- Do not store the full list of environment variables in
<prefix>/.spack/spack-build-env.txt because it may contain user secrets.
- Only store environment variable modifications upon installation.
- Variables like PATH may still contain user and system paths to make
spack-build-env.txt sourceable. Variables containing paths are
modified through prepending/appending, and if we don't apply these
to the current environment variable, we end up with statements like
`export PATH=/path/to/spack/bin` with system paths missing, meaning
no system binaries are in the path, which is a bad user experience.
- Do write the full environment to spack-build-env.txt in the staging dir,
but ensure it is readonly for the current user, to make it a bit safer
on shared systems.
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