fix: update FindRust to work with rustup v1.28.0

[rami3l]

Closes #590 by applying the following mapping:

Variable \ Rustup ver.	v1.27.1	v1.28.0
$_TOOLCHAIN_OVERRIDE	(override)	(active)
$_TOOLCHAIN_DEFAULT	(default)	(default) or (active, default)

Rationale

Corrosion would like to find out the path for the active toolchain via rustup toolchain list --verbose from the toolchains marked (override) and/or (default): if (override) is present, then it's active, otherwise (default) would be active:

corrosion/cmake/FindRust.cmake

Lines 423 to 428 in b88ec09

	if (NOT DEFINED Rust_TOOLCHAIN)
	if (NOT DEFINED _TOOLCHAIN_OVERRIDE)
	set(_TOOLCHAIN_SELECTED "${_TOOLCHAIN_DEFAULT}")
	else()
	set(_TOOLCHAIN_SELECTED "${_TOOLCHAIN_OVERRIDE}")
	endif()

In rustup v1.28.0 beta (or rust-lang/rustup#3225 to be more precise), we have recognized that this output format has become a common source of confusion among users in determining the active toolchain, so we now mark the active toolchain with (active) instead. Unfortunately, this has broken corrosion's parsing logic.

Verification

Changes verified locally via the following interactions:

> rustup --version
rustup 1.28.0 :: 1.27.1+544 (7ccf717e6 2024-12-23)
...

> rustup toolchain list --verbose # The "default" state.
stable-aarch64-apple-darwin (active, default) ...
nightly-aarch64-apple-darwin ...
nightly-2023-09-30-aarch64-apple-darwin ...

> rustup +nightly toolchain list --verbose # The "override" state.
stable-aarch64-apple-darwin (default) ...
nightly-aarch64-apple-darwin (active) ...
nightly-2023-09-30-aarch64-apple-darwin ...

> cmake -S. -Bbuild -URust_TOOLCHAIN
-- Rust Toolchain: stable-aarch64-apple-darwin
-- Rust Target: aarch64-apple-darwin
-- Found Rust: SOME/.rustup/toolchains/stable-aarch64-apple-darwin/bin/rustc (found version "1.83.0")
-- Configuring done (0.2s)
-- Generating done (0.1s)
...

> RUSTUP_TOOLCHAIN=nightly cmake -S. -Bbuild -URust_TOOLCHAIN
-- Rust Toolchain: nightly-aarch64-apple-darwin
-- Rust Target: aarch64-apple-darwin
-- Found Rust: SOME/.rustup/toolchains/nightly-aarch64-apple-darwin/bin/rustc (found version "1.85.0")
-- Configuring done (0.2s)
-- Generating done (0.1s)
...

Concerns

• I'm not sure why -URust_TOOLCHAIN is required to make this work. Has it been somehow set to "" by something?
• Am I doing the verification right? If not, how should I properly verify this change?

[jschwe]

The intended way to specify a toolchain is by running cmake -S. -Bbuild -DRust_TOOLCHAIN=xxx. It'st best to rm -rf build to start from a clean build dir when testing.
RUSTUP_TOOLCHAIN=nightly working is a bonus, but most users include corrosion from CMake files, so configuring corrosion via CMake variables is the standard case.

[jschwe]

LGTM, I'll be travelling today so I won't be able to make a new release today

[rami3l]

@jschwe Thanks for the quick response! The CI error does look weird to me as it doesn't seem related to my change, is this a pre-existing issue?

[jschwe]

Yeah, the CI issue with installing cbindgen is unrelated. It's popped up recently and I haven't had time to investigate what changed and why it's only failing on Linux.

[jschwe]

@rami3l Thanks for the PR! Please do note, that I still need to do a backport to the v0.5 branch and cut a new release.