llvm dev - Feb 2011 - [LLVMdev] Official git mirroring of llvm, clang, lldb, test-suite, etc.?

Óscar Fuentes <ofv at wanadoo.es> writes:
> greened at obbligato.org (David A. Greene) writes:
>
>> I can't use git-svn to pull because we use svn on our end.  One
can't do
>> this:
>>
>> (Upstream) svn <--> git-svn <--> git <--> git-svn
<--> svn (Downstream)
>>
>> because the revisions in the two svn repositories don't have
anything to
>> do with each other.
> But if you want to transfer revisions from LLVM's svn to your svn repo,
> maybe you can do that:
>
> (Upstream) svn <--> git-svn <--> svn (Downstream)
>
> You would use two git-svn branches on the git repo, one for each svn
> repo, and merge revisions among the two. I'm not user if that's
> possible, though. Another option is to use two git-svn repos:
>
> (Upstream) svn <--> git-svn <--> git-svn <--> svn
(Downstream)
I asked about both to the git guys.  They said it isn't supported.
Double-ended git-svn just won't work, period.  You can't do it because a
git branch is still tied to the revision numbering of the first git-svn
gateway created.  Git branches still must relate to each other, they
can't run independently or one wouldn't get any merging benefit.
>> It would be even better if LLVM had a git mirror that could push
changes
>> to svn as well but let's do things one step at a time.  :)
>
> The difficult part is not on LLVM's using svn, the problem is on you
> using svn.
Umm...that's more than a bit off-putting, thanks.  If it's a problem to
use svn (and it IS a problem), then it's a problem on BOTH ends.  That
is in fact why people are asking about it.  Remember, it ain't just me.
I didn't even bring up this current thread.

And to be clear, the root of the problem _is_ LLVM's using svn because
it doesn't allow the kind of distributed development natural to an open
source project.  If one is not supposed to use svn (the official blessed
LLVM SCM) on "our side," pray tell, what _are_ we supposed to use?
> And for a git mirror that pushes changes to the LLVM svn repo, that's
> *way* more tricky than it seems.
I suspect for exactly the same reasons git-svn isn't tenable in general.
svn is just bad business all around.

                         -Dave

greened at obbligato.org (David A. Greene) writes:
>> (Upstream) svn <--> git-svn <--> git-svn <--> svn
(Downstream)
>
> I asked about both to the git guys.  They said it isn't supported.
> Double-ended git-svn just won't work, period.  You can't do it
because a
> git branch is still tied to the revision numbering of the first git-svn
> gateway created.  Git branches still must relate to each other, they
> can't run independently or one wouldn't get any merging benefit.
My point is that you can use two git repositories, each one tracking one
svn repo, and move revisions from one to another. I never tried it so
don't know how well it works. You may be right about the difficulty of
merging (you would be rebasing all the time, to be precise, but anyways
you are forced to rebase if you are using git-svn on one end.)
>> The difficult part is not on LLVM's using svn, the problem is on
you
>> using svn.
>
> Umm...that's more than a bit off-putting, thanks.
Sorry, thas was not my intention. There was an smiley somewhere around
there.
> If it's a problem to
> use svn (and it IS a problem), then it's a problem on BOTH ends.
I'll say that your svn is creating more trouble than LLVM's svn when you
are ready to send your changes upstream. After all, you are the
developers (working on "feature branches"), while LLVM's svn can
be
considered the "master branch". This applies too in case you have a
private branch. As you say, git makes merging an easy task and keeping a
private branch is about merging all the time.
> That is in fact why people are asking about it.  Remember, it ain't
> just me.  I didn't even bring up this current thread.
>
> And to be clear, the root of the problem _is_ LLVM's using svn because
> it doesn't allow the kind of distributed development natural to an open
> source project.
I agree that git has lots of advantages over svn, precisely for the type
of project LLVM is (not only open source, but with a focus on quality
and stability while the typical major feature requires lots of time,
careful programming, tests and reviews.)
> If one is not supposed to use svn (the official blessed
> LLVM SCM) on "our side," pray tell, what _are_ we supposed to
use?
Because LLVM chose to use svn at some point on the past (when
distributed tools were not so mature and undestood as they are now) and
because there is no enough perception of the advantages associated with
a change, it is no excuse for you not doing what is most convenient for
your work.

Or do you think that convincing your managers about the change is more
difficult than convincing the LLVM admins? ;-)

[snip]

On Jan 31, 2011, at 7:27 PM, Óscar Fuentes wrote:
>> 
>> If one is not supposed to use svn (the official blessed
>> LLVM SCM) on "our side," pray tell, what _are_ we supposed to
use?
> 
> Because LLVM chose to use svn at some point on the past (when
> distributed tools were not so mature and undestood as they are now) and
> because there is no enough perception of the advantages associated with
> a change, it is no excuse for you not doing what is most convenient for
> your work.
We could switch back to CVS...

-Chris

Óscar Fuentes <ofv at wanadoo.es> writes:
>> I asked about both to the git guys.  They said it isn't supported.
>> Double-ended git-svn just won't work, period.  You can't do it
because a
>> git branch is still tied to the revision numbering of the first git-svn
>> gateway created.  Git branches still must relate to each other, they
>> can't run independently or one wouldn't get any merging
benefit.
>
> My point is that you can use two git repositories, each one tracking one
> svn repo, and move revisions from one to another. I never tried it so
No, we can't.  Git doesn't work that way.  Git uses a set of
repositories all cloned fronth each other.  One can't simply merge from
one arbitrary git repository to another.
>>> The difficult part is not on LLVM's using svn, the problem is
on you
>>> using svn.
>>
>> Umm...that's more than a bit off-putting, thanks.
>
> Sorry, thas was not my intention. There was an smiley somewhere around
> there.
No problem.  e-mail is tough to get right.  :)
>> If it's a problem to
>> use svn (and it IS a problem), then it's a problem on BOTH ends.
>
> I'll say that your svn is creating more trouble than LLVM's svn
when you
> are ready to send your changes upstream. After all, you are the
> developers (working on "feature branches"), while LLVM's svn
can be
> considered the "master branch". This applies too in case you have
a
> private branch. As you say, git makes merging an easy task and keeping a
> private branch is about merging all the time.
I certainly don't want to be using svn.  Believe me, if I could dump svn
this afternoon, I absolutely would.

The problem with svn is there is no "master branch" in the sense of
git.
One can't easily keep a private repository of LLVM because svn is by
nature centralized.
> Because LLVM chose to use svn at some point on the past (when
> distributed tools were not so mature and undestood as they are now) and
> because there is no enough perception of the advantages associated with
> a change, it is no excuse for you not doing what is most convenient for
> your work.
Again, the problem is that there is no convenient solution.  Everything
involves manual diff+patch at some point.  This is entirely because svn
is not a distributed SCM.

The reasons for using svn in the past were entirely correct.  But the
technology has advanced far beyond what it was back then.  I am not
demanding any sort of change, just pointing out what the cost of the
current system is.  An official git mirror would solve about half of the
current problems and that's probably good enough for most people.

                               -Dave