NixOS/evalModules legacy cleanup

[roberth]

Motivation for this change

The supposedly legacy args flags was still used and was not passed along correctly. This PR fixes this at the module system level, at the NixOS level and in the documentation module. While only one of these would be sufficient to solve the issue, it is clear that we should get rid of the redundant code.

• First and foremost, address the issue raised in nixos/specialisation: Rephrase in terms of extendModules, noUserModules #144094 (comment).

• Deprecate the legacy parameters that, combined with nixos/specialisation: Rephrase in terms of extendModules, noUserModules #144094, created the problem.

• Simplify the documentation module and make it more complete and accurate.

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • The fix is to simplify, so that a new test case is not necessary
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.05 Release Notes (or backporting 21.11 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[FlorianFranzen]

This seems to fix #148343 for me.

It then started to fail with FileNotFoundError: [Errno 2] No such file or directory: '/nix/store/<hash>-source/kernel', so I also needed to apply #132688 to fix systemd-boot with specializations again.

[infinisil]

Nice cleanup! I can confirm that this fixes specialisations

[nh2]

@roberth @infinisil There is one location remaining in nixpkgs that sets these deprecated args and check:

nixpkgs/lib/modules.nix

Lines 1073 to 1074 in 0ed4113

	/* Compatibility. */
	fixMergeModules = modules: args: evalModules { inherit modules args; check = false; };

Could/should this be rewritten?

[infinisil]

@nh2 fixMergeModules should really be fully deprecated, could you try that? It looks like Nixops still uses it even though it should've been removed some time ago, so a Nixops PR to remove that would be good. Nixpkgs would have to wait a bit with deprecation then though