Migrating a branch from fcm to git#

Important

If migrating an old trac ticket, please make sure to,

Cross-link between both the trac ticket and github PR/Issue
Add a git_migration:#NNN keyword to the trac ticket to avoid duplicate migrated tickets

This page is intended to act as a guide when migrating branches from fcm to git after the initial git release. It assumes that you have already created a fork of the repo you are migrating to.

Important

The process below involves rsyncing the changes in your fcm working copy to a git clone. This requires that the two branches have equivalent branch points, so ensure this is the case.

For convenience, the git_migration tag is provided as a branch point in both fcm and git. However all fcm revisions and tags have a direct equivalent commit on git - tags will have the same name on both, revisions of specific commits will need to be manually aligned with a commit hash by comparing commit messages.

Optionally, create a new branch in fcm using the tag git_migration. Then merge your development branch onto this one, eg.
```
fcm bc --type=dev branch_for_migration fcm:lfric_apps.x_tr@git_migration
...
fcm merge fcm:lfric_apps.x_br/dev/USER/BRANCH
```
Resolve any conflicts and then commit these changes to this branch, fcm ci.

For Jules users, upgrading to the git_migration tag is required.
Move into your git clone and create a new branch with the same start point as your fcm branch. If you are branching from an untagged revision, you will need to manually find the relevant hash for that commit from the git log by comparing commit messages.
```
git switch -c <branch name> <tag/hash to branch from>
e.g. git switch -c new_migrated_branch git_migration
```
If the git_migration tag doesn’t exist in your clone, then you may need to sync tags.
Rsync the changes over from the fcm working copy to the git clone. Use --delete to remove any files you have deleted in your branch. Use --exclude=.git --exclude=.svn so that the version control directories aren’t modified.
```
# NOTE: You need the trailing backslash on the fcm source path
rsync -av --delete --exclude=.git --exclude=.svn path/to/fcm/working/copy/ path/to/git/clone
```
Check carefully the output of the rsync via git status. If you have new files on your branch these will need adding via git add.
Finally, all branches will need to update to the initial git release in order to run the test suites. This can be done by merging the stable branch into your new branch. See updating a branch for more details, noting that you will need to use one of the options using git commands for this step.

If you have a linked ticket you will manually need to update the dependencies.yaml to point at your linked branches. For lfric_apps branches, ensure that the dependencies.sh file hasn’t been readded to the branch.
It may be worth running the test suite to ensure the branch has been properly migrated.

Tip

There will be significant changes to the rose-stem test suites between the git_migration point and the initial git release. Therefore, conflicts are expected when updating rose-stem changes to the initial release. The UM, Jules and UKCA test suites have all had file extensions renamed from .rc to .cylc.

For lfric_core a minor source code change has been added to github, which may result in conflicts in components/lfric-xios/source/lfric_xios_file_mod.f90