Merge branch 'master' into wip/acc

# Conflicts:
#	pytorch_lightning/accelerators/accelerator.py
#	pytorch_lightning/plugins/training_type/training_type_plugin.py

Author: SeanNaren

CHANGELOG.md

@@ -62,6 +62,9 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added reset dataloader hooks to Training Plugins and Accelerators ([#7861](https://github.com/PyTorchLightning/pytorch-lightning/pull/7861))
 
 
+- Added trainer stage hooks for Training Plugins and Accelerators ([#7864](https://github.com/PyTorchLightning/pytorch-lightning/pull/7864))
+
+
 ### Changed
 
 - Changed calling of `untoggle_optimizer(opt_idx)` out of the closure function ([#7563](https://github.com/PyTorchLightning/pytorch-lightning/pull/7563)

pytorch_lightning/accelerators/accelerator.py

@@ -591,12 +591,5 @@ def on_train_end(self) -> None:
     def on_train_batch_start(self, batch: Any, batch_idx: int, dataloader_idx: int) -> None:
         """
         Called in the training loop before anything happens for that batch.
-
-        If you return -1 here, you will skip training for the rest of the current epoch.
-
-        Args:
-            batch: The batched data as it is returned by the training DataLoader.
-            batch_idx: the index of the batch
-            dataloader_idx: the index of the dataloader
         """
         return self.training_type_plugin.on_train_batch_start(batch, batch_idx, dataloader_idx)

pytorch_lightning/plugins/training_type/training_type_plugin.py

@@ -366,12 +366,5 @@ def on_predict_end(self):
     def on_train_batch_start(self, batch: Any, batch_idx: int, dataloader_idx: int) -> None:
         """
         Called in the training loop before anything happens for that batch.
-
-        If you return -1 here, you will skip training for the rest of the current epoch.
-
-        Args:
-            batch: The batched data as it is returned by the training DataLoader.
-            batch_idx: the index of the batch
-            dataloader_idx: the index of the dataloader
         """
         pass