Currently, setting `homebrew.masApps` causes `"mas"` to automatically
be added to `homebrew.brews`. Users who want to use Homebrew only
for managing App Store apps and casks, like me, can override this
by setting `homebrew.brews = lib.mkForce [ ];` and adding Nixpkgs’
`mas` to their `environment.systemPackages`.
When the activation script path no longer depends on the built
configuration’s `environment.systemPackages`, this will no longer
work. Since this was originally added before `mas` was packaged in
Nixpkgs and we now have a perfectly serviceable binary package,
we can add it to the `$PATH` when invoking Homebrew and skip the
automatic formula installation.
As the Homebrew `bin` directory still comes first, users who
specifically want the formula can restore the previous behaviour by
explicitly adding `"mas"` to `homebrew.brews`.
Closes: #1314
c31b6e8a03