From: Michael Haggerty <mhagger@alum.mit.edu>
Date: Tue, 31 Jan 2012 08:57:17 GMT
Subject: Re: Bug: "git checkout -b" should be allowed in empty repo
Message-ID: <4F27ACED.2050709@alum.mit.edu>
In-Reply-To: <7v39axc9gp.fsf@alter.siamese.dyndns.org>

On 01/30/2012 07:48 PM, Junio C Hamano wrote:
> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
>> [3] If commit 0000000 were treated specially, then there would be no
>> unborn branches but only branches pointing at the empty commit.  In that
>> case, my expectation would change--the old branch should be left
>> pointing at 0000000.  But currently git has no concept of an unborn
>> branch that is not HEAD.
> 
> And it probably is not a good thing to add such. Under that constraints,
> HEAD that says refs/heads/foo where foo does not exist yet needs to be
> special cased at places where it matters.
> 
> For that matter, even if we artificially created refs/heads/foo before any
> commit is made and made it point at 0{40}, you would need to add special
> cases to other parts of the system

No, the idea is to avoid special casing by making 0{40} into a real (but
empty) revision.

> (e.g. "commit" needs to notice that the
> result should be a root, not a child of 0{40};

No, commits that were previously generated as orphans *would* now be
generated as children of the special 0{40} commit.

> "checkout other_branch"
> needs to notice that it should refrain from running the equivalent of
> "read-tree -m HEAD other_branch" because HEAD does not point at a real
> tree;

No, it would merge the 0{40} commit with other_branch like usual,
resulting in the same contents as other_branch.  Indeed, if other_branch
is also ultimately a descendant of 0{40}, this would be like a
fast-forward merge.

> etc.

This "etc" might include problems.

> so it does not change the fact that the unborn branch is case
> is special.

On the contrary, I believe that much special casing could be eliminated
and the UI made more uniform by treating everything as a descendant of a
special "NULL" commit.

Michael

-- 
Michael Haggerty
mhagger@alum.mit.edu
http://softwareswirl.blogspot.com/