Re: "git merge" merges too much!

[Dmitry Potapov <dpotapov@gmail.com>]

On Tue, Dec 01, 2009 at 04:58:34PM -0500, Greg A. Woods wrote:
> At Tue, 1 Dec 2009 23:50:57 +0300, Dmitry Potapov <dpotapov@gmail.com> wrote:
> Subject: Re: "git merge" merges too much!
> > 
> > > > 
> > > > $ git branch new-foo foo
> > > > 
> > > > $ git rebase --onto newbase oldbase new-foo
> > > 
> > > Hmmm.... I'll have to think about that.  It makes some sense, but I
> > > don't intuitively read the command-line parameters well enough to
> > > predict the outcome in all of the scenarios I'm interested in.
> > > 
> > > what is "oldbase" there?  I'm guessing it means "base of foo" (and for
> > > the moment, "new-foo" too)?
> > 
> > You have:
> > 
> >  o---o---o---o---o  newbase
> >        \
> >         o---o---o---o---o  oldbase
> >                          \
> >                           o---o---o  foo
> 
> Yes, sort of -- in the ideal situation, but not in my particular example
> where "oldbase" is just a tag, not a real branch.

It does not matter whether it is tag or branch or just SHA-1. You can
use any two reference as newbase and oldbase. They specify two points
in DAG. The only thing that has to be a branch in my example is new-foo.

> 
> So yes, "oldbase" is in fact "base of foo".  Trickier still is when the
> "oldbase" branch has one or more commits newer then "base of foo".  Does
> Git not have a symbolic name for the true base of a branch?  I.e. is
> there not some form of symbolic name for "N" in the following?
> 
>    o---o---o---o---o---o---o---o  master
>             \
>              o---o---N---o---o  release-1
>                       \
>                        o---o---o  local-release-1

You can always find SHA-1 for N using the following command:

  git merge-base release-1 local-release-1

but you do not have to do that to rebase your changes. You just can run:

   # create a copy of local-release-1, so it will not disappear
   git branch copy-release-1 local-release-1

   # rebase the branch to master
   git rebase --onto master release-1 copy-release-1


Dmitry