RFC: migrating to git

Thomas Schilling nominolo at googlemail.com
Mon Jan 10 17:19:58 CET 2011

I'd be for a move, but haven't contributed much lately.  I use Git for
all my personal projects, so I consider Git to be useful.  I
personally find sending patches via Git to be harder than with Darcs,
but if we use Github the pull-request-based model should work well.

I used Git on Windows two years ago and didn't have any problems (the
case sensitive file name issue has a well-documented setting to avoid
issues).  I think I used msysGit and used msys to build GHC, so those
should work well together.  (Granted, though, I used Git only for a
small code base at the time.)

We'd probably have to adopt the workflow that Johan linked to
(separate branch for every larger change, merge with --no-ff) but that
might actually improve things (e.g., unmerging a branch if necessary).

The important issues, mentioned by Max, remain and I agree that GHC HQ
should have the last decision on these.

On 10 January 2011 11:19, 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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Push the envelope. Watch it bend.

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