bld

bld is an experimental build tool for monorepos inspired by Bazel, and implemented with Nix. This is meant to evolve and its current form is not the final one.

This tool has two sides: a CLI and a Nix library, that are meant to be able to work together.

Principles

We steal the notion of "targets" from Bazel, making each folder open-ended.

It should be possible to type bld in any folder and get the build output of the current folder (and below?).

It should be possible to build any targets using purely nix-build.

Usage

$ bld --help

Usage: bld <command>

Flags:
  -h, --help     Show context-sensitive help.
      --debug

Commands:
  build [<target>]
    Build target

  list [<target>]
    List available targets

  run [<target>]
    Run executable target

  inspect [<target>]
    Show build information about target

Run "bld <command> --help" for more information on a command.

The following examples are from this repository.

To list all targets.

$ bld list

bin
default
devShell
hello

To build a target.

$ bld build hello

INFO[0000] Building target                               target=hello
/nix/store/9a74wmrh6l9h012xza53ff58v0rx456d-hello

To run a target.

$ bld run hello

/nix/store/9a74wmrh6l9h012xza53ff58v0rx456d-hello
Hello, world!

This can be also used to pass flags:

$ bld run hello -- --help

/nix/store/9a74wmrh6l9h012xza53ff58v0rx456d-hello
Print a friendly, customizable greeting.

  -t, --traditional       use traditional greeting
  -g, --greeting=TEXT     use TEXT as the greeting message

      --help     display this help and exit
      --version  output version information and exit

Report bugs to: bug-hello@gnu.org
GNU Hello home page: <https://www.gnu.org/software/hello/>
General help using GNU software: <https://www.gnu.org/gethelp/>

To inspect a target.

$ bld inspect hello

{
  "/nix/store/bn6wpa9yqibcy83d2iabh1s5k49lcpb7-hello.drv": {
    "args": [
      "-e",
      "/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"
    ],
    "builder": "/nix/store/1b9p07z77phvv2hf6gm9f28syp39f1ag-bash-5.1-p16/bin/bash",
    "env": {
      "allowSubstitutes": "",
      "buildCommand": "target=$out'/bin/hello'\nmkdir -p \"$(dirname \"$target\")\"\n\nif [ -e \"$textPath\" ]; then\n  mv \"$textPath\" \"$target\"\nelse\n  echo -n \"$text\" > \"$target\"\nfi\n\neval \"$checkPhase\"\n\n(test -n \"$executable\" && chmod +x \"$target\") || true\n",
      "buildInputs": "",
      "builder": "/nix/store/1b9p07z77phvv2hf6gm9f28syp39f1ag-bash-5.1-p16/bin/bash",
      "checkPhase": "/nix/store/1b9p07z77phvv2hf6gm9f28syp39f1ag-bash-5.1-p16/bin/bash -n -O extglob \"$target\"\n",
      "cmakeFlags": "",
      "configureFlags": "",
      "depsBuildBuild": "",
      "depsBuildBuildPropagated": "",
      "depsBuildTarget": "",
      "depsBuildTargetPropagated": "",
      "depsHostHost": "",
      "depsHostHostPropagated": "",
      "depsTargetTarget": "",
      "depsTargetTargetPropagated": "",
      "doCheck": "",
      "doInstallCheck": "",
      "enableParallelBuilding": "1",
      "enableParallelChecking": "1",
      "executable": "1",
      "mesonFlags": "",
      "name": "hello",
      "nativeBuildInputs": "",
      "out": "/nix/store/9a74wmrh6l9h012xza53ff58v0rx456d-hello",
      "outputs": "out",
      "passAsFile": "buildCommand text",
      "patches": "",
      "preferLocalBuild": "1",
      "propagatedBuildInputs": "",
      "propagatedNativeBuildInputs": "",
      "stdenv": "/nix/store/p93ivxvrf3c2w02la2c6nppmkgdh08y3-stdenv-linux",
      "strictDeps": "",
      "system": "x86_64-linux",
      "text": "#!/nix/store/1b9p07z77phvv2hf6gm9f28syp39f1ag-bash-5.1-p16/bin/bash\n/nix/store/y4mxrg8c6l09lb2szl69vwl4f6441i5k-hello-2.12.1/bin/hello\n\n"
    },
    "inputDrvs": {
      "/nix/store/6pj63b323pn53gpw3l5kdh1rly55aj15-bash-5.1-p16.drv": [
        "out"
      ],
      "/nix/store/g6qkwa2xaq6i40cwl9bpjxi19m7q8121-hello-2.12.1.drv": [
        "out"
      ],
      "/nix/store/zq638s1j77mxzc52ql21l9ncl3qsjb2h-stdenv-linux.drv": [
        "out"
      ]
    },
    "inputSrcs": [
      "/nix/store/9krlzvny65gdc8s7kpb6lkx8cd02c25b-default-builder.sh"
    ],
    "outputs": {
      "out": {
        "path": "/nix/store/9a74wmrh6l9h012xza53ff58v0rx456d-hello"
      }
    },
    "system": "x86_64-linux"
  }
}

Future ideas

• Resolve the targets purely with Nix. It should be necessary to connect the BUILD.nix files manually like currently.
• Snapshot nixpkgs. In order to speed-up nixpkgs, we want to be able to snapshot the build outputs that we are going to use.
• Add nix evaluation caching to speed-up builds.
• Introduce incremental rebuild Nix libraries for various languages.
• Hook in pre-processing tools. It should be possible to update a third-party package hash automatically.