config.rust: update references from rustc

`rustc.config` is called `rust.rustcTarget` now, and
`{rustc -> rust}.platform`.

This is the new way (tm), and is preferred since
#271707 -
though the documentation still is outdated, and some expressions in
nixpkgs were using the old interface.

This updates both.

doc/languages-frameworks/rust.section.md

@@ -254,15 +254,15 @@ 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
+ `stdenv.hostPlatform.rust.rustcTarget` 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";
+ rust.rustcTarget = "thumbv7em-none-eabi";
  };
  }
  ```
@@ -274,19 +274,19 @@ where they are known to differ. But there are ways to customize the argument:
  ```
 
  - 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
+ `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
- `${stdenv.hostPlatform.rustc.config}.json`, and the path of that file
+ `${stdenv.hostPlatform.rust.rustcTarget}.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 = ""; };
+ rust.rustcTarget = "thumb-crazy";
+ rust.platform = { foo = ""; bar = ""; };
  };
  }
  ```

lib/systems/examples.nix

@@ -59,15 +59,15 @@ rec {
 
  armv7a-android-prebuilt = {
  config = "armv7a-unknown-linux-androideabi";
- rustc.config = "armv7-linux-androideabi";
+ rust.rustcTarget = "armv7-linux-androideabi";
  sdkVer = "28";
  ndkVer = "24";
  useAndroidPrebuilt = true;
  } // platforms.armv7a-android;
 
  aarch64-android-prebuilt = {
  config = "aarch64-unknown-linux-android";
- rustc.config = "aarch64-linux-android";
+ rust.rustcTarget = "aarch64-linux-android";
  sdkVer = "28";
  ndkVer = "24";
  useAndroidPrebuilt = true;
@@ -207,7 +207,7 @@ rec {
  aarch64-embedded = {
  config = "aarch64-none-elf";
  libc = "newlib";
- rustc.config = "aarch64-unknown-none";
+ rust.rustcTarget = "aarch64-unknown-none";
  };
 
  aarch64be-embedded = {

pkgs/applications/virtualization/rust-hypervisor-firmware/default.nix

@@ -17,8 +17,8 @@ let
  cross = import ../../../.. {
  system = hostPlatform.system;
  crossSystem = lib.systems.examples."${arch}-embedded" // {
- rustc.config = "${arch}-unknown-none";
- rustc.platform = lib.importJSON target;
+ rust.rustcTarget = "${arch}-unknown-none";
+ rust.platform = lib.importJSON target;
  };
  };