dockerTools.buildImageWithNixDb: simplifications and switch to closure info

[nlewo]

Since Nix 2 is now the stable Nix version, we can use closureInfo
which simplifies the Nix database initialisation (size and hash are
included in the "dump").

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

---

[nlewo]

@GrahamcOfBorg test docker-tools

[GrahamcOfBorg]

Success on aarch64-linux

Attempted: tests.docker-tools

No partial log is available.

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: tests.docker-tools

Partial log (click to expand)

syncing
docker: running command: sync
docker# [   90.731468] dhcpcd[764]: veth628c80a: removing interface
docker: exit status 0
test script finished in 92.21s
cleaning up
killing docker (pid 597)
vde_switch: EOF on stdin, cleaning up and exiting
vde_switch: Could not remove ctl dir '/build/vde1.ctl': Directory not empty
/nix/store/8pwfayhwizmspxiiqiq55r3ww37a72ry-vm-test-run-docker-tools

[FRidh]

If I am correct we already rely on Nix 2 features so I don't see any reason why not.

[dingxiangfei2009]

contents can be a list of derivations. It can also be one single derivation that defines the docker image layer.
See this:

nixpkgs/pkgs/build-support/docker/default.nix

Line 268 in 2f9fc89

let contentsList = if builtins.isList contents then contents else [ contents ];

[nlewo]

Would have been nice to have typed Nix here :)
I fixed this. Thanks!

[dingxiangfei2009]

Where is the closure?

[nlewo]

The closure is copied by the buildImage function. This copy was needed to do the --check-contents at the layer level. This is no longer required (with Nix 2.0) to initialize correctly the database.

[dingxiangfei2009]

Ah, I see.

[nlewo]

@FRidh yes, it seems now we can. In fact, I already submitted this PR 6 months back but it was too early to rely on Nix 2 features.