Add SPACK_DISABLE_LOCAL_CONFIG (back in)?

[climbfuji]

Is your feature request related to a problem? Please describe.

We have users who do their own spack business, but then also install the environments that we provide, and quite often we trip over customizations they made in their ~.spack directories. We already have our environments set up to bootstrap into the environment directory and write any config files there, but spack is still reading from ~/.spack, even though it's no longer writing to it (exception: when running spack bootstrap now outside an active environment).

Describe the solution you'd like

A while back, we tried to add

export SPACK_DISABLE_LOCAL_CONFIG=true

to setup.sh. This, together with SPACK_USER_CACHE_PATH=..., which we already set in setup.sh, causes spack to ignore ~/.spack entirely.

The problem is, however, that we need an automated mechanism to register an existing spack bootstrap mirror where needed (i.e. air-gapped systems) and then bootstrap from that. This is because with SPACK_DISABLE_LOCAL_CONFIG=true and SPACK_USER_CACHE_PATH=..., spack will bootstrap from scratch every time a new spack-stack code is checked out and environments are installed from it.

Additional context

A few weeks back, I contributed bug fixes to spack develop and our fork (based on spack v0.23) that fixed the broken logic to create and use bootstrap mirrors. These bugs would have blocked the above approach, but fortunately they are now gone.