rustup default doesn't show proper warning when architecture is not compatible

[bombless]

Fresh install rustup on my Windows Subsystem for Linux, choose stable-x86_64-apple-darwin toolchain
after installation, run rustc it reports ~/.rustup/toolchains/stable-x86_64-apple-darwin/bin/rustc: 1: Syntax error: "(" unexpected

Or if you choose stable-x86_64-pc-windows-gnu, run rustc after installation,
it reports error: the 'rustc' binary, normally provided by the 'rustc' component, is not applicable to the 'stable-x86_64-pc-windows-gnu' toolchain

[ehuss]

I think there may be some confusion here. There are two concepts in rustup, the toolchain host, and the standard library targets. It looks like you may have installed toolchains for other hosts, which won't run. You only need to install the toolchain for the host you are running on (so on WSL, it would be stable-x86_64-unknown-linux-gnu). To cross compile, you only need to install the standard library target (rustup target add x86_64-pc-windows-gnu). There is more information at https://rust-lang.github.io/rustup/cross-compilation.html about how to install targets, and https://rust-lang.github.io/rustup/concepts/index.html for more on the different concepts in rustup.

Just beware that cross compiling from linux to windows or macos is not particularly easy. This recent blogpost contains an overview of how to cross-compile to windows.

[bombless]

Thank you! I'll have a try a few hours later when I can reach my machine.

[bombless]

rustup run nightly-x86_64-unknown-linux-gnu cargo run --target=x86_64-pc-windows-gnu seems to do the job.

But I still wonder if it is considerable that we change rustup default a little bit so it can warn incompatible architecture

[workingjubilee]

That would be a rustup bug. Could this issue be transferred?

[ChrisDenton]

Attempting to transferr to rust-lang/rustup since this is an issue with the rustup tool...

@rustbot transfer rustup

[rami3l]

FWIW we do emit this warning for rustup toolchain install:

rustup/src/cli/rustup_mode.rs

Lines 820 to 825 in 4207838

	error!("DEPRECATED: future versions of rustup will require --force-non-host to install a non-host toolchain.");
	warn!("toolchain '{name}' may not be able to run on this system.");
	warn!(
	"If you meant to build software to target that platform, perhaps try `rustup target add {}` instead?",
	target_triple.to_string()
	);

> uname -mrs
Darwin 23.5.0 arm64

> rustup toolchain install stable-unknown-linux-gnu --profile=minimal
error: DEPRECATED: future versions of rustup will require --force-non-host to install a non-host toolchain.
warn: toolchain 'stable-unknown-linux-gnu' may not be able to run on this system.
warn: If you meant to build software to target that platform, perhaps try `rustup target add aarch64-unknown-linux-gnu` instead?
info: syncing channel updates for 'stable-aarch64-unknown-linux-gnu'
info: latest update on 2024-07-25, rust version 1.80.0 (051478957 2024-07-21)
info: downloading component 'cargo'
info: downloading component 'rust-std'
^C⏎                           

... it could be that this is not covered by rustup default somehow. So adding the same warning to that path should address this issue.

[rami3l]

rustup/src/cli/rustup_mode.rs

Lines 703 to 706 in 4207838

	async fn default_(
	cfg: &Cfg<'_>,
	toolchain: Option<MaybeResolvableToolchainName>,
	) -> Result<utils::ExitCode> {

... calls:

rustup/src/toolchain/distributable.rs

Line 362 in 4207838

pub async fn install_if_not_installed(

... so it looks like extracting the warning to a separate function and call it at the beginning of install_if_not_installed() above will do.

However, this function clashes with Cfg::ensure_installed, so it's better to unify them. I'll have a look later...