From: Junio C Hamano <gitster@pobox.com>
Date: Thu, 17 Dec 2020 19:49:21 GMT
Subject: Re: [PATCH] worktree: teach `repair` to fix multi-directional breakage
Message-ID: <xmqqwnxgxlfi.fsf@gitster.c.googlers.com>
In-Reply-To: <CAPig+cQT2Cj4i=2kq_svMyKiFmNLxvpa5kG=XNeaT+8UD5238Q@mail.gmail.com>

Eric Sunshine <sunshine@sunshineco.com> writes:

> We only have the paths making the two-way link between the repository
> and the secondary worktrees. Specifically, the outgoing
> <repo>/worktrees/<id>/gitdir points at /path/to/worktree/.git, and the
> incoming /path/to/worktree/.git points at <repo>/worktrees/<id>.

Yes.

> The inference is intentionally simple-minded. There is no path-based
> inference or other heuristic at play; the entire inference is based
> upon <id>. The worktree's path is specified as an argument. `git
> worktree repair` manually reads the ".git" gitfile at that location
> and, if it is well-formed, extracts the <id>. It then searches for a
> corresponding <id> in <repo>/worktrees/ and,...

That is exactly the point I got confused.  The worktree's path comes
as an argument from the user, so we'd trust it.  And it has ".git"
that is a gitfile that used to point at <repo> but because we are
trying to deal with a situation where both worktree and repo moved,
it cannot be used to learn where <repo> is.  Then, even after
learning what <id> to use, how would we know where to use that <id>
to find <repo>/worktrees/<id>, when the location of <repo> is unknown?

I think the answer is "where the user starts the 'git worktree'
command has to be under control of some repository (perhaps found by
a call to setup_git_directory()), and we'd use that one as <repo>".

Since I did not see that (in hindsight an obvious) piece, I failed
to see how it could possibly work.  But now it is clear.

Thanks.