Building workspace library crates as an intermediate step

[BenChand]

Hi,

I have a large project I'm converting to use crane via the workspace template on crane.dev. The project is split into crates/bins/* and crates/libs/*. While I see a large performance improvement from caching all the cargo deps, I'm wondering what happens with the libs? I get the feeling that each binary getting built also has to compile all the libs, which is a lot of repeated work. Please correct me if this isn't the case!

Otherwise, is it possible to write an intermediate step that compiles the libs so the bins can re-use them?

Something like this:

cargoArtifacts = craneLib.buildDepsOnly commonArgs;
libs = craneLib.buildPackage {
  # use cargoArtifacts here
  src = crates/libs/*;
};

bin = craneLib.buildPackage {
  # use cargoArtifacts AND libs here
  src = crates/bins/my-server;
}

[BenChand]

This seems to work:

cargoArtifacts =
  let
    deps = craneLib.buildDepsOnly commonArgs;
  in
  craneLib.buildPackage (
    commonArgs
    // {
      inherit (craneLib.crateNameFromCargoToml { inherit src; }) version;
      pname = "workspace-libs";
      cargoExtraArgs = "--workspace --lib";
      src = fileSetForCrate ./crates/libs;
      cargoArtifacts = deps;
      # We want to install the artifacts so that we can use them in the bins
      doInstallCargoArtifacts = true;
      # We want to run the tests for the libs
      doCheck = true;
    }
  );

[ipetkov]

I'm wondering what happens with the libs? I get the feeling that each binary getting built also has to compile all the libs, which is a lot of repeated work

You can infer from the build logs (and/or specify --verbose when building for more context) to see if anything is being rebuilt. Assuming that building the bins doesn't change how features are unified, then I think your solution here is the correct one (first only build with --workspace --lib, then chain that into another derivation which builds the actual binaries)