Re: [PATCH] refs: allow @{n} to work with n-sized reflog

[Denton Liu <liu.denton@gmail.com>]

On Fri, Jan 01, 2021 at 05:36:06PM -0800, Denton Liu wrote:
> This sequence works
> 
> 	$ git checkout -b newbranch
> 	$ git commit --allow-empty -m one
> 	$ git show -s newbranch@{1}
> 
> and shows the state that was immediately after the newbranch was
> created.
> 
> But then if you do
> 
> 	$ git reflog expire --expire=now refs/heads/newbranch
> 	$ git commit --allow=empty -m two
> 	$ git show -s newbranch@{1}
> 
> you'd be scolded with
> 
> 	fatal: log for 'newbranch' only has 1 entries
> 
> While it is true that it has only 1 entry, we have enough
> information in that single entry that records the transition between
> the state in which the tip of the branch was pointing at commit
> 'one' to the new commit 'two' built on it, so we should be able to
> answer "what object newbranch was pointing at?". But we refuse to
> do so.
> 
> Make @{0} the special case where we use the new side to look up that
> entry. Otherwise, look up @{n} using the old side of the (n-1)th entry
> of the reflog.
> 
> Suggested-by: Junio C Hamano <gitster@pobox.com>
> Signed-off-by: Denton Liu <liu.denton@gmail.com>

I forgot to mention that the original thread that spawned this idea is
here:

	https://lore.kernel.org/git/xmqqzh8zgcfp.fsf@gitster.c.googlers.com/