Settings aliases are not supported as flags, while their "real" names are

[cole-h]

Describe the bug

It is possible to specify nix.conf options on the command line with --<option name> <option value if necessary> (as opposed to --option <option name> <option value if necessary>). However, this does not appear to extend to aliases.

When running nix eval --expr '{}' --build-cores 0, the --build-cores flag is unrecognized. However, passing it as an --option allows it to work.

Steps To Reproduce

1. Install Nix 2.23.1
2. Run nix eval --expr '{}' --build-cores 0
3. See error that build-cores is not recognized (despite there being an alias to it from cores)
4. Try again with --cores 0 and see it succeed

This is reproducible for all settings with aliases.

Expected behavior

Aliases of nix.conf settings should work when passed as a flag, without needing to resort to --option <setting alias name> <value>

nix-env --version output

Reproduced on nix-env (Nix) 2.21.2, nix-env (Nix) 2.23.1, and nix-env (Nix) 2.24.0pre20240617_daf1b6b

Additional context

Priorities

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[roberth]

Triage (Nix team):

Looks like a legitimate missing piece of logic.
We have an issue where we're able to pass -- flags for options that aren't relevant, but that's a separate issue and not a reason to block a fix for aliases.