depot/third_party/nixpkgs/doc/languages-frameworks/rust.section.md

Rust

To install the rust compiler and cargo put

{
  environment.systemPackages = [
    rustc
    cargo
  ];
}

into your configuration.nix or bring them into scope with nix-shell -p rustc cargo.

For other versions such as daily builds (beta and nightly), use either rustup from nixpkgs (which will manage the rust installation in your home directory), or use community maintained Rust toolchains.

buildRustPackage: Compiling Rust applications with Cargo

Rust applications are packaged by using the buildRustPackage helper from rustPlatform:

{ lib, fetchFromGitHub, rustPlatform }:

rustPlatform.buildRustPackage rec {
  pname = "ripgrep";
  version = "12.1.1";

  src = fetchFromGitHub {
    owner = "BurntSushi";
    repo = pname;
    rev = version;
    hash = "sha256-+s5RBC3XSgb8omTbUNLywZnP6jSxZBKSS1BmXOjRF8M=";
  };

  cargoHash = "sha256-jtBw4ahSl88L0iuCXxQgZVm1EcboWRJMNtjxLVTtzts=";

  meta = {
    description = "Fast line-oriented regex search tool, similar to ag and ack";
    homepage = "https://github.com/BurntSushi/ripgrep";
    license = lib.licenses.unlicense;
    maintainers = [ ];
  };
}

buildRustPackage requires a cargoHash attribute, computed over all crate sources of this package.

::: {.warning} cargoSha256 is already deprecated, and is subject to removal in favor of cargoHash which supports SRI hashes.

If you are still using cargoSha256, you can simply replace it with cargoHash and recompute the hash, or convert the original sha256 to SRI hash using nix-hash --to-sri --type sha256 "<original sha256>". :::

{
  cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";
}

Exception: If the application has cargo git dependencies, the cargoHash approach will not work, and you will need to copy the Cargo.lock file of the application to nixpkgs and continue with the next section for specifying the options of the cargoLock section.

Both types of hashes are permitted when contributing to nixpkgs. The Cargo hash is obtained by inserting a fake checksum into the expression and building the package once. The correct checksum can then be taken from the failed build. A fake hash can be used for cargoHash as follows:

{
  cargoHash = lib.fakeHash;
}

Per the instructions in the Cargo Book best practices guide, Rust applications should always commit the Cargo.lock file in git to ensure a reproducible build. However, a few packages do not, and Nix depends on this file, so if it is missing you can use cargoPatches to apply it in the patchPhase. Consider sending a PR upstream with a note to the maintainer describing why it's important to include in the application.

The fetcher will verify that the Cargo.lock file is in sync with the src attribute, and fail the build if not. It will also will compress the vendor directory into a tar.gz archive.

The tarball with vendored dependencies contains a directory with the package's name, which is normally composed of pname and version. This means that the vendored dependencies hash (cargoHash) is dependent on the package name and version. The cargoDepsName attribute can be used to use another name for the directory of vendored dependencies. For example, the hash can be made invariant to the version by setting cargoDepsName to pname:

rustPlatform.buildRustPackage rec {
  pname = "broot";
  version = "1.2.0";

  src = fetchCrate {
    inherit pname version;
    hash = "sha256-aDQA4A5mScX9or3Lyiv/5GyAehidnpKKE0grhbP1Ctc=";
  };

  cargoHash = "sha256-tbrTbutUs5aPSV+yE0IBUZAAytgmZV7Eqxia7g+9zRs=";
  cargoDepsName = pname;

  # ...
}

Importing a Cargo.lock file

Using a vendored hash (cargoHash) is tedious when using buildRustPackage within a project, since it requires that the hash is updated after every change to Cargo.lock. Therefore, buildRustPackage also supports vendoring dependencies directly from a Cargo.lock file using the cargoLock argument. For example:

rustPlatform.buildRustPackage {
  pname = "myproject";
  version = "1.0.0";

  cargoLock = {
    lockFile = ./Cargo.lock;
  };

  # ...
}

This will retrieve the dependencies using fixed-output derivations from the specified lockfile.

One caveat is that Cargo.lock cannot be patched in the patchPhase because it runs after the dependencies have already been fetched. If you need to patch or generate the lockfile you can alternatively set cargoLock.lockFileContents to a string of its contents:

rustPlatform.buildRustPackage {
  pname = "myproject";
  version = "1.0.0";

  cargoLock = let
    fixupLockFile = path: f (builtins.readFile path);
  in {
    lockFileContents = fixupLockFile ./Cargo.lock;
  };

  # ...
}

Note that setting cargoLock.lockFile or cargoLock.lockFileContents doesn't add a Cargo.lock to your src, and a Cargo.lock is still required to build a rust package. A simple fix is to use:

{
  postPatch = ''
    ln -s ${./Cargo.lock} Cargo.lock
  '';
}

The output hash of each dependency that uses a git source must be specified in the outputHashes attribute. For example:

rustPlatform.buildRustPackage rec {
  pname = "myproject";
  version = "1.0.0";

  cargoLock = {
    lockFile = ./Cargo.lock;
    outputHashes = {
      "finalfusion-0.14.0" = "17f4bsdzpcshwh74w5z119xjy2if6l2wgyjy56v621skr2r8y904";
    };
  };

  # ...
}

If you do not specify an output hash for a git dependency, building the package will fail and inform you of which crate needs to be added. To find the correct hash, you can first use lib.fakeSha256 or lib.fakeHash as a stub hash. Building the package (and thus the vendored dependencies) will then inform you of the correct hash.

For usage outside nixpkgs, allowBuiltinFetchGit could be used to avoid having to specify outputHashes. For example:

rustPlatform.buildRustPackage rec {
  pname = "myproject";
  version = "1.0.0";

  cargoLock = {
    lockFile = ./Cargo.lock;
    allowBuiltinFetchGit = true;
  };

  # ...
}

Cargo features

You can disable default features using buildNoDefaultFeatures, and extra features can be added with buildFeatures.

If you want to use different features for check phase, you can use checkNoDefaultFeatures and checkFeatures. They are only passed to cargo test and not cargo build. If left unset, they default to buildNoDefaultFeatures and buildFeatures.

For example:

rustPlatform.buildRustPackage rec {
  pname = "myproject";
  version = "1.0.0";

  buildNoDefaultFeatures = true;
  buildFeatures = [ "color" "net" ];

  # disable network features in tests
  checkFeatures = [ "color" ];

  # ...
}

Cross compilation

By default, Rust packages are compiled for the host platform, just like any other package is. The --target passed to rust tools is computed from this. By default, it takes the stdenv.hostPlatform.config and replaces components where they are known to differ. But there are ways to customize the argument:

• To choose a different target by name, define stdenv.hostPlatform.rust.rustcTarget as that name (a string), and that name will be used instead.

  For example:

  import <nixpkgs> {
    crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
      rust.rustcTarget = "thumbv7em-none-eabi";
    };
  }
  

  will result in:

  --target thumbv7em-none-eabi
  

• To pass a completely custom target, define stdenv.hostPlatform.rust.rustcTarget with its name, and stdenv.hostPlatform.rust.platform with the value. The value will be serialized to JSON in a file called ${stdenv.hostPlatform.rust.rustcTarget}.json, and the path of that file will be used instead.

  For example:

  import <nixpkgs> {
    crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
      rust.rustcTarget = "thumb-crazy";
      rust.platform = { foo = ""; bar = ""; };
    };
  }
  

  will result in:

  --target /nix/store/asdfasdfsadf-thumb-crazy.json # contains {"foo":"","bar":""}
  

Note that currently custom targets aren't compiled with std, so cargo test will fail. This can be ignored by adding doCheck = false; to your derivation.

Running package tests

When using buildRustPackage, the checkPhase is enabled by default and runs cargo test on the package to build. To make sure that we don't compile the sources twice and to actually test the artifacts that will be used at runtime, the tests will be ran in the release mode by default.

However, in some cases the test-suite of a package doesn't work properly in the release mode. For these situations, the mode for checkPhase can be changed like so:

rustPlatform.buildRustPackage {
  /* ... */
  checkType = "debug";
}

Please note that the code will be compiled twice here: once in release mode for the buildPhase, and again in debug mode for the checkPhase.

Test flags, e.g., --package foo, can be passed to cargo test via the cargoTestFlags attribute.

Another attribute, called checkFlags, is used to pass arguments to the test binary itself, as stated here.

Tests relying on the structure of the target/ directory

Some tests may rely on the structure of the target/ directory. Those tests are likely to fail because we use cargo --target during the build. This means that the artifacts are stored in target/<architecture>/release/, rather than in target/release/.

This can only be worked around by patching the affected tests accordingly.

Disabling package-tests

In some instances, it may be necessary to disable testing altogether (with doCheck = false;):

• If no tests exist -- the checkPhase should be explicitly disabled to skip unnecessary build steps to speed up the build.
• If tests are highly impure (e.g. due to network usage).

There will obviously be some corner-cases not listed above where it's sensible to disable tests. The above are just guidelines, and exceptions may be granted on a case-by-case basis.

However, please check if it's possible to disable a problematic subset of the test suite and leave a comment explaining your reasoning.

This can be achieved with --skip in checkFlags:

rustPlatform.buildRustPackage {
  /* ... */
  checkFlags = [
    # reason for disabling test
    "--skip=example::tests:example_test"
  ];
}

Using cargo-nextest

Tests can be run with cargo-nextest by setting useNextest = true. The same options still apply, but nextest accepts a different set of arguments and the settings might need to be adapted to be compatible with cargo-nextest.

rustPlatform.buildRustPackage {
  /* ... */
  useNextest = true;
}

Setting test-threads

buildRustPackage will use parallel test threads by default, sometimes it may be necessary to disable this so the tests run consecutively.

rustPlatform.buildRustPackage {
  /* ... */
  dontUseCargoParallelTests = true;
}

Building a package in debug mode

By default, buildRustPackage will use release mode for builds. If a package should be built in debug mode, it can be configured like so:

rustPlatform.buildRustPackage {
  /* ... */
  buildType = "debug";
}

In this scenario, the checkPhase will be ran in debug mode as well.

Custom build/install-procedures

Some packages may use custom scripts for building/installing, e.g. with a Makefile. In these cases, it's recommended to override the buildPhase/installPhase/checkPhase.

Otherwise, some steps may fail because of the modified directory structure of target/.

Building a crate with an absent or out-of-date Cargo.lock file

buildRustPackage needs a Cargo.lock file to get all dependencies in the source code in a reproducible way. If it is missing or out-of-date one can use the cargoPatches attribute to update or add it.

rustPlatform.buildRustPackage rec {
  # ...
  cargoPatches = [
    # a patch file to add/update Cargo.lock in the source code
    ./add-Cargo.lock.patch
  ];
}

Compiling non-Rust packages that include Rust code

Several non-Rust packages incorporate Rust code for performance- or security-sensitive parts. rustPlatform exposes several functions and hooks that can be used to integrate Cargo in non-Rust packages.

Vendoring of dependencies

Since network access is not allowed in sandboxed builds, Rust crate dependencies need to be retrieved using a fetcher. rustPlatform provides the fetchCargoTarball fetcher, which vendors all dependencies of a crate. For example, given a source path src containing Cargo.toml and Cargo.lock, fetchCargoTarball can be used as follows:

{
  cargoDeps = rustPlatform.fetchCargoTarball {
    inherit src;
    hash = "sha256-BoHIN/519Top1NUBjpB/oEMqi86Omt3zTQcXFWqrek0=";
  };
}

The src attribute is required, as well as a hash specified through one of the hash attribute. The following optional attributes can also be used:

• name: the name that is used for the dependencies tarball. If name is not specified, then the name cargo-deps will be used.
• sourceRoot: when the Cargo.lock/Cargo.toml are in a subdirectory, sourceRoot specifies the relative path to these files.
• patches: patches to apply before vendoring. This is useful when the Cargo.lock/Cargo.toml files need to be patched before vendoring.

If a Cargo.lock file is available, you can alternatively use the importCargoLock function. In contrast to fetchCargoTarball, this function does not require a hash (unless git dependencies are used) and fetches every dependency as a separate fixed-output derivation. importCargoLock can be used as follows:

{
  cargoDeps = rustPlatform.importCargoLock {
    lockFile = ./Cargo.lock;
  };
}

If the Cargo.lock file includes git dependencies, then their output hashes need to be specified since they are not available through the lock file. For example:

{
  cargoDeps = rustPlatform.importCargoLock {
    lockFile = ./Cargo.lock;
    outputHashes = {
      "rand-0.8.3" = "0ya2hia3cn31qa8894s3av2s8j5bjwb6yq92k0jsnlx7jid0jwqa";
    };
  };
}

If you do not specify an output hash for a git dependency, building cargoDeps will fail and inform you of which crate needs to be added. To find the correct hash, you can first use lib.fakeSha256 or lib.fakeHash as a stub hash. Building cargoDeps will then inform you of the correct hash.

Hooks

rustPlatform provides the following hooks to automate Cargo builds:

• cargoSetupHook: configure Cargo to use dependencies vendored through fetchCargoTarball. This hook uses the cargoDeps environment variable to find the vendored dependencies. If a project already vendors its dependencies, the variable cargoVendorDir can be used instead. When the Cargo.toml/Cargo.lock files are not in sourceRoot, then the optional cargoRoot is used to specify the Cargo root directory relative to sourceRoot.
• cargoBuildHook: use Cargo to build a crate. If the crate to be built is a crate in e.g. a Cargo workspace, the relative path to the crate to build can be set through the optional buildAndTestSubdir environment variable. Features can be specified with cargoBuildNoDefaultFeatures and cargoBuildFeatures. Additional Cargo build flags can be passed through cargoBuildFlags.
• maturinBuildHook: use Maturin to build a Python wheel. Similar to cargoBuildHook, the optional variable buildAndTestSubdir can be used to build a crate in a Cargo workspace. Additional Maturin flags can be passed through maturinBuildFlags.
• cargoCheckHook: run tests using Cargo. The build type for checks can be set using cargoCheckType. Features can be specified with cargoCheckNoDefaultFeatures and cargoCheckFeatures. Additional flags can be passed to the tests using checkFlags and checkFlagsArray. By default, tests are run in parallel. This can be disabled by setting dontUseCargoParallelTests.
• cargoNextestHook: run tests using cargo-nextest. The same options for cargoCheckHook also applies to cargoNextestHook.
• cargoInstallHook: install binaries and static/shared libraries that were built using cargoBuildHook.
• bindgenHook: for crates which use bindgen as a build dependency, lets bindgen find libclang and libclang find the libraries in buildInputs.

Examples

Python package using setuptools-rust

For Python packages using setuptools-rust, you can use fetchCargoTarball and cargoSetupHook to retrieve and set up Cargo dependencies. The build itself is then performed by buildPythonPackage.

The following example outlines how the tokenizers Python package is built. Since the Python package is in the source/bindings/python directory of the tokenizers project's source archive, we use sourceRoot to point the tooling to this directory:

{ fetchFromGitHub
, buildPythonPackage
, cargo
, rustPlatform
, rustc
, setuptools-rust
}:

buildPythonPackage rec {
  pname = "tokenizers";
  version = "0.10.0";

  src = fetchFromGitHub {
    owner = "huggingface";
    repo = pname;
    rev = "python-v${version}";
    hash = "sha256-rQ2hRV52naEf6PvRsWVCTN7B1oXAQGmnpJw4iIdhamw=";
  };

  cargoDeps = rustPlatform.fetchCargoTarball {
    inherit pname version src sourceRoot;
    hash = "sha256-miW//pnOmww2i6SOGbkrAIdc/JMDT4FJLqdMFojZeoY=";
  };

  sourceRoot = "${src.name}/bindings/python";

  nativeBuildInputs = [
    cargo
    rustPlatform.cargoSetupHook
    rustc
    setuptools-rust
  ];

  # ...
}

In some projects, the Rust crate is not in the main Python source directory. In such cases, the cargoRoot attribute can be used to specify the crate's directory relative to sourceRoot. In the following example, the crate is in src/rust, as specified in the cargoRoot attribute. Note that we also need to specify the correct path for fetchCargoTarball.

{ buildPythonPackage
, fetchPypi
, rustPlatform
, setuptools-rust
, openssl
}:

buildPythonPackage rec {
  pname = "cryptography";
  version = "3.4.2"; # Also update the hash in vectors.nix

  src = fetchPypi {
    inherit pname version;
    hash = "sha256-xGDilsjLOnls3MfVbGKnj80KCUCczZxlis5PmHzpNcQ=";
  };

  cargoDeps = rustPlatform.fetchCargoTarball {
    inherit pname version src;
    sourceRoot = "${pname}-${version}/${cargoRoot}";
    hash = "sha256-PS562W4L1NimqDV2H0jl5vYhL08H9est/pbIxSdYVfo=";
  };

  cargoRoot = "src/rust";

  # ...
}

Python package using maturin

Python packages that use Maturin can be built with fetchCargoTarball, cargoSetupHook, and maturinBuildHook. For example, the following (partial) derivation builds the retworkx Python package. fetchCargoTarball and cargoSetupHook are used to fetch and set up the crate dependencies. maturinBuildHook is used to perform the build.

{ lib
, buildPythonPackage
, rustPlatform
, fetchFromGitHub
}:

buildPythonPackage rec {
  pname = "retworkx";
  version = "0.6.0";
  pyproject = true;

  src = fetchFromGitHub {
    owner = "Qiskit";
    repo = "retworkx";
    rev = version;
    hash = "sha256-11n30ldg3y3y6qxg3hbj837pnbwjkqw3nxq6frds647mmmprrd20=";
  };

  cargoDeps = rustPlatform.fetchCargoTarball {
    inherit pname version src;
    hash = "sha256-heOBK8qi2nuc/Ib+I/vLzZ1fUUD/G/KTw9d7M4Hz5O0=";
  };

  nativeBuildInputs = with rustPlatform; [ cargoSetupHook maturinBuildHook ];

  # ...
}

Rust package built with meson

Some projects, especially GNOME applications, are built with the Meson Build System instead of calling Cargo directly. Using rustPlatform.buildRustPackage may successfully build the main program, but related files will be missing. Instead, you need to set up Cargo dependencies with fetchCargoTarball and cargoSetupHook and leave the rest to Meson. rust and cargo are still needed in nativeBuildInputs for Meson to use.

{ lib
, stdenv
, fetchFromGitLab
, meson
, ninja
, pkg-config
, rustPlatform
, rustc
, cargo
, wrapGAppsHook4
, blueprint-compiler
, libadwaita
, libsecret
, tracker
}:

stdenv.mkDerivation rec {
  pname = "health";
  version = "0.95.0";

  src = fetchFromGitLab {
    domain = "gitlab.gnome.org";
    owner = "World";
    repo = "health";
    rev = version;
    hash = "sha256-PrNPprSS98yN8b8yw2G6hzTSaoE65VbsM3q7FVB4mds=";
  };

  cargoDeps = rustPlatform.fetchCargoTarball {
    inherit pname version src;
    hash = "sha256-8fa3fa+sFi5H+49B5sr2vYPkp9C9s6CcE0zv4xB8gww=";
  };

  nativeBuildInputs = [
    meson
    ninja
    pkg-config
    rustPlatform.cargoSetupHook
    rustc
    cargo
    wrapGAppsHook4
    blueprint-compiler
  ];

  buildInputs = [
    libadwaita
    libsecret
    tracker
  ];

  # ...
}

buildRustCrate: Compiling Rust crates using Nix instead of Cargo

Simple operation

When run, cargo build produces a file called Cargo.lock, containing pinned versions of all dependencies. Nixpkgs contains a tool called crate2Nix (nix-shell -p crate2nix), which can be used to turn a Cargo.lock into a Nix expression. That Nix expression calls rustc directly (hence bypassing Cargo), and can be used to compile a crate and all its dependencies.

See crate2nix's documentation for instructions on how to use it.

Handling external dependencies

Some crates require external libraries. For crates from crates.io, such libraries can be specified in defaultCrateOverrides package in nixpkgs itself.

Starting from that file, one can add more overrides, to add features or build inputs by overriding the hello crate in a separate file.

with import <nixpkgs> {};
((import ./hello.nix).hello {}).override {
  crateOverrides = defaultCrateOverrides // {
    hello = attrs: { buildInputs = [ openssl ]; };
  };
}

Here, crateOverrides is expected to be a attribute set, where the key is the crate name without version number and the value a function. The function gets all attributes passed to buildRustCrate as first argument and returns a set that contains all attribute that should be overwritten.

For more complicated cases, such as when parts of the crate's derivation depend on the crate's version, the attrs argument of the override above can be read, as in the following example, which patches the derivation:

with import <nixpkgs> {};
((import ./hello.nix).hello {}).override {
  crateOverrides = defaultCrateOverrides // {
    hello = attrs: lib.optionalAttrs (lib.versionAtLeast attrs.version "1.0")  {
      postPatch = ''
        substituteInPlace lib/zoneinfo.rs \
          --replace-fail "/usr/share/zoneinfo" "${tzdata}/share/zoneinfo"
      '';
    };
  };
}

Another situation is when we want to override a nested dependency. This actually works in the exact same way, since the crateOverrides parameter is forwarded to the crate's dependencies. For instance, to override the build inputs for crate libc in the example above, where libc is a dependency of the main crate, we could do:

with import <nixpkgs> {};
((import hello.nix).hello {}).override {
  crateOverrides = defaultCrateOverrides // {
    libc = attrs: { buildInputs = []; };
  };
}

Options and phases configuration

Actually, the overrides introduced in the previous section are more general. A number of other parameters can be overridden:

• The version of rustc used to compile the crate:

  (hello {}).override { rust = pkgs.rust; }
  

• Whether to build in release mode or debug mode (release mode by default):

  (hello {}).override { release = false; }
  

• Whether to print the commands sent to rustc when building (equivalent to --verbose in cargo:

  (hello {}).override { verbose = false; }
  

• Extra arguments to be passed to rustc:

  (hello {}).override { extraRustcOpts = "-Z debuginfo=2"; }
  

• Phases, just like in any other derivation, can be specified using the following attributes: preUnpack, postUnpack, prePatch, patches, postPatch, preConfigure (in the case of a Rust crate, this is run before calling the "build" script), postConfigure (after the "build" script),preBuild, postBuild, preInstall and postInstall. As an example, here is how to create a new module before running the build script:

  (hello {}).override {
    preConfigure = ''
       echo "pub const PATH=\"${hi.out}\";" >> src/path.rs"
    '';
  }
  

Setting Up nix-shell

Oftentimes you want to develop code from within nix-shell. Unfortunately buildRustCrate does not support common nix-shell operations directly (see this issue) so we will use stdenv.mkDerivation instead.

Using the example hello project above, we want to do the following:

• Have access to cargo and rustc
• Have the openssl library available to a crate through it's normal compilation mechanism (pkg-config).

A typical shell.nix might look like:

with import <nixpkgs> {};

stdenv.mkDerivation {
  name = "rust-env";
  nativeBuildInputs = [
    rustc cargo

    # Example Build-time Additional Dependencies
    pkg-config
  ];
  buildInputs = [
    # Example Run-time Additional Dependencies
    openssl
  ];

  # Set Environment Variables
  RUST_BACKTRACE = 1;
}

You should now be able to run the following:

$ nix-shell --pure
$ cargo build
$ cargo test

Using community maintained Rust toolchains

::: {.note} The following projects cannot be used within Nixpkgs since Import From Derivation (IFD) is disallowed in Nixpkgs. To package things that require Rust nightly, RUSTC_BOOTSTRAP = true; can sometimes be used as a hack. :::

There are two community maintained approaches to Rust toolchain management:

• oxalica's Rust overlay
• fenix

Despite their names, both projects provides a similar set of packages and overlays under different APIs.

Oxalica's overlay allows you to select a particular Rust version without you providing a hash or a flake input, but comes with a larger git repository than fenix.

Fenix also provides rust-analyzer nightly in addition to the Rust toolchains.

Both oxalica's overlay and fenix better integrate with nix and cache optimizations. Because of this and ergonomics, either of those community projects should be preferred to the Mozilla's Rust overlay (nixpkgs-mozilla).

The following documentation demonstrates examples using fenix and oxalica's Rust overlay with nix-shell and building derivations. More advanced usages like flake usage are documented in their own repositories.

Using Rust nightly with nix-shell

Here is a simple shell.nix that provides Rust nightly (default profile) using fenix:

with import <nixpkgs> { };
let
  fenix = callPackage
    (fetchFromGitHub {
      owner = "nix-community";
      repo = "fenix";
      # commit from: 2023-03-03
      rev = "e2ea04982b892263c4d939f1cc3bf60a9c4deaa1";
      hash = "sha256-AsOim1A8KKtMWIxG+lXh5Q4P2bhOZjoUhFWJ1EuZNNk=";
    })
    { };
in
mkShell {
  name = "rust-env";
  nativeBuildInputs = [
    # Note: to use stable, just replace `default` with `stable`
    fenix.default.toolchain

    # Example Build-time Additional Dependencies
    pkg-config
  ];
  buildInputs = [
    # Example Run-time Additional Dependencies
    openssl
  ];

  # Set Environment Variables
  RUST_BACKTRACE = 1;
}

Save this to shell.nix, then run:

$ rustc --version
rustc 1.69.0-nightly (13471d3b2 2023-03-02)

To see that you are using nightly.

Oxalica's Rust overlay has more complete examples of shell.nix (and cross compilation) under its examples directory.

Using Rust nightly in a derivation with buildRustPackage

You can also use Rust nightly to build rust packages using makeRustPlatform. The below snippet demonstrates invoking buildRustPackage with a Rust toolchain from oxalica's overlay:

with import <nixpkgs>
{
  overlays = [
    (import (fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
  ];
};
let
  rustPlatform = makeRustPlatform {
    cargo = rust-bin.selectLatestNightlyWith (toolchain: toolchain.default);
    rustc = rust-bin.selectLatestNightlyWith (toolchain: toolchain.default);
  };
in

rustPlatform.buildRustPackage rec {
  pname = "ripgrep";
  version = "12.1.1";

  src = fetchFromGitHub {
    owner = "BurntSushi";
    repo = "ripgrep";
    rev = version;
    hash = "sha256-+s5RBC3XSgb8omTbUNLywZnP6jSxZBKSS1BmXOjRF8M=";
  };

  cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";

  doCheck = false;

  meta = {
    description = "Fast line-oriented regex search tool, similar to ag and ack";
    homepage = "https://github.com/BurntSushi/ripgrep";
    license = with lib.licenses; [ mit unlicense ];
    maintainers = with lib.maintainers; [];
  };
}

Follow the below steps to try that snippet.

1. save the above snippet as default.nix in that directory
2. cd into that directory and run nix-build

Fenix also has examples with buildRustPackage, crane, naersk, and cross compilation in its Examples section.

Using git bisect on the Rust compiler

Sometimes an upgrade of the Rust compiler (rustc) will break a downstream package. In these situations, being able to git bisect the rustc version history to find the offending commit is quite useful. Nixpkgs makes it easy to do this.

First, roll back your nixpkgs to a commit in which its rustc used the most recent one which doesn't have the problem. You'll need to do this because of rustc's extremely aggressive version-pinning.

Next, add the following overlay, updating the Rust version to the one in your rolled-back nixpkgs, and replacing /git/scratch/rust with the path into which you have git cloned the rustc git repository:

 (final: prev: /*lib.optionalAttrs prev.stdenv.targetPlatform.isAarch64*/ {
   rust_1_72 =
     lib.updateManyAttrsByPath [{
       path = [ "packages" "stable" ];
       update = old: old.overrideScope(final: prev: {
         rustc-unwrapped = prev.rustc-unwrapped.overrideAttrs (_: {
           src = lib.cleanSource /git/scratch/rust;
           # do *not* put passthru.isReleaseTarball=true here
         });
       });
     }]
       prev.rust_1_72;
 })

If the problem you're troubleshooting only manifests when cross-compiling you can uncomment the lib.optionalAttrs in the example above, and replace isAarch64 with the target that is having problems. This will speed up your bisect quite a bit, since the host compiler won't need to be rebuilt.

Now, you can start a git bisect in the directory where you checked out the rustc source code. It is recommended to select the endpoint commits by searching backwards from origin/master for the commits which added the release notes for the versions in question. If you set the endpoints to commits on the release branches (i.e. the release tags), git-bisect will often get confused by the complex merge-commit structures it will need to traverse.

The command loop you'll want to use for bisecting looks like this:

git bisect {good,bad}  # depending on result of last build
git submodule update --init
CARGO_NET_OFFLINE=false cargo vendor \
  --sync ./src/tools/cargo/Cargo.toml \
  --sync ./src/tools/rust-analyzer/Cargo.toml \
  --sync ./compiler/rustc_codegen_cranelift/Cargo.toml \
  --sync ./src/bootstrap/Cargo.toml
nix-build $NIXPKGS -A package-broken-by-rust-changes

The git submodule update --init and cargo vendor commands above require network access, so they can't be performed from within the rustc derivation, unfortunately.