The LSST software build tool setup script (in bin/setup.sh) currently assumes that the user is using a bash shell. Running this command from zsh doesn't generate any visible warnings, but since zsh doesn't know what to do with $BASH_SOURCE, it just leaves it blank, resulting in $LSSTSW being (silently!) set to the parent directory of the right directory instead of the right directory.

I think it should be pretty easy to just make a separate setup script for zsh (and (t)csh for that matter too), similar to what's already in $LSSTSW/eups/current/bin/. As far as I can tell, only the setup script needs to be duplicated, since the rest (e.g., rebuild) start with a bash she-bang to change the shell anyway.

Part of this issue should also be to modify the instructions at https://developer.lsst.io/build-ci/lsstsw.html to reflect the possibility of different shells.