nixos/top-level: add includeBuildDependencies option

[lheckemann]

Description of changes

This option allows adding the build closure of the system to its runtime closure, enabling fully-offline rebuilds (as long as no new packages are added).

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:
  • 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/)
• 22.11 Release Notes (or backporting 22.05 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.

[roberth]

I like the idea.

It's a problem I've also encountered and solved independently for nixos/tests/nixops/default.nix, but that solution required virtualisation.additionalPaths; so not immediately transferable to NixOS itself. I'm glad to see a more general and cleaner solution.
If I'm not mistaken, the nixops test could be supported the following instead of my hacky solution:

  deployer.system.extraDependencies = nodes.server.config.system.build.toplevel;
  server.system.includeBuildDependencies = true;

You might also be interested in what I've written down for a more efficient solution in #180529, but let's not work on that in this PR.

[RaitoBezarius]

Looks good to me.

[roberth]

Just some doc improvements, because I think we should be more explicit about what happens.

[roberth]

Suggested change

	Whether to include the build closure of the whole system in
	its runtime closure. This can be useful for making changes
	fully offline, as it results in all sources and patches
	required to build the system being included.
	Whether to include the build closure of the whole system in
	its runtime closure. This can be useful for making changes
	fully offline, as it includes all sources, patches and intermediate
	outputs that are required to build all the derivations.
	All derivations really means all derivations, from the bootstrapping
	tools, to the build tools, to the packages, and all the way up to the
	configuration files of the system.

[roberth]

Suggested change

	Note that this increases closure size drastically: a minimal
	This increases the system's size drastically: a minimal

... or do some people scan for "Note" in text? I don't think I do.

[RaitoBezarius]

(I do, but I am fine either way)

[roberth]

Suggested change

	Note that this increases closure size drastically: a minimal
	Note that this increases the system size drastically: a minimal

[roberth]

deployer.system.extraDependencies = nodes.server.config.system.build.toplevel;
server.system.includeBuildDependencies = true;

This works when enabled on the deployer instead, which makes more sense anyway.

[roberth]

You may include my nixops test patch, although I'd prefer a simple stand-alone test that doesn't involve a specific deployment tool, but just NixOS.

0001-nixosTests.nixops.unstable.legacyNetwork-Use-system..patch.txt

Refs

• A function rebuildDependencyClosure that produces an efficient closure for offline rebuilds #180529

[roberth]

I don't think the build is much slower, is it? Isn't this more about substituting many more dependencies?

[lheckemann]

You're absolutely right. Building the system entirely from scratch without substitution should take pretty much the same amount of time as before.

[roberth]

Thanks @lheckemann for polishing the implementation. I'll add this to the nixops test so that it's tested at least somewhere.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/declarative-vms-ubuntu-on-top-of-nixos/34592/2