I agree with the change of terminology (command-line scope -> custom scope)

There is a remaining use of the term "command-line scope" that needs to be updated. Once that's done ping me and I'll merge this.

I like the new terminology.

You might consider changing the help text for spack -H to say "add a custom configuration scope" instead of "use an additional configurations scope".

I'm looking at some of the internals in lib/spack/spack/config.py and lib/spack/spack/main.py and I'm noticing a command_line scope. It seems to be used for both command-line settings as well as custom config files. I'm hesitant to make any changes to this so close to SC, but I also hate leaving things out of sync with the docs. It seems like right now, these two scopes have the same precedence, which isn't ideal in my mind.

I'm looking at some of the internals in lib/spack/spack/config.py and lib/spack/spack/main.py and I'm noticing a command_line scope.

Internally it may assign variable names like custom scope but that can be adjusted later

It seems like right now, these two scopes have the same precedence, which isn't ideal in my mind.

They are treated as separate scopes so one will definitely have precedence, and Spack should arrange when pushing scopes to preserve the command line scope (as we refer to it here) as the highest precedence one