nixosTests.clangd: init

[jchv]

Implements a NixOS test for clangd. I was inspired to do this because clangd broke on master and I figured it would be a good idea to have a test for it.

Since the fix is only in staging, I figured targeting staging would make sense. That way the test can fly alongside the fix, which is in #462747.

Related to #463367.

Things done

• Built on platform:
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• Tested, as applicable:
  • NixOS tests in nixos/tests.
  • Package tests at passthru.tests.
  • Tests in lib/tests or pkgs/test for functions and "core" functionality.
• Ran nixpkgs-review on this PR. See nixpkgs-review usage.
• Tested basic functionality of all binary files, usually in ./result/bin/.
• Nixpkgs Release Notes
  • Package update: when the change is major or breaking.
• NixOS Release Notes
  • Module addition: when adding a new NixOS module.
  • Module update: when the change is significant.
• Fits CONTRIBUTING.md, pkgs/README.md, maintainers/README.md and other READMEs.

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[Patryk27]

fwiw, I think this can be simplified - I've also added clangd tests as a part of different pull request some time ago 👀

https://github.com/NixOS/nixpkgs/pull/354755/files#diff-42653c93e96edaa584f7622ef3f704df67a115ad7da505b04f06f2cf45c3e54bR54

[jchv]

Oh, that's much nicer. In that case, I don't see much of a reason to keep this PR open. Hopefully that PR can be merged soon.

Are passthru tests visible anywhere obvious? I basically just wanted to find a way to make clangd breakages visible faster so they wouldn't make it out of staging as easily.

[Patryk27]

Are passthru tests visible anywhere obvious?

I thiiink they are not automatically propagated anywhere, so adding an explicit entry to all-tests.nix is still a good idea - I'll take a look at that over the weekend!