Migrating patches from darcs to git

Suppose ghc/darcs is a darcs GHC tree containing patches that need to be migrated to git, and ghc/git is a git GHC tree. We're not going to try to preserve the history; just get the code into the repo.

This assumes that all your changes are in the ghc repo itself. Otherwise, if you have made changes to other repos (e.g. libraries/base) you'll need to do a similar procedure for those repos too.

We'll assume the following directory setup, where $root is some directory in your file system

• $root/my-darcs: the Darcs repo that contains the patches you'd like to move over into Git. We will make no changes to this repo.
• $root/baseline-git (initially non-existent): the Git repo at the moment of switchover
• $root/migrate (initially non-existent): during the transfer process this is going to be both a Darcs repo and a Git repo

Step 1: create migrate:

cd $root
darcs checkout http:://darcs.haskell.org/ghc
mv ghc migrate

This gets a Darcs copy of the repo, precisely at the switchover point. (We don't need a tag, because the Darcs repos were frozen precisely at switchover, so the HEAD will do.)

Step 2: create baseline-git:

cd $root
git clone ghc/git baseline-git
cd baseline-git
git checkout -b "some-descriptive-name" ghc-darcs-git-switchover

SLPJ: the clone command should mention the actual URL, not assuming you have a current copy. This gets a Git copy of the repo, precisely at the point of switchover (that's what the ghc-darcs-git-switchover tag does). At this moment all the source files in migrate and baseline-git should be bit-for-bit identical. Check this.

Step 3: make migrate/ into a Git repo too! All we need do is to copy over Git's meta-data.

cd $root/migrate
mv ../baeline-git/.git .

Step 4: transfer patches. For each patch (or group thereof) you want to transfer, do this:

• Pull the patch into tmp-git:

  cd $root/migrate
  darcs pull ../my-darcs
   ...interactively pull the patches you want...
  

• Record a Git patch for this patch group

  git commit -a
  git checkout master
  git merge "some-descriptive-name"
  

SLPJ: is this commit/checkout/merge thing right? Do you need to switch back to a branch for the next pull? Do you get to write a commit message?

Step 4: validate and push to Git.

---

old version

First, make a backup of the darcs repo in case something goes wrong:

cp -a ghc/darcs ghc/backup-darcs

Now make sure ghc/darcs is fully up-to-date:

cd ghc/darcs
./darcs-all pull -a
cd ../..

Next we checkout the git repo as it was at the darcs branch point:

git clone ghc/git ghc/migrate
cd ghc/migrate
git checkout -b "some-descriptive-name" ghc-darcs-git-switchover
cd ../..

Now we put the git meta-data into our darcs repo, record the changes with git and merge them back to master:

cd ghc/darcs
mv ../migrate/.git .
git commit -a
git checkout master
git merge "some-descriptive-name"
cd ../..

Finally, we pull the changes into our real git repo:

cd ghc/git
git pull ../../ghc/darcs master

The ghc/migrate directory is no longer needed and can be removed.