RE: How to update a cloned git repository

> From: Matthieu Moy [mailto:Matthieu.Moy@grenoble-inp.fr]
> Sent: Tuesday, September 11, 2012 1:06 PM
> To: Joachim Schmitz
> Cc: git@vger.kernel.org
> Subject: Re: How to update a cloned git repository
> 
> "Joachim Schmitz" <jojo@schmitz-digital.de> writes:
> 
> > Hi folks
> >
> > Probably a beginner's question...
> >
> > If I did a
> >    git clone git://guthub.com/git/git.git
> > and worked on some own branches of pu
> >    git checkout pu;git checkout -p mybranch;
> 
> I guess you meant "git checkout -b mybranch" (not -p).

> > hack;hack;...;git commit -a -s
> >
> > how to update my repository once the the one on github changed? A
> > plain git pull or git fetch;git merge keeps failing on my with lots of
> > conflicts, none of which relate to any of the changes I did (and hence
> > wouldn't know how to resolve)
> 
> Short answer: don't work on pu. Work on master unless you have a good
> reason not to.

> Longer answer: the pu branch in git.git is often re-written, hence the
> commit on which you started hacking once existed in git.git's pu, but it
> probably no longer is.
> 
> You cloned this:
> 
> --A---B---C <-- origin/pu
> 
> Hacked to this
> 
>          origin/pu
>           |
>           v
> --A---B---C---D---E <-- mybranch
> 
> and the next fetch resulted in something like this:
> 
>     B'---C'---D'---F <-- origin/pu
>    /
> --A---B---C---D---E <-- mybranch
> 
> while you could have expected that if origin/pu had just been
> fast-forwarded with a new commit F:
> 
>             F <-- origin/pu
>            /
> --A---B---C---D---E <-- mybranch
> 
> As a result, "git merge" computes a common ancestor very far backward in
> history. Instead of merging only your changes with new pu content, it
> merges the old history of pu (plus your changes) with the new history of
> pu, and you get spurious conflicts.
> 
> The solution is to rebase your changes (and only yours). My advice is to
> rebase them on master, like this (replace 42 by the number of commits
> you want to rebase in HEAD~42):
> 
>   git rebase HEAD~42 --onto origin/master