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

[Duy Nguyen <pclouds@gmail.com>]

On Tue, Jul 12, 2016 at 5:51 PM, Jeff King <peff@peff.net> wrote:
> On Tue, Jul 12, 2016 at 05:46:12PM +0200, Duy Nguyen wrote:
>
>> I'm not opposed to letting one worktree see everything, but this move
>> makes it harder to write new scripts (or new builtin commands, even)
>> that works with both single and multiple worktrees because you refer
>> to one ref (in current worktree perspective) differently. If we kill
>> of the main worktree (i.e. git init always creates a linked worktree)
>> then it's less of a problem, but still a nuisance to write
>> refs/worktree/$CURRENT/<something> everywhere.
>
> True. I gave a suggestion for the reading side, but the writing side
> would still remain tedious.
>
> I wonder if, in a worktree, we could simply convert requests to read or
> write names that do not begin with "refs/" as "refs/worktree/$CURRENT/"?
> That makes it a read/write-time alias conversion, but the actual storage
> is just vanilla (so the ref storage doesn't need to care, and
> reachability just works).

A conversion like that is already happening, but it works at
git_path() level instead and maps anything outside refs/ to
worktrees/$CURRENT. Reorganizing all refs in a single ref storage is
probably possible, but...

> The trickiest thing, I think, is FETCH_HEAD, which is not really a
> ref (because it may have a bunch of values, and contain extra
> information).

Yeah.. I think David and Junio touched this when lmdb backend was
discussed, which resulted in leaving per-worktree refs to filesystem
backend even when shared refs are in lmdb. We probably can still make
it work, I think refs subsystem has special case for FETCH_HEAD
already. But 'refs' stuff is really not my area, I should stop writing
now before making too many wrong statements.
-- 
Duy