Best way to setup debug builds in the CI?

[dpc]

Right now crane default to --release builds, and rightly so - because that's kind of the default, where the artifacts built by the flake should be prod-usable.

However, when used in CI, it seems like a waste of time to build the release mode.

So here is the question - what would be the neatest way to parametrize the existing build (flake.nix with a complex setup like I have to expose debug-builds to use in CI.

[ipetkov]

Easiest way? Set CARGO_PROFILE = "dev"; in the derivation and all cargo invocations will effectively run as cargo --profile dev (which is the default "debug" profile used by cargo)

It's worth noting that cargo considers debug and release artifacts to be different, so if your CI doesn't build production/release builds your consumers may need to build it themselves (but you might not care about this).

I'd also note that you should be careful not to mix debug cargoArtifacts built with a derivation which expects to do a release build. Cargo will happily compile everything, but effectively you won't get any benefits of artifact caching.

It's also technically possible to build and cache both release and debug artifacts, but that will result in a lot more data being cached/copied around, so pick your poison

# Build both debug and release artifacts, be careful with cache bloat!
let
  src = ./whatever;
  cargoArtifactsDebug = craneLib.buildDepsOnly {
    inherit src;
    CARGO_PROFILE = "dev";
  };

  cargoArtifactsReleaseAndDebug = craneLib.buildDepsOnly {
    inherit src;
    cargoArtifacts = cargoArtifactsDebug;
    CARGO_PROFILE = "release";
  };
in
{
  myCrateRelease = craneLib.buildPackage {
    inherit src;
    cargoArtifacts = cargoArtifactsReleaseAndDebug;
    CARGO_PROFILE = "release";
  };

  myCrateDebug = craneLib.buildPackage {
    inherit src;
    cargoArtifacts = cargoArtifactsReleaseAndDebug;
    CARGO_PROFILE = "dev";
    };
}

[dpc]

That's so good, maybe it should be illegal.

[dpc]

Oh, wait ... but this will not fix the CARGO_PROFILE in derivation pointed at by cargoArtifacts... Hmm...

[ipetkov]

D'oh, you're totally right! Guess the lambda it is then...

[ipetkov]

Actually I wonder if you could also recurse into .overridrAttrs (old: { cargoArtifacts = old.cargoArtifacts.overrideAttrs (...); } 🤔

Probably not worth the headache to express with Nix but it might be doable

[dpc]

     let debug =
            let overrideCargoProfileRec = deriv: profile: deriv.overrideAttrs (oldAttrs: { CARGO_PROFILE = profile; cargoArtifacts = if oldAttrs ? "cargoArtifacts" && oldAttrs.cargoArtifacts != null then overrideCargoProfileRec oldAttrs.cargoArtifacts profile else null; });
            in builtins.mapAttrs (name: deriv: overrideCargoProfileRec deriv "dev") packages;

A little bit of recursion fixed it.