Add checkpoint parameter to on_save_checkpoint

[carmocca]

What does this PR do?

See title

class MyCallback(pl.Callback):
    def on_save_checkpoint(trainer, pl_module, checkpoint: ADDED):
       # the checkpoint parameter is the current checkpoint state. this function
       # should still return the callback state.
       ...

Necessary because the ModelPruning callback needs to modify the saved checkpoint model state. See #6073

Backwards compatibility

Inspect the target callback on_save_checkpoint signature and if it only has two arguments print a DeprecationWarning and call it without the checkpoint

Before submitting

• [n/a] 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

• 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

[pep8speaks]

Hello @carmocca! Thanks for updating this PR.

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

Comment last updated at 2021-02-24 13:21:47 UTC

[codecov]

Codecov Report

Merging #6072 (986eec2) into master (46617d9) will decrease coverage by 0%.
The diff coverage is 100%.

@@          Coverage Diff           @@
##           master   #6072   +/-   ##
======================================
- Coverage      93%     93%   -0%     
======================================
  Files         159     159           
  Lines       11375   11382    +7     
======================================
- Hits        10626   10604   -22     
- Misses        749     778   +29     

[rohitgr7]

are we allowed to update the existing hooks??
#6059 (comment)
#6059 (comment)

[carmocca]

are we allowed to update the existing hooks??

Why not? Especially if it's necessary for progress. We just have to be careful about backwards compatibility.

[SeanNaren]

are we allowed to update the existing hooks??
#6059 (comment)
#6059 (comment)

A last minute change to the API for the release, I didn't want to add too much additional logic especially to existing APIs. @carmocca suggested fix by inspection will work fine!

[rohitgr7]

are we allowed to update the existing hooks??
#6059 (comment)
#6059 (comment)

A last minute change to the API for the release, I didn't want to add too much additional logic especially to existing APIs. @carmocca suggested fix by inspection will work fine!

@SeanNaren so can we add it now, and of course, complete it with the correct dataloader_idx?

[tchaton]

LGTM !