Re: [PATCH 15/15] builtin/gc: pack refs when using `git maintenance run --auto`

> When running `git maintenance run --auto`, then the various subtasks
> will only run as needed. Thus, we for example end up only packing loose
> objects if we hit a certain threshold.
>
> Interestingly enough, the "pack-refs" task is actually _never_ executed
> when the auto-flag is set because it does not have a condition at all.
> As 41abfe15d9 (maintenance: add pack-refs task, 2021-02-09) mentions:
>
>     The 'auto_condition' function pointer is left NULL for now. We could
>     extend this in the future to have a condition check if pack-refs
>     should be run during 'git maintenance run --auto'.
>

> It is not quite clear from that quote whether it is actually intended
> that the task doesn't run at all in this mode. Also, no test was added
> to verify this behaviour. Ultimately though, it feels quite surprising
> that `git maintenance run --auto --task=pack-refs` would quietly never
> do anything at all.
>
> In any case, now that we do have the logic in place to let ref backends
> decide whether or not to repack refs, it does make sense to wire it up
> accordingly. With the "reftable" backend we will thus now perform
> auto-compaction, which optimizes the refdb as needed.
>
> But for the "files" backend we now unconditionally pack refs as it does
> not yet know to handle the "auto" flag. Arguably, this can be seen as a
> bug fix given that previously the task never did anything at all.
> Eventually though we should amend the "files" backend to use some
> heuristics for auto compaction, as well.
>