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doc/rust: Use rustcTargetSpec everywhere

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Cargo uses the basename of a JSON target specification in various places
to refer to targets, cc-rs parses the basename to grab target
information. There may be other examples where the basename is relevant.

Instead of fighting these existing conventions, let's just recommend
users provide a rustcTargetSpec, either as a standard name or as a
custom JSON file with the right basename
This commit is contained in:
dramforever 2025-09-27 22:16:22 +08:00
parent 60ac986e49
commit 8920a83327
1 changed files with 16 additions and 17 deletions
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33
doc/languages-frameworks/rust.section.md
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@ -254,7 +254,7 @@ 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
`stdenv.hostPlatform.rust.rustcTargetSpec` as that name (a string), and that
name will be used instead.
For example:
@ -262,7 +262,7 @@ where they are known to differ. But there are ways to customize the argument:
```nix
import <nixpkgs> {
crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
rust.rustcTarget = "thumbv7em-none-eabi";
rust.rustcTargetSpec = "thumbv7em-none-eabi";
};
}
```
@ -274,22 +274,24 @@ where they are known to differ. But there are ways to customize the argument:
```
- 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
`${stdenv.hostPlatform.rust.rustcTarget}.json`, and the path of that file
will be used instead.
`stdenv.hostPlatform.rust.rustcTargetSpec` with the path to the custom
target specification JSON file.
Note that some tools like Cargo and some crates like `cc` make use of the
file name of the target JSON. Therefore, do not use
`./path/to/target-spec.json` directly, because it will be renamed by Nix.
Instead, place it a directory and use `"${./path/to/dir}/target-spec.json"`.
The directory should contain only this one file, to avoid unrelated changes
causing unnecessary rebuilds.
For example:
```nix
import <nixpkgs> {
crossSystem = (import <nixpkgs/lib>).systems.examples.armhf-embedded // {
rust.rustcTarget = "thumb-crazy";
rust.platform = {
foo = "";
bar = "";
};
crossSystem = {
config = "mips64el-unknown-linux-gnuabi64";
# gcc = ...; # Config for C compiler omitted
rust.rustcTargetSpec = "${./rust}/mips64el_mips3-unknown-linux-gnuabi64.json";
};
}
```
@ -297,12 +299,9 @@ where they are known to differ. But there are ways to customize the argument:
will result in:
```shell
--target /nix/store/asdfasdfsadf-thumb-crazy.json # contains {"foo":"","bar":""}
--target /nix/store/...-rust/mips64el_mips3-unknown-linux-gnuabi64.json
```
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