Moving MITgcm code from GCM GC repo to Ocean preserving the history

MITgcm-move.md

Much of this is based on https://vivekdhami.com/post/git-move-repo-files-with-history/

0. First you need some preliminaries. If you are on a mac, you can do:

brew install git-filter-repo

If you are on discover, do:

module load python/GEOSpyD/Min4.11.0_py3.9 other/git-filter-repo

1. Clone the two repos we need

git clone git@github.com:GEOS-ESM/GEOS_OceanGridComp.git
git clone git@github.com:GEOS-ESM/GEOSgcm_GridComp.git

2. Checkout the branch in GCM GC

cd GEOSgcm_GridComp
git checkout feature/atrayano/MITgcm-DYAMOND

3. Use filter-repo to abstract just the Ocean Grid Comp directory

git filter-repo --subdirectory-filter GEOSogcm_GridComp/GEOS_OceanGridComp --force

4. Use filter-repo to get just the files we care about

git filter-repo --path CMakeLists.txt --path GEOS_OceanGridComp.F90 --path MIT_GEOS5PlugMod --force

5. Now we move to the other repo

cd ../GEOS_OceanGridComp

6. Add source repo as a remote

git remote add source-repo ../GEOSgcm_GridComp

7. Grab the branch we need

git fetch source-repo
...
git branch feature/atrayano/MITgcm-DYAMOND remotes/source-repo/feature/atrayano/MITgcm-DYAMOND

8. When you clone GEOS_OceanGridComp, you are on develop, so we make a new branch

git checkout -b merge-mitgcm

9. Now merge

git merge feature/atrayano/MITgcm-DYAMOND --allow-unrelated-histories

In my testing this threw a couple conflicts:

Auto-merging CMakeLists.txt
CONFLICT (add/add): Merge conflict in CMakeLists.txt
Auto-merging GEOS_OceanGridComp.F90
CONFLICT (add/add): Merge conflict in GEOS_OceanGridComp.F90
Automatic merge failed; fix conflicts and then commit the result.

that need solved.