nixUnstable: 2.4pre20201102_550e11f -> 2.4pre20201105_387f824

[roberth]

Motivation for this change

Most notably

• Fix a memory corruption and deadlock caused by new constant-memory source filtering implementation (+ fix implementation error)
• Fix nix-copy-closure with drvs
• Fix a varargs error in an error message (also a crash?)

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• 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 nixpkgs-review --run "nixpkgs-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)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[Ma27]

While the change itself seems fine, I'd like to mention that Hydra doesn't build stuff anymore in hydra-queue-runner which can be reproduced by running nixos/tests/hydra on master and on this branch.

Unfortunately I don't have the time right now to look at this, but since Hydra requires nixUnstable these days, this is something that should be taken care of (cc @edolstra).

After a brief check I identified NixOS/nix@c4d903d and NixOS/nix@b43c13a to be the cause, however I acknowledge that those are relevant fixes and I don't know enough about that to patch Hydra accordingly.

[Ma27]

So just realized that with a nix-daemon on latest nix master (i.e. this revision) all started builds stall, even without Hydra making a rollback to a previous configuration necessary.

Hence 👎 on merging this.

[mohe2015]

I agree with the statement from @Ma27

[roberth]

NixOS/nix#4235 is currently the only remaining issue. I've added a patch for it to make this branch useful for testing.
I don't think we should be patching Nix here, but for now it's useful for those who want to give this PR a spin.

[nixos-discourse]

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

https://discourse.nixos.org/t/to-flake-or-not-to-flake/10047/5

[roberth]

Closing in favor of #104289, in order not to break any pins on this old branch.