spack update: like brew update, but for spack

A command that behaves like Linuxbrew/Homebrew's brew update. That is, it:

• fetches develop from origin
• merges fetched develop where appropriate
• possibly stashes existing changes on current branch, checks out develop, pulls develop (i.e., git-fetch and git-merge), checks out the old current branch, and re-applies stashed changes
• does not install or build anything
• does not do anything more than fetch/merge/stash/unstash operations on the local git repo copy of someone's spack installation

Rationale

Right now, to update spack, I need to

pushd ${SPACK_ROOT}
git checkout develop && git fetch origin && git merge --ff-only origin/develop && \ 
git checkout $MY_OLD_BRANCH # or use git-pull, or simiilar
popd

whereas to do something vaguely equivalent in Homebrew is brew update. Consequently, it's way easier to stay up-to-date with homebrew-core/master than it is to stay up-to-date with spack.

Description

See above for longer description. Succinctly, I'd like a spack-update command that behaves like brew-update does for Homebrew/Linuxbrew.

Alternatives

• Do nothing. Fine by me, but the number of commands required slows me down in comparison to running a single command to update my copy of spack's github repo.
• Have spack update do more stuff, like actually upgrade packages, potentially even in-place, or install new packages; I think adding more functionality to the general idea of "implement a single command that just keeps the spack repo up-to-date and nothing else" starts into feature creep.