RFC: migrating to git

Scott Michel scooter.phd at gmail.com
Tue Jan 11 03:42:51 CET 2011

I'm inclined to vote +1 for a move to git. JP and I seem to collaborate just
fine using github for EclipseFP and scion, FWIW. I tend to develop on ad hoc
branches before I merge changes back onto the master branch.

I can't say that either of us have run into significant problems, although I
did hose myself once merging some of JP's changes onto my branch. Not a big
deal, since one will run into those problems from time to time.

Win32/64: Current msysgit hasn't caused me any significant pain. I'm not
entirely focused on performance, just getting latest patch sets from the
github repo.

Since it's just the two of us working on separate forks, I'm not sure that
either of us are pushing git to its limits. I suspect that if there are
multiple branches being developed, merging code from multiple branches into
your branch will be tough. Not sure that any VCS will help you there.

Where things will get really nasty is merging later changes to the
scion-server code back with nominolo's latest "mega patch". This is where
theory of patches or any VCS theory will just break, since the changes are
substantial. I'm not sure any VCS or DVCS will ever solve the problem of
major divergence.


On Mon, Jan 10, 2011 at 3:19 AM, Simon Marlow <marlowsd at gmail.com> wrote:

> It's time to consider again whether we should migrate GHC development from
> darcs to (probably) git.
> From our perspective at GHC HQ, the biggest problem that we would hope to
> solve by switching is that darcs makes branching and merging very difficult
> for us.  We have a few branches of HEAD that are very painful to keep merged
> with HEAD, and we would almost certainly have more branches if the overhead
> were lower.  In some sense the overhead is self-inflicted because we have
> the no-conflict policy in the mainline repository, but that is to avoid
> problems with darcs' merging algorithms (both performance and correctness).
>  We are still using darcs v1 patches rather than v2, but there are known
> problems with v2 which are preventing us from upgrading.
> The darcs team have been making great strides with performance, but
> conflict handling remains a serious problem.  The darcs roadmap doesn't show
> this being fixed in the near future
>  http://wiki.darcs.net/Roadmap
> Rebase support is coming, and it does work, though the workflow is a bit
> laborious.
> Besides the branching/merging/conflict issue, switching to git would give
> us plenty of side benefits, notably via access to a wealth of tool support.
>  Making contribution easy is important to us too, and there are a lot of
> people using git.
> The cost of switching is quite high, which is one reason we decided to stay
> with darcs last time.  We have multiple repos that need to be converted, and
> for some of them, where the repo is being shared with other projects, we may
> have to mirror rather than convert in place. We're prepared to put in the
> effort if the gains would be worthwhile though (offers of help are more than
> welcome!).
> We're intrested in opinions from both active and potential GHC
> developers/contributors.  Let us know what you think - would this make life
> harder or easier for you?  Would it make you less likely or more likely to
> contribute?
> Cheers,
>        Simon
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