Deprecate stochastic_weight_avg from the Trainer constructor

CHANGELOG.md

@@ -277,6 +277,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Deprecate `LightningDistributed` and move the broadcast logic to `DDPPlugin` and `DDPSpawnPlugin` directly ([#9691](https://github.com/PyTorchLightning/pytorch-lightning/pull/9691))
 
 
+- Deprecated passing `stochastic_weight_avg` from the `Trainer` constructor in favor of adding the `StochasticWeightAveraging` callback directly to the list of callbacks ([#8989](https://github.com/PyTorchLightning/pytorch-lightning/pull/8989))
+
+
 ### Removed
 
 - Removed deprecated `metrics` ([#8586](https://github.com/PyTorchLightning/pytorch-lightning/pull/8586/))

pytorch_lightning/trainer/connectors/callback_connector.py

@@ -52,6 +52,12 @@ def on_trainer_init(
         # init folder paths for checkpoint + weights save callbacks
         self.trainer._default_root_dir = default_root_dir or os.getcwd()
         self.trainer._weights_save_path = weights_save_path or self.trainer._default_root_dir
+        if stochastic_weight_avg:
+            rank_zero_deprecation(
+                "Setting `Trainer(stochastic_weight_avg=True)` is deprecated in v1.5 and will be removed in v1.7."
+                " Please pass `pytorch_lightning.callbacks.stochastic_weight_avg.StochasticWeightAveraging`"
+                " directly to the Trainer's `callbacks` argument instead."
+            )
         self.trainer._stochastic_weight_avg = stochastic_weight_avg
 
         # init callbacks

pytorch_lightning/trainer/trainer.py

@@ -375,6 +375,10 @@ def __init__(
             stochastic_weight_avg: Whether to use `Stochastic Weight Averaging (SWA)
                 <https://pytorch.org/blog/pytorch-1.6-now-includes-stochastic-weight-averaging/>`_.
 
+                .. deprecated:: v1.5
+                    ``stochastic_weight_avg`` has been deprecated in v1.5 and will be removed in v1.7.
+                    Please pass :class:`~pytorch_lightning.callbacks.stochastic_weight_avg.StochasticWeightAveraging`
+                    directly to the Trainer's ``callbacks`` argument instead.
         """
         super().__init__()
         Trainer._log_api_event("init")

tests/deprecated_api/test_remove_1-7.py

@@ -117,6 +117,11 @@ def test_v1_7_0_trainer_prepare_data_per_node(tmpdir):
         _ = Trainer(prepare_data_per_node=False)
 
 
+def test_v1_7_0_stochastic_weight_avg_trainer_constructor(tmpdir):
+    with pytest.deprecated_call(match=r"Setting `Trainer\(stochastic_weight_avg=True\)` is deprecated in v1.5"):
+        _ = Trainer(stochastic_weight_avg=True)
+
+
 def test_v1_7_0_deprecated_on_task_dataloader(tmpdir):
     class CustomBoringModel(BoringModel):
         def on_train_dataloader(self):