Git: Move files and history from oldrepo to newrepo

Example commands show moving the "data" directory from oldrepo to newrepo and includes all history.

oldrepo (the source)

Clone a fresh copy of oldrepo.

git clone [email protected]:USERHERE/oldrepo.git
cd oldrepo

Optional: git-filter-repo if you want to prune history to match certain dirs/files.

# Example (multiple "--path file" or "--path dir" args may be passed, space separated)
git filter-repo --path data

Clone a fresh copy of newrepo.

git clone [email protected]:USERHERE/newrepo.git
cd newrepo

Checkout the branch on newrepo that you want to merge oldrepo into.
```
git checkout develop
```
Add a new remote that tracks the local oldrepo.
```
git remote add local-oldrepo ../oldrepo/
```
Fetch branches from the local oldrepo 'remote':
```
git fetch local-oldrepo
```
Create a new temporary branch on newrepo that tracks the local 'remotes/local-oldrepo/branch' as an upstream.
```
git branch develop-tmp remotes/local-oldrepo/main
```
Merge the newly created temporary branch into the currently checked out branch on newrepo. (In this example, develop is still checked out on newrepo.)
```
git merge develop-tmp --allow-unrelated-histories
```
- You may have to deal with merge conflicts for commonly named files.
Push your branch to the upstream git server (once satisfied with the results)
```
git push --set-upstream origin develop
```

Remove newrepo's remote reference to the local oldrepo and the temporary branch that tracked it.

git remote rm local-oldrepo
git branch -d develop-tmp

Remove oldrepo's local copy.

rm -rf oldrepo