embassy-executor-macros fails to compile on the latest Rust Nightly.

[danclive]

see: https://github.com/esp-rs/esp-hal/actions/runs/8342745449/job/22831570036#step:7:609

   Compiling examples v0.0.0 (/home/runner/work/esp-hal/esp-hal/examples)
error: concrete type differs from previous defining opaque type use
  --> src/bin/embassy_usb_serial_jtag.rs:27:1
   |
27 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `writer::Fut`, got `impl Future<Output = ()>`
   |
note: previous use here
  --> src/bin/embassy_usb_serial_jtag.rs:27:1
   |
27 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)

error: concrete type differs from previous defining opaque type use
  --> src/bin/embassy_usb_serial_jtag.rs:47:1
   |
47 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `reader::Fut`, got `impl Future<Output = ()>`
   |
note: previous use here
  --> src/bin/embassy_usb_serial_jtag.rs:47:1
   |
47 | #[embassy_executor::task]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: this error originates in the attribute macro `embassy_executor::task` (in Nightly builds, run with -Z macro-backtrace for more info)

[danclive]

This may be due to the recent Rust Nightly having a destructive impact on embassy-executor-macros.

embassy/embassy-executor-macros/src/macros/task.rs

Lines 93 to 101 in ea25112

	#[cfg(feature = "nightly")]
	let mut task_outer: ItemFn = parse_quote! {
	#visibility fn #task_ident(#fargs) -> ::embassy_executor::SpawnToken<impl Sized> {
	type Fut = impl ::core::future::Future + 'static;
	const POOL_SIZE: usize = #pool_size;
	static POOL: ::embassy_executor::raw::TaskPool<Fut, POOL_SIZE> = ::embassy_executor::raw::TaskPool::new();
	unsafe { POOL._spawn_async_fn(move || #task_inner_ident(#(#full_args,)*)) }
	}
	};

[jessebraham]

I understand that the stated policy here is that only the nightly version in the rust-toolchain.toml file is officially supported, but how are HAL developers expected to accommodate this? This is a pretty rigid restriction that I'm not really comfortable applying to our HAL.

[Dirbaio]

You can use nightly but not enable the nightly feature in embassy-executor. This'll make it use the task arena which works on stable, so it's not subject to the nightly breakages. With this you can choose any nightly version that works best for you.

I still have to look into this particular breakage and update it to work on newer nightlies. Perhaps merging #2574.

[Dirbaio]

seems a rust regression to me. Filed rust-lang/rust#122775

Seems #2574 is not affected

[Dirbaio]

fixed in #2574