From: Junio C Hamano <junkio@cox.net>
Date: Wed, 09 May 2007 19:37:11 GMT
Subject: Re: [PATCH] checkout: allow full refnames for local branches
Message-ID: <7v8xbxu6u0.fsf@assigned-by-dhcp.cox.net>
In-Reply-To: <8c5c35580705090207y2979aaa5u7ce9de5fa1dfe658@mail.gmail.com>

"Lars Hjemli" <hjemli@gmail.com> writes:

> On 5/9/07, Junio C Hamano <junkio@cox.net> wrote:
>> Lars Hjemli <hjemli@gmail.com> writes:
>>
>> > This teaches git-checkout to strip the prefix 'refs/heads/' from the
>> > supplied <branch> argument
>>
>> Why is this necessary, may I ask?
>>
>
> I'm playing around with a gui frontend, and there I use
> git-for-each-ref to obtain possible arguments for git-checkout. That's
> how I discovered the 'problem', and solved it by stripping
> 'refs/heads/' in my frontend.

Pathspec-less variant of "git checkout" takes two kinds of
parameters and has two flavours in its behaviour:

 (1) an exact branch name, in which case it switches to the
     branch; otherwise

 (2) any arbitrary commit object name, in whch case it checks
     out and detaches HEAD.

A tricky part is that an exact branch name is often a perfectly
valid commit object name, so rule (1) trumps the rule (2).  You
just discovered a way to have a detached HEAD at a commit that
happens to be at an existing branch -- by naming that commit
without using its exact branch name.

An easier way to spell that would be:

	$ git checkout master^0

but

	master^0
        heads/master
        refs/heads/master

are all perfectly good ways to talk about the commit at the tip
of the 'master' branch without spelling it as an exact
branch name (which is 'master').