---
title: Rust
author: Matthias Beyer
date: 2017-03-05
---
# Rust
To install the rust compiler and cargo put
```
rustc
cargo
```
into the `environment.systemPackages` or bring them into
scope with `nix-shell -p rustc cargo`.
For daily builds (beta and nightly) use either rustup from
nixpkgs or use the [Rust nightlies
overlay](#using-the-rust-nightlies-overlay).
## Compiling Rust applications with Cargo
Rust applications are packaged by using the `buildRustPackage` helper from `rustPlatform`:
```
rustPlatform.buildRustPackage rec {
pname = "ripgrep";
version = "11.0.2";
src = fetchFromGitHub {
owner = "BurntSushi";
repo = pname;
rev = version;
sha256 = "1iga3320mgi7m853la55xip514a3chqsdi1a1rwv25lr9b1p7vd3";
};
cargoSha256 = "17ldqr3asrdcsh4l29m3b5r37r5d0b3npq1lrgjmxb6vlx6a36qh";
verifyCargoDeps = true;
meta = with stdenv.lib; {
description = "A fast line-oriented regex search tool, similar to ag and ack";
homepage = https://github.com/BurntSushi/ripgrep;
license = licenses.unlicense;
maintainers = [ maintainers.tailhook ];
platforms = platforms.all;
};
}
```
`buildRustPackage` requires a `cargoSha256` attribute which is computed over
all crate sources of this package. Currently it is obtained by inserting a
fake checksum into the expression and building the package once. The correct
checksum can be then take from the failed build.
When the `Cargo.lock`, provided by upstream, is not in sync with the
`Cargo.toml`, it is possible to use `cargoPatches` to update it. All patches
added in `cargoPatches` will also be prepended to the patches in `patches` at
build-time.
When `verifyCargoDeps` is set to `true`, the build will also verify that the
`cargoSha256` is not out of date by comparing the `Cargo.lock` file in both the
`cargoDeps` and `src`. Note that this option changes the value of `cargoSha256`
since it also copies the `Cargo.lock` in it. To avoid breaking
backward-compatibility this option is not enabled by default but hopefully will
be in the future.
### Building a crate for a different target
To build your crate with a different cargo `--target` simply specify the `target` attribute:
```nix
pkgs.rustPlatform.buildRustPackage {
(...)
target = "x86_64-fortanix-unknown-sgx";
}
```
## 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 `carnix` (`nix-env -iA nixos.carnix`), 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. Here is
an example for a minimal `hello` crate:
$ cargo new hello
$ cd hello
$ cargo build
Compiling hello v0.1.0 (file:///tmp/hello)
Finished dev [unoptimized + debuginfo] target(s) in 0.20 secs
$ carnix -o hello.nix --src ./. Cargo.lock --standalone
$ nix-build hello.nix -A hello_0_1_0
Now, the file produced by the call to `carnix`, called `hello.nix`, looks like:
```
# Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
{ lib, stdenv, buildRustCrate, fetchgit }:
let kernel = stdenv.buildPlatform.parsed.kernel.name;
# ... (content skipped)
in
rec {
hello = f: hello_0_1_0 { features = hello_0_1_0_features { hello_0_1_0 = f; }; };
hello_0_1_0_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
crateName = "hello";
version = "0.1.0";
authors = [ "pe@pijul.org <pe@pijul.org>" ];
src = ./.;
inherit dependencies buildDependencies features;
};
hello_0_1_0 = { features?(hello_0_1_0_features {}) }: hello_0_1_0_ {};
hello_0_1_0_features = f: updateFeatures f (rec {
hello_0_1_0.default = (f.hello_0_1_0.default or true);
}) [ ];
}
```
In particular, note that the argument given as `--src` is copied
verbatim to the source. If we look at a more complicated
dependencies, for instance by adding a single line `libc="*"` to our
`Cargo.toml`, we first need to run `cargo build` to update the
`Cargo.lock`. Then, `carnix` needs to be run again, and produces the
following nix file:
```
# Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
{ lib, stdenv, buildRustCrate, fetchgit }:
let kernel = stdenv.buildPlatform.parsed.kernel.name;
# ... (content skipped)
in
rec {
hello = f: hello_0_1_0 { features = hello_0_1_0_features { hello_0_1_0 = f; }; };
hello_0_1_0_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
crateName = "hello";
version = "0.1.0";
authors = [ "pe@pijul.org <pe@pijul.org>" ];
src = ./.;
inherit dependencies buildDependencies features;
};
libc_0_2_36_ = { dependencies?[], buildDependencies?[], features?[] }: buildRustCrate {
crateName = "libc";
version = "0.2.36";
authors = [ "The Rust Project Developers" ];
sha256 = "01633h4yfqm0s302fm0dlba469bx8y6cs4nqc8bqrmjqxfxn515l";
inherit dependencies buildDependencies features;
};
hello_0_1_0 = { features?(hello_0_1_0_features {}) }: hello_0_1_0_ {
dependencies = mapFeatures features ([ libc_0_2_36 ]);
};
hello_0_1_0_features = f: updateFeatures f (rec {
hello_0_1_0.default = (f.hello_0_1_0.default or true);
libc_0_2_36.default = true;
}) [ libc_0_2_36_features ];
libc_0_2_36 = { features?(libc_0_2_36_features {}) }: libc_0_2_36_ {
features = mkFeatures (features.libc_0_2_36 or {});
};
libc_0_2_36_features = f: updateFeatures f (rec {
libc_0_2_36.default = (f.libc_0_2_36.default or true);
libc_0_2_36.use_std =
(f.libc_0_2_36.use_std or false) ||
(f.libc_0_2_36.default or false) ||
(libc_0_2_36.default or false);
}) [];
}
```
Here, the `libc` crate has no `src` attribute, so `buildRustCrate`
will fetch it from [crates.io](https://crates.io). A `sha256`
attribute is still needed for Nix purity.
### Handling external dependencies
Some crates require external libraries. For crates from
[crates.io](https://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 seperate 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 "/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"
'';
};
```
### Features
One can also supply features switches. For example, if we want to
compile `diesel_cli` only with the `postgres` feature, and no default
features, we would write:
```
(callPackage ./diesel.nix {}).diesel {
default = false;
postgres = true;
}
```
Where `diesel.nix` is the file generated by Carnix, as explained above.
## 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](https://github.com/NixOS/nixpkgs/issues/37945))
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
pkgconfig
];
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
```
### Controlling Rust Version Inside `nix-shell`
To control your rust version (i.e. use nightly) from within `shell.nix` (or
other nix expressions) you can use the following `shell.nix`
```
# Latest Nightly
with import <nixpkgs> {};
let src = fetchFromGitHub {
owner = "mozilla";
repo = "nixpkgs-mozilla";
# commit from: 2019-05-15
rev = "9f35c4b09fd44a77227e79ff0c1b4b6a69dff533";
sha256 = "18h0nvh55b5an4gmlgfbvwbyqj91bklf1zymis6lbdh75571qaz0";
};
in
with import "${src.out}/rust-overlay.nix" pkgs pkgs;
stdenv.mkDerivation {
name = "rust-env";
buildInputs = [
# Note: to use use stable, just replace `nightly` with `stable`
latest.rustChannels.nightly.rust
# Add some extra dependencies from `pkgs`
pkgconfig openssl
];
# Set Environment Variables
RUST_BACKTRACE = 1;
}
```
Now run:
```
$ rustc --version
rustc 1.26.0-nightly (188e693b3 2018-03-26)
```
To see that you are using nightly.
## Using the Rust nightlies overlay
Mozilla provides an overlay for nixpkgs to bring a nightly version of Rust into scope.
This overlay can _also_ be used to install recent unstable or stable versions
of Rust, if desired.
To use this overlay, clone
[nixpkgs-mozilla](https://github.com/mozilla/nixpkgs-mozilla),
and create a symbolic link to the file
[rust-overlay.nix](https://github.com/mozilla/nixpkgs-mozilla/blob/master/rust-overlay.nix)
in the `~/.config/nixpkgs/overlays` directory.
$ git clone https://github.com/mozilla/nixpkgs-mozilla.git
$ mkdir -p ~/.config/nixpkgs/overlays
$ ln -s $(pwd)/nixpkgs-mozilla/rust-overlay.nix ~/.config/nixpkgs/overlays/rust-overlay.nix
The latest version can be installed with the following command:
$ nix-env -Ai nixos.latest.rustChannels.stable.rust
Or using the attribute with nix-shell:
$ nix-shell -p nixos.latest.rustChannels.stable.rust
To install the beta or nightly channel, "stable" should be substituted by
"nightly" or "beta", or
use the function provided by this overlay to pull a version based on a
build date.
The overlay automatically updates itself as it uses the same source as
[rustup](https://www.rustup.rs/).