Re: Keep reflogs for deleted (remote tracking) branches?

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

On Mon, Mar 14 2022, Tao Klerks wrote:

> On Tue, Mar 8, 2022 at 2:05 PM Ævar Arnfjörð Bjarmason <avarab@gmail.com> wrote:
>> More generally I have not really run into this as a practical
>> problem.
>
> That's fair, nor have I - but I *have* come reasonably close: one
> person accidentally deletes a branch that someone else had prepared
> *without even realizing*, and the initial author is not available, and
> I only find out about it a few hours later. Dangling commit hunt, here
> we come. (the original author became available and re-pushed before it
> came to that)

I think you might find it interesting to have pre-receive hooks
e.g. reject pushes if you're deleting a topic whose commits aren't
entirely <your author> i.e. just something like:

    git push -o ireallymeanit=1 --delete topic

I.e. it's an easy to implement extra safety check that people can always
opt-out of, print a scary message and most people will think twice :)

>> Another way to solve a similar problem is to have
>> pre-receive/post-receive hooks log attempted/successful pushes, which
>> along with an appropriate "gc" policy will allow you to manually look up
>> these older branches (or even to fetch them, if you publish the log and
>> set uploadpack.allowAnySHA1InWant=true).
>
> Yep, that's closer to my expected plan, thanks - my intent is to back
> up, on force-push and/or deletion, into a specific refspace with a
> cleanup policy, using a server hook. So after something is "deleted"
> (or force-pushed away), it can be easily recovered for a period of eg
> 3 months in that refspace, eg
> "refs/force-push-backups/YYYY-MM-DD-<BRANCHNAME>-<HASHPREFIX>".
>
> My question is specifically about the, in my opinion, very surprising
> behavior of deleting reflogs along with deleted branches - I mainly
> provided the example use-case for context.

Yes it's quite a mess, e.g. if you follow the rabit hole at the
recent[1].

One fundimental problem (discussed in various places around the reftable
backend) is that we carry N meanings for an empty reflog:

A. "This is an active branch, but we have expired the entries".

B. "I manually created this, knowing that the various core.* configs
   around reflog will say "oh, a reflog exists, let's log to it" (in
   some cases).

C. Another is: This is "stale" log, i.e. no branch exists, but the log
   is there.

Which is one reason[2] we'd delete them on branch deletion, because
otherwise we'd start logging again when a branch is re-created, which
possibly isn't what we wanted.

1. https://lore.kernel.org/git/de5e2b0e290791d0a4f58a893d8571b5fc8c4f1a.1646952843.git.avarab@gmail.com
2. I'm not saying this was intended, and haven't looked into this case,
   just that's it it's an emergent effect of how these files are treated
   now.