ICE in github build

[xoviat]

See below:

https://github.com/akiles/embassy/runs/1699580405?check_suite_focus=true

[hellow554]

Reduced to only use the task proc-macro:

use embassy::executor::task;

#[task]
async fn run() {
    let a = Foo ;
}

It seems important, that Foo isn't defined, if I define a struct Foo, the ICE goes away.

[hellow554]

searched nightlies: from nightly-2020-06-01 to nightly-2021-01-01
regressed nightly: nightly-2020-10-27
searched commits: from 4760b8f to fd54259
regressed commit: b9a94c9

bisected with cargo-bisect-rustc v0.6.0

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc 2020-06-01 --regress ice --access github -- check

---

I'm pretty sure that #78324 isn't at fault here, but instead it just uncovers the problem.

[hellow554]

MCVE:

#![feature(type_alias_impl_trait)]

use std::future::Future;

pub struct Task<F: Future>(F);
impl<F: Future> Task<F> {
    fn new() -> Self {
        todo!()
    }
    fn spawn(&self, _: impl FnOnce() -> F) {
        todo!()
    }
}

fn main() {
    async fn cb() {
        let a = Foo;
    }

    type F = impl Future;
    static POOL: Task<F> = Task::new();
    Task::spawn(&POOL, || cb());
}

[jonas-schievink]

Panic location:

rust/compiler/rustc_middle/src/ty/mod.rs

Lines 3071 to 3073 in a4f022e

	pub fn generator_layout(self, def_id: DefId) -> &'tcx GeneratorLayout<'tcx> {
	self.optimized_mir(def_id).generator_layout.as_ref().unwrap()
	}