Z Shell

To upgrade to a new version of zsh:

1. Checkout dev/UPSTREAM.
2. Replace its contents with the new version.
3. Rename zsh/.gitignore to zsh/.gitignore.dist.
4. Commit and push the new content.
5. Create an eng/ branch.
6. git merge dev/UPSTREAM into your branch and resolve any conflicts.
7. Review, test, and nominate that eng/ branch.