lib/filc-system.nix
The Fil-C system: a NixOS or finix machine whose pkgs is filnix's Fil-C package set. NixOS and finix modules pick their programs from pkgs, so systemd or finit, PAM, D-Bus, OpenSSH and every service are Fil-C builds without being named here. The kernel, the bootloader and the other packages in lib/native-exceptions.nix come from native Nixpkgs, and so do the ones you add:
nixos/default.nix and finix/default.nix import this with their os and add what differs between the two.
The user's exceptions, as given to the package set.
Every node that sets nothing shares one package set: each one made here is a fresh Nixpkgs import.
The store paths of the native exceptions. filc-ps allows a native process whose program is in one's closure. Without string context, so an exception the system does not use is not pulled into it.
Its definitions are this file's, not those of the module importing it.
Not read from nixpkgs.*: this module sets nixpkgs.pkgs, which makes those options unreadable.
Packages to take from the native package set instead of building them with Fil-C, as a function of that set. Use it for Rust and Go programs you want anyway, and for C programs that do not work yet. Each one runs as an ordinary native process with native libraries. A name the native set does not have fails evaluation. The packages in filnix's lib/native-exceptions.nix are always native.
The native package set that the exceptions come from. By default, filnix's own Nixpkgs, imported natively. Your usual Nixpkgs works too and gets its binary cache hits.