mirror of
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This is needed to avoid this https://github.com/mesonbuild/meson/issues/13774 when we go back to making our subproject directory `src`.
293 lines
9.4 KiB
Markdown
293 lines
9.4 KiB
Markdown
# Building Nix
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This section provides some notes on how to start hacking on Nix.
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To get the latest version of Nix from GitHub:
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```console
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$ git clone https://github.com/NixOS/nix.git
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$ cd nix
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```
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> **Note**
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>
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> The following instructions assume you already have some version of Nix installed locally, so that you can use it to set up the development environment.
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> If you don't have it installed, follow the [installation instructions](../installation/index.md).
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To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
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```console
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$ nix-shell
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```
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To get a shell with one of the other [supported compilation environments](#compilation-environments):
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```console
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$ nix-shell --attr devShells.x86_64-linux.native-clangStdenvPackages
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```
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> **Note**
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>
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> You can use `native-ccacheStdenvPackages` to drastically improve rebuild time.
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> By default, [ccache](https://ccache.dev) keeps artifacts in `~/.cache/ccache/`.
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To build Nix itself in this shell:
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```console
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[nix-shell]$ mesonFlags+=" --prefix=$(pwd)/outputs/out"
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[nix-shell]$ dontAddPrefix=1 mesonConfigurePhase
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[nix-shell]$ ninjaBuildPhase
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```
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To test it:
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```console
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[nix-shell]$ mesonCheckPhase
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```
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To install it in `$(pwd)/outputs`:
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```console
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[nix-shell]$ ninjaInstallPhase
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[nix-shell]$ ./outputs/out/bin/nix --version
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nix (Nix) 2.12
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```
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To build a release version of Nix for the current operating system and CPU architecture:
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```console
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$ nix-build
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```
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You can also build Nix for one of the [supported platforms](#platforms).
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## Building Nix with flakes
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This section assumes you are using Nix with the [`flakes`] and [`nix-command`] experimental features enabled.
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[`flakes`]: @docroot@/development/experimental-features.md#xp-feature-flakes
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[`nix-command`]: @docroot@/development/experimental-features.md#xp-nix-command
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To build all dependencies and start a shell in which all environment variables are set up so that those dependencies can be found:
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```console
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$ nix develop
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```
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This shell also adds `./outputs/bin/nix` to your `$PATH` so you can run `nix` immediately after building it.
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To get a shell with one of the other [supported compilation environments](#compilation-environments):
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```console
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$ nix develop .#native-clangStdenvPackages
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```
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> **Note**
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>
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> Use `ccacheStdenv` to drastically improve rebuild time.
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> By default, [ccache](https://ccache.dev) keeps artifacts in `~/.cache/ccache/`.
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To build Nix itself in this shell:
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```console
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[nix-shell]$ mesonConfigurePhase
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[nix-shell]$ ninjaBuildPhase
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```
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To test it:
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```console
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[nix-shell]$ mesonCheckPhase
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```
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To install it in `$(pwd)/outputs`:
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```console
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[nix-shell]$ ninjaInstallPhase
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[nix-shell]$ nix --version
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nix (Nix) 2.12
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```
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For more information on running and filtering tests, see
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[`testing.md`](./testing.md).
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To build a release version of Nix for the current operating system and CPU architecture:
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```console
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$ nix build
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```
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You can also build Nix for one of the [supported platforms](#platforms).
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## Platforms
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Nix can be built for various platforms, as specified in [`flake.nix`]:
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[`flake.nix`]: https://github.com/nixos/nix/blob/master/flake.nix
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- `x86_64-linux`
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- `x86_64-darwin`
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- `i686-linux`
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- `aarch64-linux`
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- `aarch64-darwin`
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- `armv6l-linux`
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- `armv7l-linux`
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- `riscv64-linux`
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In order to build Nix for a different platform than the one you're currently
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on, you need a way for your current Nix installation to build code for that
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platform. Common solutions include [remote build machines] and [binary format emulation]
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(only supported on NixOS).
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[remote builders]: @docroot@/language/derivations.md#attr-builder
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[binary format emulation]: https://nixos.org/manual/nixos/stable/options.html#opt-boot.binfmt.emulatedSystems
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Given such a setup, executing the build only requires selecting the respective attribute.
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For example, to compile for `aarch64-linux`:
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```console
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$ nix-build --attr packages.aarch64-linux.default
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```
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or for Nix with the [`flakes`] and [`nix-command`] experimental features enabled:
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```console
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$ nix build .#packages.aarch64-linux.default
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```
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Cross-compiled builds are available for:
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- `armv6l-linux`
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- `armv7l-linux`
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- `riscv64-linux`
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Add more [system types](#system-type) to `crossSystems` in `flake.nix` to bootstrap Nix on unsupported platforms.
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### Building for multiple platforms at once
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It is useful to perform multiple cross and native builds on the same source tree,
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for example to ensure that better support for one platform doesn't break the build for another.
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Meson thankfully makes this very easy by confining all build products to the build directory --- one simple shares the source directory between multiple build directories, each of which contains the build for Nix to a different platform.
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Nixpkgs's `mesonConfigurePhase` always chooses `build` in the current directory as the name and location of the build.
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This makes having multiple build directories slightly more inconvenient.
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The good news is that Meson/Ninja seem to cope well with relocating the build directory after it is created.
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Here's how to do that
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1. Configure as usual
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```bash
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mesonConfigurePhase
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```
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2. Rename the build directory
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```bash
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cd .. # since `mesonConfigurePhase` cd'd inside
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mv build build-linux # or whatever name we want
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cd build-linux
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```
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3. Build as usual
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```bash
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ninjaBuildPhase
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```
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> **N.B.**
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> [`nixpkgs#335818`](https://github.com/NixOS/nixpkgs/issues/335818) tracks giving `mesonConfigurePhase` proper support for custom build directories.
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> When it is fixed, we can simplify these instructions and then remove this notice.
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## System type
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Nix uses a string with the following format to identify the *system type* or *platform* it runs on:
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```
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<cpu>-<os>[-<abi>]
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```
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It is set when Nix is compiled for the given system, and based on the output of [`config.guess`](https://github.com/nixos/nix/blob/master/config/config.guess) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.guess)):
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```
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<cpu>-<vendor>-<os>[<version>][-<abi>]
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```
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When Nix is built such that `./configure` is passed any of the `--host`, `--build`, `--target` options, the value is based on the output of [`config.sub`](https://github.com/nixos/nix/blob/master/config/config.sub) ([upstream](https://git.savannah.gnu.org/cgit/config.git/tree/config.sub)):
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```
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<cpu>-<vendor>[-<kernel>]-<os>
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```
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For historic reasons and backward-compatibility, some CPU and OS identifiers are translated from the GNU Autotools naming convention in [`configure.ac`](https://github.com/nixos/nix/blob/master/configure.ac) as follows:
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| `config.guess` | Nix |
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|----------------------------|---------------------|
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| `amd64` | `x86_64` |
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| `i*86` | `i686` |
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| `arm6` | `arm6l` |
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| `arm7` | `arm7l` |
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| `linux-gnu*` | `linux` |
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| `linux-musl*` | `linux` |
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## Compilation environments
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Nix can be compiled using multiple environments:
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- `stdenv`: default;
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- `gccStdenv`: force the use of `gcc` compiler;
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- `clangStdenv`: force the use of `clang` compiler;
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- `ccacheStdenv`: enable [ccache], a compiler cache to speed up compilation.
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To build with one of those environments, you can use
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```console
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$ nix build .#nix-ccacheStdenv
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```
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for flake-enabled Nix, or
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```console
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$ nix-build --attr nix-ccacheStdenv
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```
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for classic Nix.
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You can use any of the other supported environments in place of `nix-ccacheStdenv`.
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## Editor integration
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The `clangd` LSP server is installed by default on the `clang`-based `devShell`s.
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See [supported compilation environments](#compilation-environments) and instructions how to set up a shell [with flakes](#nix-with-flakes) or in [classic Nix](#classic-nix).
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To use the LSP with your editor, you will want a `compile_commands.json` file telling `clangd` how we are compiling the code.
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Meson's configure always produces this inside the build directory.
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Configure your editor to use the `clangd` from the `.#native-clangStdenvPackages` shell. You can do that either by running it inside the development shell, or by using [nix-direnv](https://github.com/nix-community/nix-direnv) and [the appropriate editor plugin](https://github.com/direnv/direnv/wiki#editor-integration).
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> **Note**
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>
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> For some editors (e.g. Visual Studio Code), you may need to install a [special extension](https://open-vsx.org/extension/llvm-vs-code-extensions/vscode-clangd) for the editor to interact with `clangd`.
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> Some other editors (e.g. Emacs, Vim) need a plugin to support LSP servers in general (e.g. [lsp-mode](https://github.com/emacs-lsp/lsp-mode) for Emacs and [vim-lsp](https://github.com/prabirshrestha/vim-lsp) for vim).
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> Editor-specific setup is typically opinionated, so we will not cover it here in more detail.
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## Formatting and pre-commit hooks
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You may run the formatters as a one-off using:
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```console
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./maintainers/format.sh
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```
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If you'd like to run the formatters before every commit, install the hooks:
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```
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pre-commit-hooks-install
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```
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This installs [pre-commit](https://pre-commit.com) using [cachix/git-hooks.nix](https://github.com/cachix/git-hooks.nix).
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When making a commit, pay attention to the console output.
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If it fails, run `git add --patch` to approve the suggestions _and commit again_.
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To refresh pre-commit hook's config file, do the following:
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1. Exit the development shell and start it again by running `nix develop`.
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2. If you also use the pre-commit hook, also run `pre-commit-hooks-install` again.
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