Re: [PATCH] Add new @ shortcut for HEAD

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

Duy Nguyen <pclouds@gmail.com> writes:

> On Tue, Apr 30, 2013 at 2:35 AM, Felipe Contreras
> <felipe.contreras@gmail.com> wrote:
>> So we can type '@' instead of 'HEAD@', or rather 'HEAD'. So now we can
>> use 'git show @~1', and all that goody goodness.
>
> I like this. I haven't spent a lot of time on thinking about
> ambiguation. But I think we're safe there. '@' is not overloaded much
> like ':', '^' or '~'.
>
>> This patch allows 'HEAD@' to be the same as 'HEAD@{0}', and similarly with
>> 'master@'.
>
> I'm a bit reluctant to this. It looks like incomplete syntax to me as
> '@' has always been followed by '{'. Can we have the lone '@' candy
> but reject master@ and HEAD@? There's no actual gain in writing
> master@ vs master@{0}.

Originally I was going to say the same, but after thinking about it
a bit more, I changed my mind.

If you accept only "@" but not "master@", that behaviour needs a
wrong world model to understand and justify (one of which is "@ is a
synonym for HEAD").  If your rule is "In $anything@{$n}, you can
drop {$n} when $n==0", then HEAD@{0} becomes HEAD@ and master@{0}
becomes master@, and @{0} becomes @ naturally.

We should make sure that the code rejects "git update-ref @ foo"
because that is "git update-ref @{0} ref", by the way.  I didn't
check with Felipe's patch.

>> +'@'::
>> +  '@' alone is a shortcut for 'HEAD'
>> +

I think this explanation sends a wrong message, hinting as if you
can expect "update-ref @ master", "symbolic-ref @ refs/heads/next"
etc. to do something sensible to HEAD.

Felipe's original justification in the log message "I want to drop
{0}" sounds closer to what is going on here.