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Docs: fix "building" documentation w.r.t. meson #12977

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Docs: fix "building" documentation w.r.t. meson #12977

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de96547
docs: update cross compilation section from autotools to meson
Mic92 Apr 9, 2025
dd8b578
docs/building: fix attribute for nix-cli-ccacheStdenv
Mic92 Apr 9, 2025
a7862eb
Update doc/manual/source/development/building.md
Mic92 Apr 14, 2025
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24 changes: 5 additions & 19 deletions doc/manual/source/development/building.md
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Expand Up @@ -195,28 +195,14 @@ Nix uses a string with the following format to identify the *system type* or *pl
<cpu>-<os>[-<abi>]
```

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)):
It is set when Nix is compiled for the given system, and based on the output of Meson's [`host_machine` information](https://mesonbuild.com/Reference-manual_builtin_host_machine.html)>

```
<cpu>-<vendor>-<os>[<version>][-<abi>]
```

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)):
When cross-compiling Nix with Meson, you need to specify a [cross-file](https://mesonbuild.com/Cross-compilation.html) using the `--cross-file` option. Cross-files define the target architecture and toolchain.
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Maybe we should point people to the cross flake outputs here (e.g. nix build .#nix-everything-riscv64-unknown-linux-gnu).

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Suggested change
When cross-compiling Nix with Meson, you need to specify a [cross-file](https://mesonbuild.com/Cross-compilation.html) using the `--cross-file` option. Cross-files define the target architecture and toolchain.
When cross-compiling Nix with Meson for local development, you need to specify a [cross-file](https://mesonbuild.com/Cross-compilation.html) using the `--cross-file` option. Cross-files define the target architecture and toolchain.
When cross-compiling Nix with Nix, Nixpkgs takes care of this for you.

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This section isn't really about cross compiling, so I'm not sure that we need to be entirely specific in this particular place, but it'd be good to catch a somewhat lost reader here. Doing all this is quite the detour if you're not doing it for local dev.


```
<cpu>-<vendor>[-<kernel>]-<os>
```

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:

| `config.guess` | Nix |
|----------------------------|---------------------|
| `amd64` | `x86_64` |
| `i*86` | `i686` |
| `arm6` | `arm6l` |
| `arm7` | `arm7l` |
| `linux-gnu*` | `linux` |
| `linux-musl*` | `linux` |
Comment on lines -206 to -219
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I think we should document how the system differs from Meson's defaults likewise? we have

host_machine.cpu_family() + '-' + host_machine.system()

currently, but I recall there was an issue pointing out this cases a regression with Power CPUs, and responded that a PR making a special case would be welcome. That is the sort of thing we'd document here.

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#12769 this is the issue I was thinking of.


## Compilation environments

Expand All @@ -230,18 +216,18 @@ Nix can be compiled using multiple environments:
To build with one of those environments, you can use

```console
$ nix build .#nix-ccacheStdenv
$ nix build .#nix-cli-ccacheStdenv
```

for flake-enabled Nix, or

```console
$ nix-build --attr nix-ccacheStdenv
$ nix-build --attr nix-cli-ccacheStdenv
```

for classic Nix.

You can use any of the other supported environments in place of `nix-ccacheStdenv`.
You can use any of the other supported environments in place of `nix-cli-ccacheStdenv`.

## Editor integration

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