Re: gc and repack ignore .git/*HEAD when checking reachability

[Duy Nguyen <pclouds@gmail.com>]

On Sun, Jul 10, 2016 at 12:59 PM, Johannes Schindelin
<Johannes.Schindelin@gmx.de> wrote:
>> >> Now, how about special-casing *just* these legacy files in gc: HEAD,
>> >> FETCH_HEAD, MERGE_HEAD and CHERRY_PICK_HEAD? Any new transient refs should
>> >> live in the refs/ namespace, which is already handled.
>> >
>> > That seems workable as well; in that case, we should also document this
>> > (in the git-gc manpage at a minimum), and explicitly suggest creating
>> > refs in refs/ but outside of refs/heads/ and refs/tags/, rather than
>> > directly in .git/.
>>
>> Not just outside refs/heads and refs/tags. It has to be in a specified
>> namespace like refs/worktree/ or something (we are close to be ready
>> for that). We could update the man page about git-gc shortcomings now,
>> but I think we should wait until refs/worktree (or something like
>> that) becomes true before suggesting more.
>
> We have a precedent for a ref that is directly underneath refs/:
> refs/stash.
>
> IMO that is okay: depending on the use case, we would need multiple refs
> (like refs/notes/*) or a single ref (like refs/stash).
>
> The important part is that the new refs start with refs/, and if they are
> to be transient, start neither with refs/heads/ nor with refs/tags/.

No, the point is, refs subsystem needs to know which refs is per-repo,
which is per-worktree. So far the rules are  "everything under refs,
except a few known exceptions, is per-repo" and "everything directly
under $GIT_DIR is per-worktree", which work fine. But if you allow to
move per-worktree to "refs" freely, then the "known exceptions" will
have to be updated every time a new per-worktree ref appears. It'll be
easier to modify the first rule as "everything under refs, except some
legacy exceptions and refs/worktree, is per-repo".
-- 
Duy