I've just tried to upgrade from v4.2.13 to 4.3, and at the git checkout stage, it complains with:
error: Your local changes to the following files would be overwritten by checkout:
config/environments/production.rb
yarn.lock
Please commit your changes or stash them before you switch branches.
I have no idea how to use "git stash" to get out of the problem.
I used git stash to store it, ran checkout again which succeeded, but when I tried to stash pop it, it complained the file needed merging.
I have no idea what to do next, and the release notes don't explain that this step could be needed.