Set nightly as the default toolchain in CI

[fitzgen]

So that random direct invocations of rustc or cargo in our CI scripts get the right version.

[abrown]

Not sure this worked?

[fitzgen]

Interesting. Any idea why the build script would be using 1.65.0 despite us specifying nightly as the default version (which is currently 1.68.0)?

From the build script output:

_CARGO=cargo 1.65.0 (4bc8f24d3 2022-10-20)

AFAICT, the CI action runs run-all.sh which does

    rustc build.rs
    ./build

in the wasmtime engine directory. That rustc and the cargo invocations inside the build script should all be using the rustup default version.

[fitzgen]

The action to install the rust toolchain is installing 1.68.0-nightly, so somehow the build script ends up getting a different one.

https://github.com/bytecodealliance/sightglass/actions/runs/3875774546/jobs/6608773907#step:3:35

  nightly-x86_64-unknown-linux-gnu unchanged - rustc 1.68.0-nightly (cc47b0699 2023-01-08)

[abrown]

Maybe something weird is going on with CI: I can see the task you linked to seems to have passed and the build environment that is emitted has the correct 1.68.0 version: https://github.com/bytecodealliance/sightglass/actions/runs/3875774546/jobs/6608773907#step:5:398. For the current failing task, though, it is back to 1.65.0 and it looks like the the rustup default nightly never happens: https://github.com/bytecodealliance/sightglass/actions/runs/3875774546/jobs/6608773907#step:5:398 (working) vs https://github.com/bytecodealliance/sightglass/actions/runs/3875774530/jobs/6608773021#step:3:17 (not working).