12184](https://github.com/PyTorchLightning/pytorch-lightning/pull/12184))
 
 ### Removed

pytorch_lightning/loops/__init__.py

@@ -11,11 +11,9 @@
 # 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 pytorch_lightning.loops.batch import ManualOptimization  # noqa: F401
+from pytorch_lightning.loops.loop import Loop  # noqa: F401 isort: skip (avoids circular imports)
 from pytorch_lightning.loops.batch import TrainingBatchLoop  # noqa: F401
 from pytorch_lightning.loops.dataloader import DataLoaderLoop, EvaluationLoop, PredictionLoop  # noqa: F401
 from pytorch_lightning.loops.epoch import EvaluationEpochLoop, PredictionEpochLoop, TrainingEpochLoop  # noqa: F401
 from pytorch_lightning.loops.fit_loop import FitLoop  # noqa: F401
-from pytorch_lightning.loops.loop import Loop  # noqa: F401
-from pytorch_lightning.loops.optimization.optimizer_loop import OptimizerLoop  # noqa: F401
+from pytorch_lightning.loops.optimization import ManualOptimization, OptimizerLoop  # noqa: F401

pytorch_lightning/loops/base.py

@@ -0,0 +1,25 @@
+# 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 pytorch_lightning.loops import Loop as NewLoop
+from pytorch_lightning.utilities.rank_zero import rank_zero_deprecation
+
+
+class Loop(NewLoop):
+    def __init__(self) -> None:
+        rank_zero_deprecation(
+            "pytorch_lightning.loops.base.Loop has been deprecated in v1.7"
+            " and will be removed in v1.9."
+            " Use the equivalent class from the pytorch_lightning.loops.loop.Loop class instead."
+        )
+        super().__init__()

tests/deprecated_api/test_remove_1-9.py

@@ -95,6 +95,23 @@ def test_old_lightningmodule_path():
         LightningModule()
 
 
+def test_old_loop_path():
+    from pytorch_lightning.loops.base import Loop
+
+    class MyLoop(Loop):
+        def advance(self):
+            ...
+
+        def done(self):
+            ...
+
+        def reset(self):
+            ...
+
+    with pytest.deprecated_call(match="pytorch_lightning.loops.base.Loop has been deprecated in v1.7"):
+        MyLoop()
+
+
 def test_lightningCLI_seed_everything_default_to_None_deprecation_warning():
     with mock.patch("sys.argv", ["any.py"]), pytest.deprecated_call(
         match="Setting `LightningCLI.seed_everything_default` to `None` is deprecated in v1.7 "