exp: stop checking for unchanged experiments

[dberenbaum]

Following up on iterative/dvc.org#4200 (comment):

Or, if nothing
has changed in the workspace, force saving an experiment anyway (identical to
Git HEAD).

@dtrifiro I missed this check in #8690. I don't think --force should be needed and it complicates this option. Can we drop it?

Ideally, we want to make dvc exp run the same and not worry about creating duplicate experiments (see the discussion in #8659 (comment)).

[codecov]

Codecov Report

Base: 93.52% // Head: 93.53% // Increases project coverage by +0.00% 🎉

Coverage data is based on head (dd3a7af) compared to base (4b0fa4d).
Patch coverage: 100.00% of modified lines in pull request are covered.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #8743   +/-   ##
=======================================
  Coverage   93.52%   93.53%           
=======================================
  Files         457      457           
  Lines       36282    36268   -14     
  Branches     5262     5258    -4     
=======================================
- Hits        33933    33923   -10     
+ Misses       1843     1838    -5     
- Partials      506      507    +1     

Impacted Files	Coverage Δ
dvc/repo/experiments/exceptions.py	79.62% <ø> (-1.41%)	⬇️
dvc/repo/experiments/__init__.py	87.68% <100.00%> (-0.41%)	⬇️
dvc/repo/experiments/executor/base.py	83.47% <100.00%> (+0.70%)	⬆️
dvc/repo/experiments/save.py	94.59% <100.00%> (-0.28%)	⬇️
tests/func/experiments/test_checkpoints.py	100.00% <100.00%> (ø)
tests/func/experiments/test_experiments.py	99.74% <100.00%> (+<0.01%)	⬆️
tests/func/experiments/test_save.py	100.00% <100.00%> (ø)
tests/func/experiments/test_show.py	99.40% <100.00%> (+0.59%)	⬆️
dvc/repo/experiments/queue/celery.py	86.19% <0.00%> (-1.87%)	⬇️
dvc/repo/experiments/queue/workspace.py	81.39% <0.00%> (-0.78%)	⬇️
... and 3 more

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[dberenbaum]

Need to fix tests

[dberenbaum]

One consequence of this is that there will often be an extra commit for checkpoints experiments. Before this PR, if I run a checkpoints experiment, DVC will create an additional commit at the end of the experiment only if there is a change from the last checkpoint. After this PR, DVC will always create an additional commit at the end of the experiment. I don't see this as a problem -- we are trading off some additional noise and duplication for a simpler approach that's more consistent and transparent.

cc @pmrowla @daavoo

[dberenbaum]

This PR also drops reset-specific logic when checking for conflicts. This is no longer needed since we randomly assign a new experiment name at each reset instead of overwriting the previous experiment. This partially addresses #8742.

[dberenbaum]

@pmrowla It looks like empty commits are generated for the final state of checkpoints with this PR. The experiment rows are identical and the git diff is empty.

$ dvc exp show
 ──────────────────────────────────────────────────────────────────────────────────────>
  Experiment                 Created        train.loss   train.acc   test.loss   test.a>
 ──────────────────────────────────────────────────────────────────────────────────────>
  workspace                  -                 0.67347     0.78732     0.66219     0.79>
  main                       Dec 15, 2022       0.9731      0.7694     0.95962     0.77>
  │ ╓ cfa235e [alive-bias]   12:03 PM          0.67347     0.78732     0.66219     0.79>
  │ ╟ a52327a                12:03 PM          0.67347     0.78732     0.66219     0.79>
  │ ╟ 952884b                12:03 PM          0.66759     0.79247     0.66191     0.78>
  │ ╟ d028ae0                12:03 PM          0.70363     0.78107     0.69235     0.78>
...
$ git diff cfa235e a52327a

[pmrowla]

@pmrowla It looks like empty commits are generated for the final state of checkpoints with this PR. The experiment rows are identical and the git diff is empty.

I think we can just open a separate issue for this and fix it in a follow up PR if needed (not sure it needs to be prioritized right away).