How to merge two separate repos, combine git histories, and nesting one inside a directory.

merge-two-repos-and-combine-histories.sh

https://stackoverflow.com/a/10548919/20335188

# steps to merge child-repo into parent-repo

brew install git-filter-repo # will need it later

git clone https://github.com/yourusername/child-repo.git
cd child-repo
git filter-repo --to-subdirectory-filter child-repo # rewrite history to move all files to child-repo folder

cd ..

# now we have a repo with all files in child-repo folder for git history

# we need to merge it with the parent-repo

git clone https://github.com/yourusername/parent-repo.git
cd parent-repo

# create a new branch to merge child-repo into

git switch -c merge-child-repo

# add child-repo as a new folder

git remote add child-repo ../child-repo
git fetch child-repo --tags

# merge master branch of child-repo into parent-repo
git merge --no-ff --allow-unrelated-histories child-repo/master