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

[Junio C Hamano <gitster@pobox.com>]

Johannes Schindelin <Johannes.Schindelin@gmx.de> writes:

>> 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".
>
> Given the substantial pain and suffering I have due to per-worktree
> reflogs (and those are *just* HEAD's reflogs!), it appears to me that
> per-worktree refs would be a particularly poor feature.
>
> I agree that HEAD needs to be per-worktree, but already the fact that the
> HEADs of the worktrees, along with their reflogs, are *not* visible to
> all other worktrees causes substantial trouble.

Not so fast; it cuts both ways.

People who want multiple worktrees with branches checked out to work
in would want to do per-worktree things like bisection, which needs
tons more state than we'd be comfortable having directly under
$GIT_DIR (e.g. they may also want "git merge" or "git pull", which
would use MERGE_HEAD and FETCH_HEAD that are per-worktree and not
under refs/; "git bisect" would want to mark number of commits to
denote the perimeter of the area of the history being bisected and
they live refs/bisect/).

And when you are bisecting in the worktree dedicated for a topic,
it is a feature that your other worktrees do not need to see how
much history you narrowed down in that topic.