regression: the type `(dyn Any + 'static)` may contain interior mutability

[BoxyUwU]

• https://crater-reports.s3.amazonaws.com/beta-1.79-2/beta-2024-05-11/gh/acfoltzer.wasm-async-main/log.txt

[INFO] [stdout] error[E0277]: the type `(dyn Any + 'static)` may contain interior mutability and a reference may not be safely transferrable across a catch_unwind boundary
[INFO] [stdout]   --> src/main.rs:13:1
[INFO] [stdout]    |
[INFO] [stdout] 13 | / lucet_hostcalls! {
[INFO] [stdout] 14 | |     #[no_mangle]
[INFO] [stdout] 15 | |     pub unsafe extern "C" fn two(&mut _vmctx,) -> *mut AssertUnwindSafe<Box<dyn Future<Output = u64>>> {
[INFO] [stdout] 16 | |         async fn body() -> u64 {

[lqd]

I'll need to re-check later but this seems to bisect to #123203 somehow.

[inquisitivecrystal]

I'll need to re-check later but this seems to bisect to #123203 somehow.

The UI test changes from that PR appear to back this up, as confusing as it is.

[lqd]

I'm not sure what's going on in that crate, if it built successfully by mistake, or how that PR interacts with it, so let's cc the PR author @jkarneges and reviewer @Amanieu for validation.

[lukas-code]

After #123203, Context no longer implements UnwindSafe and RefUnwindSafe, because the context now contains a &mut dyn Any which doesn't implement those traits. So this is an issue with the standard library and not the crate being built.

Repro: playground

use std::panic::UnwindSafe;
use std::task::Context;

fn unwind_safe<T: UnwindSafe>() {}

fn main() {
    unwind_safe::<Context<'_>>(); // test UnwindSafe
    unwind_safe::<&Context<'_>>(); // test RefUnwindSafe
}

@rustbot label -T-compiler +T-libs +S-has-mcve