Re: [FIXED PATCH] Make rebase save ORIG_HEAD if changing current branch

On Jul 7, 2008, at 7:42 AM, Jakub Narebski wrote:

Theodore Tso [off-list ref] writes:

quoted

True, but (and please correct me if I'm wrong) ORIG_HEAD will always
be pointing out HEAD before the user typed pretty much any git
porcelein command (which saves HEAD into ORIG_HEAD), but with  
reflogs,
it you have to paw through multiple HEAD@{n} to find the 'n' which
corresponds to state before executing the git plumbing command, since
multiple git plumbing commands could have updated the HEAD's reflog,
right?

You can always use _branch_ reflog, either in the <branch>@{1} form,
or in @{1} shortcut form.  @{1} should be equovalent to ORIG_HEAD
even for rebase.

I personally expected @{1} to be identical to HEAD@{1}.  Since  
omitting a ref usually refers to HEAD, why shouldn't omitting it when  
referring to the reflogs mean the HEAD log?  The definition of @{1} is  
useful since there's no other easy way to get "current branch's  
reflog", but I think it's non-obvious.  (Since HEAD@{1} is something  
completely different, I think the only other way to refer to @{1} is $ 
(git symbolic-ref)@{1}.)

Also, your statement is only true if ORIG_HEAD was on the branch you  
are currently working.  If we want ORIG_HEAD to mean "state of HEAD  
before last command", then "git rebase upstream topic" from master  
should leave ORIG_HEAD pointing to master, not topic@{1}.  It also is  
no longer true if you switch branches.  Having ORIG_HEAD set to the  
point before a pull is useful to compare multiple branches to both the  
old and new position of your updated branch.

If we're going to have ORIG_HEAD set by _any_ command, we should  
probably come up with some consistent definition of it and set it  
appropriately.  The first place most people encounter ORIG_HEAD is  
after a pull, where it acts something like a reverse of FETCH_HEAD  
(old state of local vs. new state of remote).  However, pull only sets  
ORIG_HEAD by way of merge and reset sets ORIG_HEAD as well.  So the  
current definition appears to be "the prior state of the last branch  
to be drastically changed."  By this definition, ORIG_HEAD should be  
set by am and rebase as per Junio's patch.

You could make an argument for removing ORIG_HEAD, it's functionality  
being replaced by the reflogs.  At this point, it's a rather  
established bit of git, and I think has usefulness of it's own.

~~ Brian