[warning] Add a warning with missing callback with resume_from_checkpoint

[tchaton]

What does this PR do?

Add a warning with missing callback with resume_from_checkpoint

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

Anyone in the community is free to review the PR once the tests have passed.
Before you start reviewing make sure you have read Review guidelines. In short, see the following bullet-list:

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

Did you have fun?

Make sure you had fun coding 🙃

[pep8speaks]

Hello @tchaton! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-04-29 12:13:09 UTC

[codecov]

Codecov Report

Merging #7254 (5d91654) into master (e272bea) will increase coverage by 4%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #7254    +/-   ##
=======================================
+ Coverage      87%     91%    +4%     
=======================================
  Files         199     199            
  Lines       12799   12802     +3     
=======================================
+ Hits        11170   11683   +513     
+ Misses       1629    1119   -510     

[awaelchli]

Suggested change

	"Be aware that when using ``resume_from_checkpoint``, "
	"callbacks used to create the checkpoint need to be provided. "
	f"Please, add the following callbacks: {list(difference)}. ", UserWarning
	"Be aware that when using ``resume_from_checkpoint``,"
	" callbacks used to create the checkpoint need to be provided."
	f" Please add the following callbacks: {list(difference)}. ", UserWarning

[ananthsub]

is this warning always needed? For example, i may have saved a checkpoint dict which contained callback states from the model checkpoint. But when I resume from checkpoint, I might not set a new model checkpoint callback on the trainer

is there an issue/question which prompted the PR?

[tchaton]

This PR checks the AU~B between save_callback_state and current_callback_state.
Basically, if you trained with a CustomCallback and you don't provide it back when resuming,
we won't be able to reload the state as this callback isn't provided.
Therefore we should provide a warning that resume might not have the expected behaviour.

[tchaton]

resume_from_checkpoint is bringing lot of confusion as we expect exactly the same arguments to the Trainer as provided when training before.

[ethanwharris]

LGTM 😃 maybe just do set(callback_states.keys()) for readability