Fix torchelastic detection with non-distributed installations (#13142)

* Fix torchelastic detection under Mac

* CHANGELOG

Author: carmocca

CHANGELOG.md

@@ -18,6 +18,7 @@ The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/).
 - Fixed the number of references of `LightningModule` so it can be deleted ([#12897](https://github.com/PyTorchLightning/pytorch-lightning/pull/12897))
 - Fixed `materialize_module` setting a module's child recursively ([#12870](https://github.com/PyTorchLightning/pytorch-lightning/pull/12870))
 - Fixed issue where the CLI could not pass a `Profiler` to the `Trainer` ([#13084](https://github.com/PyTorchLightning/pytorch-lightning/pull/13084))
+- Fixed torchelastic detection with non-distributed installations ([#13142](https://github.com/PyTorchLightning/pytorch-lightning/pull/13142))
 
 
 ## [1.6.3] - 2022-05-03

pytorch_lightning/plugins/environments/torchelastic_environment.py

@@ -62,7 +62,8 @@ def main_port(self) -> int:
     def detect() -> bool:
         """Returns ``True`` if the current process was launched using the torchelastic command."""
         if _TORCH_GREATER_EQUAL_1_9_1:
-            return torch.distributed.is_torchelastic_launched()
+            # if not available (for example on MacOS), `is_torchelastic_launched` is not defined
+            return torch.distributed.is_available() and torch.distributed.is_torchelastic_launched()
         required_env_vars = {"RANK", "GROUP_RANK", "LOCAL_RANK", "LOCAL_WORLD_SIZE"}
         return required_env_vars.issubset(os.environ.keys())