Re: [PATCH] Add new @ shortcut for HEAD

[Felipe Contreras <felipe.contreras@gmail.com>]

On Tue, Apr 30, 2013 at 2:42 PM, Junio C Hamano <gitster@pobox.com> wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
>> 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.
>
> Let me change my mind once again ;-)
>
> As @ has been a valid character in a ref, I think "git show master@"
> and "git show HEAD@" _should_ error out, not because they suffix
> 'master' and 'HEAD" in a funny way, but simply because there is no
> branch called 'master@' (i.e. 'git for-each-ref | grep master@'
> yields empty).  After you run "git branch master@ master~26", you
> should see "git show master@" not to error out, because that is just
> the name of a branch with somewhat an unusual name.

There is also no branch named master@{0}. And there are no branches
with @{ in them, because we forbid them. So the question is what do we
want to forbid? If we don't want to forbid 'master@', then sure
'master@' should not evaluate to 'master'.

> And we can still have "git show @" to do "git show HEAD", based on a
> world model completely different from I (incorrectly) advocated in
> the message I am replying to.
>
> The rule would be "You should be able to say '@' where-ever you
> currently say HEAD" (aka '@' is a short-hand for 'HEAD').
>
> That means "git checout @" should work the same way as "git checkout
> HEAD", "git log @~4" would work the same way as "git log HEAD~4",
> "git update-ref @ $(git rev-parse master)" should update the HEAD
> without creating $GIT_DIR/@, etc.
>
> You can't go any simpler than that rule, and there is no room for
> confusion if that rule is properly implemented.

I disagree. I can do 'git log @{-1}-4', but I cannot do 'git
update-ref @{-1}'. Why? Because the '@' notation is for revision
parsing, and 'git update-ref' doesn't do revision parsing.

I'd say, everywhere where you could do @{-1}, you should be able to do @.

Cheers.

-- 
Felipe Contreras