Pytorch-lightning: Split ModelCheckpoint filepath into dirpath and filename

[carmocca]

🚀 Feature

Previous discussions:

https://github.com/PyTorchLightning/pytorch-lightning/pull/3163#issuecomment-683539565
https://github.com/PyTorchLightning/pytorch-lightning/pull/3163#issuecomment-695854769
https://github.com/PyTorchLightning/pytorch-lightning/issues/3001

Idea:

Keep backwards compatibility by having filepath (old parameter) and dirpath, filename (new parameters)
- if filepath is set: old logic, show deprecated warning.
- if dirpath and filename are set: new logic.
- if filepath, dirpath, and filename are set: raise MisconfigurationException

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cc @Borda @awaelchli @ananthsub @rohitgr7 @ydcjeff

[rohitgr7]

I have been suggesting this for a long time. 😅

[carmocca]

I know, @Borda just asked me to create a new issue to discuss.

[Borda]

I have been suggesting this for a long time. 😅

but it was not properly resolved, right? do you remember the issue/PR?

[awaelchli]

I like it, I vote for this :) We have plenty of tests for the filepath arg (I think thanks to @carmocca?), so the guarantee for back compatibility is there.

[awaelchli]

but it was not properly resolved, right? do you remember the issue/PR?

There was this PR #2584 but was slightly different

[rohitgr7]

Should we have these parameters now in ModelCheckpoint since 1.x is released?

[awaelchli]

Yes, I think it would be useful.