Re: git rebase command and docs questions

Sverre Rabbelier [off-list ref] writes:

On Fri, Apr 9, 2010 at 20:49, Eugene Sajine [off-list ref] wrote:

quoted

But, in “git rebase –onto master next topic” the meaning of the “next
topic” parameters is different: as I understand, it actually specifies
a range of commits from next to topic,  because –onto changes the way
the whole command is working, but it is not clarified in help. Is that
correct understanding?

I've never been able to remember how rebase --onto works, perhaps if
we actually let users specify a range it would be more intuitive?

$ git rebase next..topic master

Hmm, re*base* means "change the base to _this one_"; the above is more
like "replay these on master", which is often a useful operation but is
different.

Suppose other people have worked on the project and made their pushes
since you started working on your changes:

      o---o master
     /
 ---o---o---o---o origin

"git rebase origin" asks "I know my current work is based on a tad stale
state, and I'd prefer a linear history, so change the base to origin".

If the thing of whose base you want to change is not your "current work",
then you name that explicitly, i.e. "git rebase origin master" (i.e. the
second branch name defaults to HEAD as usual).

Onto is an optional feature that is primarily for correcting your earlier
mistakes.  Notice in the above picture, other people doing parallel work
and pushing their changes out is part of the normal life of distributed
development; there is no mistake on your part involved.

But suppose you started building bugfixes in a topic forked from origin,
but after that you realize they should be based on origin/maint:

                   X---Y fixes
                  /
         o---o---o---o---o origin
        /
    ---o---o---o origin/maint

You could have made fixes branch that houses X and Y on origin/maint (and
later merge that to master to be pushed to origin), but you did not have
perfect foresight.  You do not obviously want to change the base of whole
'fixes' branch to 'origin/maint', as that will pull in changes in origin
that are not related to your fixes.

You would want to rebase 'fixes' branch (whose fork point can be specified
with 'origin') but not on top of 'origin', but on 'origin/maint'.  Hence
instead of running "git rebase origin" to produce

                           X'--Y' fixes
                          /
         o---o---o---o---o origin
        /
    ---o---o---o origin/maint

You would say "git rebase --onto origin/maint origin" to transplant X' and
Y' as if you started working from 'origin/maint':


         o---o---o---o---o origin
        /
    ---o---o---o origin/maint
                \
                 X'--Y' fixes

If you _had_ your "replay" command, the workflow for this would be:

    $ git checkout -b maint-fixes origin/maint
    $ git replay origin..fixes


Before somebody else makes useless noises, "cherry-pick" could be a good
command in the existing UI set to do that kind of thing.