* Raise an error when lightning replaces an existing sampler
Currently, Trainer replaces the existing sampler with DistributedSampler
if running distributing training and `replace_sampler_ddp=True` (default
behaviour). If a user has configured an existing sampler, this would
lead to widely different results if running a distributed vs
non-distributed training.
This PR fixes this by raising an Error if user has configured a sampler
and uses `replace_sampler_ddp=True`. The recommended behavior from now
on is to either remove the sampler or set `replace_sampler_ddp=False`
* Fix tests
* Simpler fix
* Fix tests
* Make inner method protected
* Apply suggestions from code review
Co-authored-by: Jirka Borovec <Borda@users.noreply.github.com>
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* replace ddp spawn with subprocess
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
* hot fix
