Naersk

Build Rust projects with ease!

• Introduction
• Setup
• Usage
• Examples
• Tips & Tricks

Status: project's working!

Introduction

Naersk is a Nix library for building Rust projects - basically, you write:

naersk.buildPackage {
  src = ./.; # Wherever your Cargo.lock and the rest of your source code are
}

... and that turns your code into a Nix derivation which you can, for instance, include in your system:

environment.systemPackages = [
  (naersk.buildPackage {
    src = ./my-cool-app;
  })
];

# (see below for more complete examples)

Under the hood, buildPackage parses Cargo.lock, downloads all dependencies, and compiles your application, fully utilizing Nix's sandboxing and caching abilities; so, with a pinch of salt, Naersk is cargo build, but inside Nix!

If you're using Hydra, you can rely on Naersk as well because it doesn't use IFD - all the parsing happens directly inside Nix code.

Setup

Using Flakes

$ nix flake init -t github:nix-community/naersk
$ nix flake lock

Alternatively, store this as flake.nix in your repository:

{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    naersk.url = "github:nix-community/naersk";
    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
  };

  outputs = { self, flake-utils, naersk, nixpkgs }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = (import nixpkgs) {
          inherit system;
        };

        naersk' = pkgs.callPackage naersk {};

      in rec {
        # For `nix build` & `nix run`:
        defaultPackage = naersk'.buildPackage {
          src = ./.;
        };

        # For `nix develop` (optional, can be skipped):
        devShell = pkgs.mkShell {
          nativeBuildInputs = with pkgs; [ rustc cargo ];
        };
      }
    );
}

This assumes flake.nix is created next to Cargo.toml & Cargo.lock - if that's not the case for you, adjust ./. in naersk'.buildPackage.

Note that Naersk by default ignores the rust-toolchain file, using whatever Rust compiler version is present in nixpkgs.

If you have a custom rust-toolchain file, you can make Naersk use it this way:

{
  inputs = {
    flake-utils.url = "github:numtide/flake-utils";
    naersk.url = "github:nix-community/naersk";

    nixpkgs-mozilla = {
      url = "github:mozilla/nixpkgs-mozilla";
      flake = false;
    };
  };

  outputs = { self, flake-utils, naersk, nixpkgs, nixpkgs-mozilla }:
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = (import nixpkgs) {
          inherit system;

          overlays = [
            (import nixpkgs-mozilla)
          ];
        };

        toolchain = (pkgs.rustChannelOf {
          rustToolchain = ./rust-toolchain;
          sha256 = "";
          #        ^ After you run `nix build`, replace this with the actual
          #          hash from the error message
        }).rust;

        naersk' = pkgs.callPackage naersk {
          cargo = toolchain;
          rustc = toolchain;
        };

      in rec {
        # For `nix build` & `nix run`:
        defaultPackage = naersk'.buildPackage {
          src = ./.;
        };

        # For `nix develop` (optional, can be skipped):
        devShell = pkgs.mkShell {
          nativeBuildInputs = [ toolchain ];
        };
      }
    );
}

Using Niv

$ niv init
$ niv add nix-community/naersk

... and then create default.nix with:

let
  pkgs = import <nixpkgs> {};
  sources = import ./nix/sources.nix;
  naersk = pkgs.callPackage sources.naersk {};

in
  naersk.buildPackage ./.

This assumes default.nix is created next to Cargo.toml & Cargo.lock - if that's not the case for you, adjust ./. in naersk.buildPackage.

Note that Naersk by default ignores the rust-toolchain file, using whatever Rust compiler version is present in nixpkgs.

If you have a custom rust-toolchain file, you can make Naersk use it this way:

$ niv add mozilla/nixpkgs-mozilla

... and then:

let
  sources = import ./nix/sources.nix;
  nixpkgs-mozilla = import sources.nixpkgs-mozilla;

  pkgs = import sources.nixpkgs {
    overlays = [
      nixpkgs-mozilla
    ];
  };

  toolchain = (pkgs.rustChannelOf {
    rustToolchain = ./rust-toolchain;
    sha256 = "";
    #        ^ After you run `nix-build`, replace this with the actual
    #          hash from the error message
  }).rust;

  naersk = pkgs.callPackage sources.naersk {
    cargo = toolchain;
    rustc = toolchain;
  };

in
  naersk.buildPackage ./.

Usage

Naersk provides a function called buildPackage that takes an attribute set describing your application's directory, its dependencies etc. - in general, the usage is:

naersk.buildPackage {
  # Assuming there's `Cargo.toml` right in this directory:
  src = ./.;

  someOption = "yass";
  someOtherOption = false;
  CARGO_ENVIRONMENTAL_VARIABLE = "test";
}

Some of the options (described below) are used by Naersk to affect the building process, rest is passed-through into mkDerivation.

Note that you shouldn't call overrideAttrs on a derivation built by Naersk (see the note on overrideAttrs below).

buildPackage's parameters

Attribute	Description
name	The name of the derivation.
version	The version of the derivation.
src	Used by naersk as source input to the derivation. When root is not set, src is also used to discover the Cargo.toml and Cargo.lock.
root	Used by naersk to read the Cargo.toml and Cargo.lock files. May be different from src. When src is not set, root is (indirectly) used as src.
gitAllRefs	Whether to fetch all refs while fetching Git dependencies. Useful if the wanted revision isn't in the default branch. Requires Nix 2.4+. Default: false
gitSubmodules	Whether to fetch submodules while fetching Git dependencies. Requires Nix 2.4+. Default: false
additionalCargoLock	Additional cargo lock used to specify crates required for build
cratesDownloadUrl	Url for downloading crates from an alternative source Default: "https://crates.io"
cargoBuild	The command to use for the build. The argument must be a function modifying the default value. Default: ''cargo $cargo_options build $cargo_build_options >> $cargo_build_output_json''
cargoBuildOptions	Options passed to cargo build, i.e. cargo build <OPTS>. These options can be accessed during the build through the environment variable cargo_build_options. Note: naersk relies on the --out-dir out option and the --message-format option. The $cargo_message_format variable is set based on the cargo version. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ "$cargo_release" ''-j "$NIX_BUILD_CORES"'' "--message-format=$cargo_message_format" ]
remapPathPrefix	When true, rustc remaps the (/nix/store) source paths to /sources to reduce the number of dependencies in the closure. Default: true
cargoTestCommands	The commands to run in the checkPhase. Do not forget to set doCheck. The argument must be a function modifying the default value. Default: [ ''cargo $cargo_options test $cargo_test_options'' ]
cargoTestOptions	Options passed to cargo test, i.e. cargo test <OPTS>. These options can be accessed during the build through the environment variable cargo_test_options. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ "$cargo_release" ''-j "$NIX_BUILD_CORES"'' ]
cargoClippyOptions	Options passed to cargo clippy, i.e. cargo clippy -- <OPTS>. These options can be accessed during the build through the environment variable cargo_clippy_options. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ "-D warnings" ]
cargoFmtOptions	Options passed to cargo fmt, i.e. cargo fmt -- <OPTS>. These options can be accessed during the build through the environment variable cargo_fmt_options. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ "--check" ]
nativeBuildInputs	Extra nativeBuildInputs to all derivations. Default: []
buildInputs	Extra buildInputs to all derivations. Default: []
cargoOptions	Options passed to all cargo commands, i.e. cargo <OPTS> .... These options can be accessed during the build through the environment variable cargo_options. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ ]
doDoc	When true, cargo doc is run and a new output doc is generated. Default: false
cargoDocCommands	The commands to run in the docPhase. Do not forget to set doDoc. The argument must be a function modifying the default value. Default: [ ''cargo $cargo_options doc $cargo_doc_options'' ]
cargoDocOptions	Options passed to cargo doc, i.e. cargo doc <OPTS>. These options can be accessed during the build through the environment variable cargo_doc_options. Note: these values are not (shell) escaped, meaning that you can use environment variables but must be careful when introducing e.g. spaces. The argument must be a function modifying the default value. Default: [ "--offline" "$cargo_release" ''-j "$NIX_BUILD_CORES"'' ]
release	When true, all cargo builds are run with --release. The environment variable cargo_release is set to --release iff this option is set. Default: true
override	An override for all derivations involved in the build. Default: (x: x)
overrideMain	An override for the top-level (last, main) derivation. If both override and overrideMain are specified, both will be applied to the top-level derivation. Default: (x: x)
singleStep	When true, no intermediary (dependency-only) build is run. Enabling singleStep greatly reduces the incrementality of the builds. Default: false
copyBins	When true, the resulting binaries are copied to $out/bin. Note: this relies on cargo's --message-format argument, set in the default cargoBuildOptions. Default: true
copyLibs	When true, the resulting binaries are copied to $out/lib. Note: this relies on cargo's --message-format argument, set in the default cargoBuildOptions. Default: false
copyBinsFilter	A jq filter for selecting which build artifacts to release. This is run on cargo's --message-format JSON output. The value is written to the cargo_bins_jq_filter variable. Default: ''select(.reason == "compiler-artifact" and .executable != null and .profile.test == false)''
copyLibsFilter	A jq filter for selecting which build artifacts to release. This is run on cargo's --message-format JSON output. The value is written to the cargo_libs_jq_filter variable. Default: `''select(.reason == "compiler-artifact" and ((.target.kind
copyDocsToSeparateOutput	When true, the documentation is generated in a different output, doc. Default: true
doDocFail	When true, the build fails if the documentation step fails; otherwise the failure is ignored. Default: false
removeReferencesToSrcFromDocs	When true, references to the nix store are removed from the generated documentation. Default: true
compressTarget	When true, the build output of intermediary builds is compressed with Zstandard. This reduces the size of closures. Default: true
copyTarget	When true, the target/ directory is copied to $out. Default: false
postInstall	Optional hook to run after the compilation is done; inside this script, $out/bin contains compiled Rust binaries. Useful if your application needs e.g. custom environment variables, in which case you can simply run wrapProgram $out/bin/your-app-name in here. Default: false
usePureFromTOML	Whether to use the fromTOML built-in or not. When set to false the python package remarshal is used instead (in a derivation) and the JSON output is read with builtins.fromJSON. This is a workaround for old versions of Nix. May be used safely from Nix 2.3 onwards where all bugs in builtins.fromTOML seem to have been fixed. Default: true
mode	What to do when building the derivation. Either build, check, test, fmt or clippy. When set to something other than build, no binaries are generated. Default: "build"
autoCrateSpecificOverrides	Whether to automatically apply crate-specific overrides, mainly additional buildInputs for dependencies. For example, if you use the openssl crate, pkgs.pkg-config and pkgs.openssl are automatically added as buildInputs. Default: true

Note on overrideAttrs

When you call buildPackage, Naersk internally builds two derivations: one that compiles all of your application's dependencies and then another one that compiles just your application.

It's done this way to improve compilation speed when you build your program for the second time etc., because then if only your application's code has changed (and Cargo.toml & Cargo.lock stayed the same), Naersk doesn't have to rebuild your dependencies.

This mechanism has a shortcoming, though - in particular, you shouldn't use overrideAttrs to inject something into the build environment:

{ pkgs, naersk, ... }:

let
  app = naersk.buildPackage {
    src = ./.;
  };

in
app.overrideAttrs (p: {
  buildInputs = p.buildInputs + [ pkgs.cmake ];
  SOME_ENV_VAR = "yes";
})

... because that will inject it only into the app-derivation, leaving it inaccessible for your dependencies to use.

Instead, you should pass the parameters directly into the buildPackage invocation:

{ pkgs, naersk, ... }:

naersk.buildPackage {
  src = ./.;
  buildInputs = [ pkgs.cmake ];
  SOME_ENV_VAR = "yes";
}

... or use override, if the names conflict with something already reserved by Naersk:

{ pkgs, naersk, ... }:

naersk.buildPackage {
  src = ./.;

  override = p: {
    # ...
  };
}

... or, if you really have to call overrideAttrs on the final derivation, you should disable the incremental-compilation mechanism:

{ pkgs, naersk, ... }:

let
  app = naersk.buildPackage {
    src = ./.;
    singleStep = true; # here
  };

in
app.overrideAttrs (p: {
  buildInputs = p.buildInputs + [ pkgs.cmake ];
})

(it's just an optimization so there's no harm in disabling it, Naersk should produce the same binary anyway.)

Examples

See: ./examples.

Tips & Tricks

Building a particular example

If you want to build only a particular example, use:

naersk.buildPackage {
  pname = "your-example-name";
  src = ./.;

  overrideMain = old: {
    preConfigure = ''
      cargo_build_options="$cargo_build_options --example your-example-name"
    '';
  };
}

Using CMake

If your application uses CMake, the build process might fail, saying:

CMake Error: The current CMakeCache.txt directory ... is different than the directory ... where CMakeCache.txt was created.

You can fix this problem by removing stale CMakeCache.txt files before the build:

naersk.buildPackage {
  # ...

  preBuild = ''
    find \
        -name CMakeCache.txt \
        -exec rm {} \;
  '';
}

(context)