[bugfix] Add support for omegaconf and tpu (#6741)

* fix_hydra

* update changelog

Co-authored-by: Your Name <you@example.com>

CHANGELOG.md

@@ -226,6 +226,8 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Added Autocast in validation, test and predict modes for Native AMP ([#6565](https://github.com/PyTorchLightning/pytorch-lightning/pull/6565))
 
 
+- Fixed resolve a bug with omegaconf and xm.save ([#6741](https://github.com/PyTorchLightning/pytorch-lightning/pull/6741))
+
 ## [1.2.4] - 2021-03-16
 
 ### Changed

pytorch_lightning/plugins/training_type/tpu_spawn.py

@@ -23,10 +23,11 @@
 from pytorch_lightning.plugins.training_type.ddp_spawn import DDPSpawnPlugin
 from pytorch_lightning.plugins.training_type.utils import on_colab_kaggle
 from pytorch_lightning.trainer.states import TrainerState
-from pytorch_lightning.utilities import _TPU_AVAILABLE, rank_zero_warn
+from pytorch_lightning.utilities import _TPU_AVAILABLE, rank_zero_warn, _OMEGACONF_AVAILABLE
 from pytorch_lightning.utilities.distributed import rank_zero_only, ReduceOp
 from pytorch_lightning.utilities.exceptions import MisconfigurationException
 from pytorch_lightning.utilities.seed import seed_everything
+from pytorch_lightning.utilities.apply_func import apply_to_collection
 
 if _TPU_AVAILABLE:
     import torch_xla.core.xla_model as xm
@@ -37,6 +38,10 @@
 else:
     xm, xla_pl, xmp, ParallelLoader, rendezvous = [None] * 5
 
+if _OMEGACONF_AVAILABLE:
+    from omegaconf import OmegaConf
+    from omegaconf import DictConfig, ListConfig
+
 
 class TPUSpawnPlugin(DDPSpawnPlugin):
 
@@ -304,4 +309,6 @@ def save_checkpoint(self, checkpoint: Dict[str, Any], filepath: str) -> None:
             filepath: write-target file's path
         """
         # Todo: TypeError: 'mappingproxy' object does not support item assignment
+        if _OMEGACONF_AVAILABLE:
+            checkpoint = apply_to_collection(checkpoint, (DictConfig, ListConfig), OmegaConf.to_container)
         self.save({k: v for k, v in checkpoint.items() if k != "callbacks"}, filepath)