Re: [PATCH] Add "list" and "rm" sub commands to tg-depend

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

Hello Bert,

On Sat, Apr 11, 2009 at 05:40:04PM +0200, Bert Wesarg wrote:
> 2009/4/9 Uwe Kleine-König <u.kleine-koenig@pengutronix.de>:
> > Hello,
> >
> > On Thu, Apr 09, 2009 at 08:01:04PM +0200, Bert Wesarg wrote:
> >> 2009/4/9 Ira Weiny <weiny2@llnl.gov>:
> >> > On Thu, 9 Apr 2009 14:43:37 +0200
> >> > Uwe Kleine-König <u.kleine-koenig@pengutronix.de> wrote:
> >> >> You might want to check
> >> >>
> >> >>       http:// thread.gmane.org/gmane.comp.version-control.git/114581
> >> >
> >> > Ah this brings up more issues I had not thought about...  :-(  But perhaps
> >> > Bert's work could be used to help implement "rm".  Thoughts?
> >> No, it wont help. Because the base and tip of the topic should not
> >> changed in respect to the old state (expect for .topdeps of course).
> >>
> >> If you really want to remove a dependency, you need to revert a merge
> >> of this dep from the topic base. which is not possible today, or maybe
> >> I have just an idea for this:
> >>
> >>   'topic': the topic
> >>   'base':  the base of the topic, i.e. a merge from all dependent
> >> topics dep0, ..., depN
> >>
> >> say you want to remove dep0
> >>
> >>   1) merge all deps dep1, ..,depN into 'new-base'
> >>
> >>   2) merge 'new-base' into base with the merge driver 'theirs', that
> >> would overwrite all changes from dep0 in the 'base'
> >>
> >>   3) update 'topic' to the updated 'base'
> >>
> >> Any thoughts from someone who knows more than me?
> > Some time ago I thought about a similar issue:
> >
> > I based a branch on top of the Linux tree of the ARM maintainer (in the
> > following called "rmk") and decided later to base it on top of Linus'
> > tree.  So I did ~:
> >
> >        git checkout refs/top-bases/$branch
> >        git merge -s theirs linus/master
> >        git checkout $branch
> >        sed -i s,rmk,linus, .topdeps
> >        git add -f .topdeps
> >        git commit -m $commitmsg
> >        tg update
> >
> > When I thought about it with pencil and paper back then, I saw a problem
> > with that approach.  Now I invested some time now to verify it really
> > exists:  In fact I reverted the changes in the rmk/master branch.
> > Consider Linus pulls from rmk and I update my topgit branch.  Guess what
> > happens?  Linus' pull + my revert yield Linus' tree without rmk's
> > changes.
> >
> > Here is my recipe:
> >
> >        # prepare linus/master
> >        git init
> >        echo 'VERSION=2.6.28' > Makefile
> >        git add Makefile; git commit -m 'v2.6.28'
> >        git branch -m master linus/master
> >
> >        # prepare rmk/master
> >        git checkout -b rmk/master
> >        echo 'support for some machine' > arm.c
> >        git add arm.c; git commit -m 'support for some machine'
> >
> >        # new topgit branch
> >        tg create t/test
> >        echo change > lib.c
> >        git add lib.c; git commit -m 'tralala'
> >
> >        # Linus goes on ...
> >        git checkout linus/master
> >        echo 'VERSION=2.6.29-rc1' > Makefile
> >        git add Makefile; git commit -m 'v2.6.29-rc1'
> >
> >        # "rebase" test branch on linus/master
> >        git checkout refs/top-bases/t/test
> >        git symbolic-ref HEAD refs/top-bases/t/test
> >        git merge --no-commit linus/master
> >        git read-tree linus/master
> >        git commit
> >        rm arm.c
> >        git checkout t/test
> >        sed -i s/rmk/linus/ .topdeps
> >        git add .topdeps; git commit -m 'change dep: rmk/master -> linus/master'
> >        tg update
> >
> >        # Linus pulls from rmk
> >        git checkout linus/master
> >        git merge rmk/master
> >
> >        # update test to linus+rmk
> >        git checkout t/test
> >        tg update
> >
> >        # inspect:
> >        git diff linus/master refs/top-bases/t/test
> >
> > The last command shows that refs/top-bases/t/test doesn't have arm.c
> > :-/
> >
> > I'm sure the dependency deletion has exactly the same problem.
I think I've a solution.  Not an implementation yet, but the right
thoughs (I hope):

tg should not merge using the full history but fake the collapsed (as in
tg export --collapse) history as HEAD.

> You're probably right. I just found the old discussion about
> dependencies removal [1]:
> 
> On zo, 2008-09-21 at 16:24 +0200, Petr Baudis wrote:
> > The problem is that you can undo the merge content, but not the history
> > information. So this revert can e.g. propagate even into branches which
> > still *should* depend on the other branch, you get into trouble when you
> > want to make your branch depend on the other one anyway, etc.
> 
> On di, 2008-09-23 at 15:27 +0200, Petr Baudis wrote:
> > what we can't make to work is just the
> > most generic case, but e.g. if master is a *leaf* branch nothing else
> > depends on and it can't get the branch through multiple paths, you can
> > do the dependency removal rather easily (if it can get through multiple
> > paths, you can still do it but you might have to deal with big
> > conflicts).
> 
> Maybe the leaf solution could be done.  Only directly depending
> branches from the transitive reduction should be removable.  This
> would help for the 'tip'/'current' branch usecase, for collecting
> topics.
> 
> Bert
> 
> [1] http://thread.gmane.org/gmane.comp.version-control.git/95458/focus=96093
This link isn't optimal.  The highlighted message doesn't contain the
citations above :-/.

Best regards
Uwe

-- 
Pengutronix e.K.                              | Uwe Kleine-König            |
Industrial Linux Solutions                    | http://www.pengutronix.de/  |