allow to fail atime job in GHCI / use merge commits to allow branch deletion

[jangorecki]

You can try using the continue-on-error directive at the job level. Maybe base it off labels (then apply that label to this PR) since using pull_request.number would be redundant; e.g. say we name the label 'ignore-atime-failure':

continue-on-error: ${{ contains(github.event.pull_request.labels.*.name, 'ignore-atime-failure') }}

Originally posted by @Anirban166 in #7361 (comment)

[tdhock]

I'm not sure this is a good idea.
If the atime job is failing there is probably a reason that needs fixing. for example I see this PR https://github.com/Rdatatable/data.table/actions/runs/18464808691/job/52604142621?pr=7361 has atime error below,

Error in value[[3L]](cond) : 
  Error in revparse_single(object, branch): Error in 'git2r_revparse_single': Requested object could not be found

 when trying to checkout ffe431fbc1fe2d52ed9499f78e7e16eae4d71a93
Calls: <Anonymous> ... tryCatch -> tryCatchList -> tryCatchOne -> <Anonymous>
Timing stopped at: 16.42 3.21 17.99
Execution halted

this means that somebody deleted a branch with a commit required in an atime test.
Searching for "ffe43" in https://github.com/Rdatatable/data.table/blob/master/.ci/atime/tests.R#L47 shows this line

  Fast = "ffe431fbc1fe2d52ed9499f78e7e16eae4d71a93" # Last commit of the PR (https://github.com/Rdatatable/data.table/pull/4386/commits) where the performance was improved.

which has a reference to the PR #4386 that had the deleted branch. The fix which I just did was going to that PR page and clicking "Restore branch" button at the bottom.

[jangorecki]

That's a fair point, how should we know if a branch is safe to delete?

[MichaelChirico]

I have been trying to use the atime label to mark branches as required for the GHA

[jangorecki]

Ok, does that mean we should keep those branches forever? This feels suboptimal. I know many users who do git fetch origin rather than specific branch and it pollutes their git checkout experience... That why I cleaned up old merged branches recently.

[tdhock]

yes with the current setup we have to keep old branches with atime commits forever.

[MichaelChirico]

I agree it would be better but I think the benefit of {atime} outweighs this cost for now. Open to ideas for how else to make it work.

[jangorecki]

Instead of pointing to a commit from a branch atime could point to a merge commit. That will be always available in master.
That seems to be the optimal way.

Alternatively we could have a fork that keeps all branches needed for atime.

[tdhock]

using merge commits sounds like a good idea to me.

[MichaelChirico]

My memory is that doesn't work somehow, but I could be wrong, please test it out.