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# Rust {#rust}
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To install the rust compiler and cargo put
```nix
environment.systemPackages = [
rustc
cargo
];
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```
into your `configuration.nix` or bring them into scope with `nix-shell -p rustc cargo`.
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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 a community maintained [Rust overlay](#using-community-rust-overlays).
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## Compiling Rust applications with Cargo {#compiling-rust-applications-with-cargo}
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Rust applications are packaged by using the `buildRustPackage` helper from `rustPlatform`:
```nix
{ lib, fetchFromGitHub, rustPlatform }:
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rustPlatform.buildRustPackage rec {
pname = "ripgrep";
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version = "12.1.1";
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src = fetchFromGitHub {
owner = "BurntSushi";
repo = pname;
rev = version;
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sha256 = "1hqps7l5qrjh9f914r5i6kmcz6f1yb951nv4lby0cjnp5l253kps";
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};
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cargoSha256 = "03wf9r2csi6jpa7v5sw5lpxkrk4wfzwmzx7k3991q3bdjzcwnnwp";
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meta = with lib; {
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description = "A fast line-oriented regex search tool, similar to ag and ack";
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homepage = "https://github.com/BurntSushi/ripgrep";
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license = licenses.unlicense;
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maintainers = [ maintainers.tailhook ];
};
}
```
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`buildRustPackage` requires either the `cargoSha256` or the
`cargoHash` attribute which is computed over all crate sources of this
package. `cargoHash256` is used for traditional Nix SHA-256 hashes,
such as the one in the example above. `cargoHash` should instead be
used for [SRI](https://www.w3.org/TR/SRI/) hashes. For example:
```nix
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cargoHash = "sha256-l1vL2ZdtDRxSGvP0X/l3nMw8+6WF67KPutJEzUROjg8=";
```
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
`cargoSha256` as follows:
```nix
cargoSha256 = lib.fakeSha256;
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```
For `cargoHash` you can use:
```nix
cargoHash = lib.fakeHash;
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```
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Per the instructions in the [Cargo Book](https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html)
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
(`cargoSha256`/`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`:
```nix
rustPlatform.buildRustPackage rec {
pname = "broot";
version = "1.2.0";
src = fetchCrate {
inherit pname version;
sha256 = "1mqaynrqaas82f5957lx31x80v74zwmwmjxxlbywajb61vh00d38";
};
cargoHash = "sha256-JmBZcDVYJaK1cK05cxx5BrnGWp4t8ca6FLUbvIot67s=";
cargoDepsName = pname;
# ...
}
```
### Importing a `Cargo.lock` file {#importing-a-cargo.lock-file}
Using `cargoSha256` or `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:
```nix
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:
```nix
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:
```nix
postPatch = ''
cp ${./Cargo.lock} Cargo.lock
'';
```
The output hash of each dependency that uses a git source must be
specified in the `outputHashes` attribute. For example:
```nix
rustPlatform.buildRustPackage rec {
pname = "myproject";
version = "1.0.0";
cargoLock = {
lockFile = ./Cargo.lock;
outputHashes = {
"finalfusion-0.14.0" = "17f4bsdzpcshwh74w5z119xjy2if6l2wgyjy56v621skr2r8y904";
};
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};
# ...
}
```
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.
### Cargo features {#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:
```nix
rustPlatform.buildRustPackage rec {
pname = "myproject";
version = "1.0.0";
buildNoDefaultFeatures = true;
buildFeatures = [ "color" "net" ];
# disable network features in tests
checkFeatures = [ "color" ];
# ...
}
```
### Cross compilation {#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.rustc.config` as that name (a string), and that
name will be used instead.
For example:
```nix
import <nixpkgs> {
crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
rustc.config = "thumbv7em-none-eabi";
};
}
```
will result in:
```shell
--target thumbv7em-none-eabi
```
- To pass a completely custom target, define
`stdenv.hostPlatform.rustc.config` with its name, and
`stdenv.hostPlatform.rustc.platform` with the value. The value will be
serialized to JSON in a file called
`${stdenv.hostPlatform.rustc.config}.json`, and the path of that file
will be used instead.
For example:
```nix
import <nixpkgs> {
crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
rustc.config = "thumb-crazy";
rustc.platform = { foo = ""; bar = ""; };
};
}
```
will result in:
```shell
--target /nix/store/asdfasdfsadf-thumb-crazy.json # contains {"foo":"","bar":""}
```
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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 {#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
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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:
```nix
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)[https://doc.rust-lang.org/cargo/commands/cargo-test.html].
#### Tests relying on the structure of the `target/` directory {#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/`](https://doc.rust-lang.org/cargo/guide/build-cache.html),
rather than in `target/release/`.
This can only be worked around by patching the affected tests accordingly.
#### Disabling package-tests {#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.
#### Setting `test-threads` {#setting-test-threads}
`buildRustPackage` will use parallel test threads by default,
sometimes it may be necessary to disable this so the tests run consecutively.
```nix
rustPlatform.buildRustPackage {
/* ... */
dontUseCargoParallelTests = true;
}
```
### Building a package in `debug` mode {#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:
```nix
rustPlatform.buildRustPackage {
/* ... */
buildType = "debug";
}
```
In this scenario, the `checkPhase` will be ran in `debug` mode as well.
### Custom `build`/`install`-procedures {#custom-buildinstall-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 {#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.
```nix
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 {#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 {#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:
```nix
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 `sha256` or `hash` attributes. 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 {#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](https://github.com/PyO3/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
`cargoCheckNoDefaultFeaatures` 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`.
* `cargoInstallHook`: install binaries and static/shared libraries
that were built using `cargoBuildHook`.
### Examples {#examples}
#### Python package using `setuptools-rust` {#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:
```nix
{ fetchFromGitHub
, buildPythonPackage
, rustPlatform
, setuptools-rust
}:
buildPythonPackage rec {
pname = "tokenizers";
version = "0.10.0";
src = fetchFromGitHub {
owner = "huggingface";
repo = pname;
rev = "python-v${version}";
hash = "sha256-rQ2hRV52naEf6PvRsWVCTN7B1oXAQGmnpJw4iIdhamw=";
};
cargoDeps = rustPlatform.fetchCargoTarball {
inherit src sourceRoot;
name = "${pname}-${version}";
hash = "sha256-BoHIN/519Top1NUBjpB/oEMqi86Omt3zTQcXFWqrek0=";
};
sourceRoot = "source/bindings/python";
nativeBuildInputs = [ setuptools-rust ] ++ (with rustPlatform; [
cargoSetupHook
rust.cargo
rust.rustc
]);
# ...
}
```
In some projects, the Rust crate is not in the main Python source
directory. In such cases, the `cargoRoot` attribute can be used to
specify the crate's directory relative to `sourceRoot`. In the
following example, the crate is in `src/rust`, as specified in the
`cargoRoot` attribute. Note that we also need to specify the correct
path for `fetchCargoTarball`.
```nix
{ buildPythonPackage
, fetchPypi
, rustPlatform
, setuptools-rust
, openssl
}:
buildPythonPackage rec {
pname = "cryptography";
version = "3.4.2"; # Also update the hash in vectors.nix
src = fetchPypi {
inherit pname version;
sha256 = "1i1mx5y9hkyfi9jrrkcw804hmkcglxi6rmf7vin7jfnbr2bf4q64";
};
cargoDeps = rustPlatform.fetchCargoTarball {
inherit src;
sourceRoot = "${pname}-${version}/${cargoRoot}";
name = "${pname}-${version}";
hash = "sha256-PS562W4L1NimqDV2H0jl5vYhL08H9est/pbIxSdYVfo=";
};
cargoRoot = "src/rust";
# ...
}
```
#### Python package using `maturin` {#python-package-using-maturin}
Python packages that use [Maturin](https://github.com/PyO3/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.
```nix
{ lib
, buildPythonPackage
, rustPlatform
, fetchFromGitHub
}:
buildPythonPackage rec {
pname = "retworkx";
version = "0.6.0";
src = fetchFromGitHub {
owner = "Qiskit";
repo = "retworkx";
rev = version;
sha256 = "11n30ldg3y3y6qxg3hbj837pnbwjkqw3nxq6frds647mmmprrd20";
};
cargoDeps = rustPlatform.fetchCargoTarball {
inherit src;
name = "${pname}-${version}";
hash = "sha256-heOBK8qi2nuc/Ib+I/vLzZ1fUUD/G/KTw9d7M4Hz5O0=";
};
format = "pyproject";
nativeBuildInputs = with rustPlatform; [ cargoSetupHook maturinBuildHook ];
# ...
}
```
## Compiling Rust crates using Nix instead of Cargo {#compiling-rust-crates-using-nix-instead-of-cargo}
### Simple operation {#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:
```ShellSession
$ 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:
```nix
2018-01-28 19:29:09 +00:00
# Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
{ stdenv, buildRustCrate, fetchgit }:
let kernel = stdenv.buildPlatform.parsed.kernel.name;
# ... (content skipped)
in
rec {
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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:
```nix
2018-01-28 19:29:09 +00:00
# Generated by carnix 0.6.5: carnix -o hello.nix --src ./. Cargo.lock --standalone
{ stdenv, buildRustCrate, fetchgit }:
let kernel = stdenv.buildPlatform.parsed.kernel.name;
# ... (content skipped)
in
rec {
2018-01-28 19:29:09 +00:00
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;
};
2018-01-28 19:29:09 +00:00
hello_0_1_0 = { features?(hello_0_1_0_features {}) }: hello_0_1_0_ {
dependencies = mapFeatures features ([ libc_0_2_36 ]);
};
2018-01-28 19:29:09 +00:00
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 {#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 separate file.
```nix
with import <nixpkgs> {};
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((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
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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:
```nix
with import <nixpkgs> {};
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((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" "${tzdata}/share/zoneinfo"
'';
};
};
}
```
Another situation is when we want to override a nested
dependency. This actually works in the exact same way, since the
`crateOverrides` parameter is forwarded to the crate's
dependencies. For instance, to override the build inputs for crate
`libc` in the example above, where `libc` is a dependency of the main
crate, we could do:
```nix
with import <nixpkgs> {};
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((import hello.nix).hello {}).override {
crateOverrides = defaultCrateOverrides // {
libc = attrs: { buildInputs = []; };
};
}
```
### Options and phases configuration {#options-and-phases-configuration}
Actually, the overrides introduced in the previous section are more
general. A number of other parameters can be overridden:
- The version of `rustc` used to compile the crate:
```nix
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(hello {}).override { rust = pkgs.rust; };
```
- Whether to build in release mode or debug mode (release mode by
default):
```nix
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(hello {}).override { release = false; };
```
- Whether to print the commands sent to `rustc` when building
(equivalent to `--verbose` in cargo:
```nix
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(hello {}).override { verbose = false; };
```
- Extra arguments to be passed to `rustc`:
```nix
(hello {}).override { extraRustcOpts = "-Z debuginfo=2"; };
```
- Phases, just like in any other derivation, can be specified using
the following attributes: `preUnpack`, `postUnpack`, `prePatch`,
`patches`, `postPatch`, `preConfigure` (in the case of a Rust crate,
this is run before calling the "build" script), `postConfigure`
(after the "build" script),`preBuild`, `postBuild`, `preInstall` and
`postInstall`. As an example, here is how to create a new module
before running the build script:
```nix
(hello {}).override {
preConfigure = ''
echo "pub const PATH=\"${hi.out}\";" >> src/path.rs"
'';
};
```
### Features {#features}
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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:
```nix
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(callPackage ./diesel.nix {}).diesel {
default = false;
postgres = true;
}
```
Where `diesel.nix` is the file generated by Carnix, as explained above.
## Setting Up `nix-shell` {#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:
```nix
with import <nixpkgs> {};
stdenv.mkDerivation {
name = "rust-env";
nativeBuildInputs = [
rustc cargo
# Example Build-time Additional Dependencies
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pkg-config
];
buildInputs = [
# Example Run-time Additional Dependencies
openssl
];
# Set Environment Variables
RUST_BACKTRACE = 1;
}
```
You should now be able to run the following:
```ShellSession
$ nix-shell --pure
$ cargo build
$ cargo test
```
### Controlling Rust Version Inside `nix-shell` {#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`
```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 = [
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# Note: to use stable, just replace `nightly` with `stable`
latest.rustChannels.nightly.rust
# Add some extra dependencies from `pkgs`
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pkg-config openssl
];
# Set Environment Variables
RUST_BACKTRACE = 1;
}
```
Now run:
```ShellSession
$ rustc --version
rustc 1.26.0-nightly (188e693b3 2018-03-26)
```
To see that you are using nightly.
## Using community Rust overlays {#using-community-rust-overlays}
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There are two community maintained approaches to Rust toolchain management:
- [oxalica's Rust overlay](https://github.com/oxalica/rust-overlay)
- [fenix](https://github.com/nix-community/fenix)
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Oxalica's overlay allows you to select a particular Rust version and components.
See [their documentation](https://github.com/oxalica/rust-overlay#rust-overlay) for more
detailed usage.
Fenix is an alternative to `rustup` and can also be used as an overlay.
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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`).
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### How to select a specific `rustc` and toolchain version {#how-to-select-a-specific-rustc-and-toolchain-version}
You can consume the oxalica overlay and use it to grab a specific Rust toolchain version.
Here is an example `shell.nix` showing how to grab the current stable toolchain:
```nix
{ pkgs ? import <nixpkgs> {
overlays = [
(import (fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
];
}
}:
pkgs.mkShell {
nativeBuildInputs = with pkgs; [
pkg-config
rust-bin.stable.latest.minimal
];
}
```
You can try this out by:
1. Saving that to `shell.nix`
2. Executing `nix-shell --pure --command 'rustc --version'`
As of writing, this prints out `rustc 1.56.0 (09c42c458 2021-10-18)`.
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### How to use an overlay toolchain in a derivation {#how-to-use-an-overlay-toolchain-in-a-derivation}
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You can also use an overlay's Rust toolchain with `buildRustPackage`.
The below snippet demonstrates invoking `buildRustPackage` with an oxalica overlay selected Rust toolchain:
```nix
with import <nixpkgs> {
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overlays = [
(import (fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
];
};
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rustPlatform.buildRustPackage rec {
pname = "ripgrep";
version = "12.1.1";
nativeBuildInputs = [
rust-bin.stable.latest.minimal
];
src = fetchFromGitHub {
owner = "BurntSushi";
repo = "ripgrep";
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rev = version;
sha256 = "1hqps7l5qrjh9f914r5i6kmcz6f1yb951nv4lby0cjnp5l253kps";
};
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cargoSha256 = "03wf9r2csi6jpa7v5sw5lpxkrk4wfzwmzx7k3991q3bdjzcwnnwp";
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meta = with 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 ];
};
}
```
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Follow the below steps to try that snippet.
1. create a new directory
1. save the above snippet as `default.nix` in that directory
1. cd into that directory and run `nix-build`
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### Rust overlay installation {#rust-overlay-installation}
You can use this overlay by either changing your local nixpkgs configuration,
or by adding the overlay declaratively in a nix expression, e.g. in `configuration.nix`.
For more information see [the manual on installing overlays](#sec-overlays-install).
### Declarative Rust overlay installation {#declarative-rust-overlay-installation}
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This snippet shows how to use oxalica's Rust overlay.
Add the following to your `configuration.nix`, `home-configuration.nix`, `shell.nix`, or similar:
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```nix
{ pkgs ? import <nixpkgs> {
overlays = [
(import (builtins.fetchTarball "https://github.com/oxalica/rust-overlay/archive/master.tar.gz"))
# Further overlays go here
];
};
};
```
Note that this will fetch the latest overlay version when rebuilding your system.