nix build hangs on Building subPackage .

[marcuswhybrow]

Hello, it's my first time using gomod2nix. My flake builds my hello world main.go, but always hangs for 8 seconds at Building subPackage . It hangs for much longer on a real project I'm attempting to transition. It feels like a setup cost I should be paying once, which is then cached, but it's happening on every code change. Am I doing something wrong?

❯ ls
flake.lock  flake.nix  go.mod  gomod2nix.toml main.go

❯ cat go.mod
module github.com/marcuswhybrow/myproject

go 1.20

❯ cat gomod2nix.toml
schema = 3

[mod]

❯ nix build  --verbose --log-format bar-with-logs
this derivation will be built:
  /nix/store/pw50p05dxlnnz16j7a9dvq1p29gcr7q0-myproject.drv
building '/nix/store/pw50p05dxlnnz16j7a9dvq1p29gcr7q0-myproject.drv'...
myproject> unpacking sources
myproject> unpacking source archive /nix/store/wycclwg1dgyrhx4j0z6w94ch707cdc8j-golang
myproject> source root is golang
myproject> patching sources
myproject> configuring
myproject> building
myproject> Building subPackage .        <-- Hangs here for 8 seconds
myproject> internal/goarch
myproject> internal/unsafeheader
myproject> internal/abi
myproject> internal/cpu
myproject> internal/bytealg
...

My flake.nix is dead simple...

{
  description = "Static Site Generator written in Golang";

  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  inputs.flake-utils.url = "github:numtide/flake-utils";
  inputs.gomod2nix.url = "github:nix-community/gomod2nix";

  outputs = inputs: inputs.flake-utils.lib.eachDefaultSystem (system: let
    pkgs = import inputs.nixpkgs {
      inherit system;
      overlays = [ inputs.gomod2nix.overlays.default ];
    };
  in {
    packages.default = pkgs.buildGoApplication {
      name = "myproject";
      pwd = ./.;
      src = ./.;
      modules = ./gomod2nix.toml;
    };

    devShells.default = pkgs.mkShell {
      name = "myproject";
      packages = [
        (pkgs.mkGoEnv { pwd = ./.; })
        pkgs.gomod2nix
      ];
    };
  });
}

I think these lines are the source of my troubles...

gomod2nix/builder/default.nix

Lines 364 to 367 in 3cbf3a5

	for pkg in $(getGoDirs ""); do
	echo "Building subPackage $pkg"
	buildGoDir install "$pkg"
	done

Thanks for any suggestions.

[peterldowns]

I've also noticed the same thing. Despite the claim that each dependency is cached, building with gomod2nix is noticeably longer than building with the nixpkgs "buildGoModule". I've switched back to that.