tracking a tree that doesn't progress linearly

tracking a tree that doesn't progress linearly

[Paul Mackerras]

I want to be able to publish a git tree for others to follow but I
also want to be retain the freedom to remove commits and/or rebase
commits in the tree.  For example, if someone sends me a patch and I
put it in the tree, then they send me a revised version, I want to be
able to roll back to just before I applied the older patch and start
again from there.

What this means, AFAICS, is that the head of the published tree won't
always be a descendent of all previous values of the head.  If
somebody is following the state of the tree by doing a git pull every
so often, and I have rolled back the tree and applied some new
patches, then the git pull will try to merge the old and new state,
which is not what we want.  What we want is something that just gets
the local tree to the same state as the remote tree.

Is there a git command which does the equivalent of a git fetch,
followed by setting the head and checking it out?

Or is this an incredibly stupid idea for some reason that hasn't
occurred to me yet? :)

Thanks,
Paul.

Re: tracking a tree that doesn't progress linearly

[Martin Langhoff]

On 11/11/05, Paul Mackerras <paulus@samba.org> wrote:
> I want to be able to publish a git tree for others to follow but I
> also want to be retain the freedom to remove commits and/or rebase
> commits in the tree.

I sometimes want that too, but git doesn't have a 'rewind' semantics,
and probably for a good reason. The approach I am studying is to
create a thousand throaway short-lived branches. It is safe to publish
them as long as people following your branches _know_ that they'll be
orphaned, and that any commits they have on top of them they'll have
to rebase.

So you could publish your tree with devel-<datestamp> heads, and
announce when you're moving to a newer one. People tracking your
branches can tend register & checkout the new branches, and do a
git-merge to rebase their patches to your new branch, or replay them
with git-format-patch and git-am.

On the other hand, if  StGIT grows better support for sharing patches,
it could make all this look like the stone age.

cheers,


martin

Re: tracking a tree that doesn't progress linearly

[Catalin Marinas]

Paul Mackerras <paulus@samba.org> wrote:
> I want to be able to publish a git tree for others to follow but I
> also want to be retain the freedom to remove commits and/or rebase
> commits in the tree.  For example, if someone sends me a patch and I
> put it in the tree, then they send me a revised version, I want to be
> able to roll back to just before I applied the older patch and start
> again from there.

I'm facing a similar problem. I use StGIT for my development branch
(usually with less than 20 patches) but I would like to export a HEAD
for others to pull from. When rebasing the patches with StGIT, the new
HEAD wouldn't be a descendant of the old one.

The partial solution I got to was to make the master branch available
to people and the devel branch private. Initially, the master branch
would pick the patches ('stg pick') from the devel branch which I want
to make public. When I'm happy with the patches on the master branch,
I run 'stg commit' and store them permanently (you won't be able to
modify them). After permanently storing the patches, I can use the
master branch in the normal way with GIT (merge, pull, push etc.).

When I get a patch in the devel branch updated, I just run 'stg pick
patchname@devel' in the master branch. Because of the nature of the
three-way merge, the new picked patch should only contain the
differences from the previous one. It might also cause conflicts which
need resolving if the new patch modifies lines which were present in
the old patch (i.e. not only additions or removals). At this point you
can change the patch description since the new picked patch only
represents an update to the old one and not the full feature.

The only little drawback I see with this approach is that merging in
the latest changes from the mainline kernel could produce identical
conflicts (if any) in both master and devel branches.

-- 
Catalin

Re: tracking a tree that doesn't progress linearly

[Petr Baudis]

Dear diary, on Fri, Nov 11, 2005 at 04:18:31AM CET, I got a letter
where Paul Mackerras <paulus@samba.org> said that...
> I want to be able to publish a git tree for others to follow but I
> also want to be retain the freedom to remove commits and/or rebase
> commits in the tree.  For example, if someone sends me a patch and I
> put it in the tree, then they send me a revised version, I want to be
> able to roll back to just before I applied the older patch and start
> again from there.
> 
> What this means, AFAICS, is that the head of the published tree won't
> always be a descendent of all previous values of the head.  If
> somebody is following the state of the tree by doing a git pull every
> so often, and I have rolled back the tree and applied some new
> patches, then the git pull will try to merge the old and new state,
> which is not what we want.  What we want is something that just gets
> the local tree to the same state as the remote tree.
> 
> Is there a git command which does the equivalent of a git fetch,
> followed by setting the head and checking it out?

I plan to change the fast-forward condition in Cogito from

	is_ancestor(current, new_head)

to

	current == old_head || is_ancestor(current, new_head)

which should enable you to do this - just rebase, and it will Just Work
for those cg-update'ing from you; the only problem si that cg-fetch +
cg-merge will NOT work, but I have no simple workaround for that.

I already proposed this several times and it was always passed in
silence, so I assume there are no problems with this approach.

-- 
				Petr "Pasky" Baudis
Stuff: http://pasky.or.cz/
VI has two modes: the one in which it beeps and the one in which
it doesn't.