RFC: migrating to git

[Iavor Diatchki]

Hello,

On Mon, Jan 10, 2011 at 12:49 PM, Roman Leshchinskiy <rl at cse.unsw.edu.au>wrote:

> On 10/01/2011, at 13:27, Simon Marlow wrote:
> > It would be a prerequisite to switching that a GHC developer only has to
> use one VCS.  So we either migrate dependencies to git, or mirror them in
> GHC-specific git branches.
>
> I'm not sure how that is going to work. It might well be possible to build
> GHC using only git. But most GHC developers also contribute to various
> libraries which are often quite intimately linked to GHC. In particular, GHC
> patches are often accompanied by library patches. Unless all those libraries
> switch to git, too, we'll have to use both git and darcs which would be
> *really* annoying.
>

If GHC and the libraries on which it depends were in git (migrated, or
mirrored), then we could use git sub-modules to track the dependencies
between changes to GHC and changes to the libraries.

Roughly, the workflow would be like this:
1. Make a change to the library and commit it.
2. Make a change to GHC.
3. Make a GHC commit which records the change and the dependency on the
commit in the library repository.

This is useful because when someone gets the changes to GHC, they would know
that they need to update their library as well (and there is tool support to
make all updates automatically). This kind of dependency is not at all
obvious with our current workflow.

The same method works for going back to a previous state of the project,
where one can "rewind" the libraries to their old versions too.

-Iavor
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