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async fn in trait: ICE with 2 generic params in method #102310

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Dirbaio opened this issue Sep 26, 2022 · 3 comments · Fixed by #102334
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async fn in trait: ICE with 2 generic params in method #102310

Dirbaio opened this issue Sep 26, 2022 · 3 comments · Fixed by #102334
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C-bug Category: This is a bug. F-async_fn_in_trait Static async fn in traits I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.

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@Dirbaio
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Dirbaio commented Sep 26, 2022

playground

pub trait SpiDevice {
    async fn transaction<F, R>(&mut self);
}

impl SpiDevice for () {
    async fn transaction<F, R>(&mut self) {}
}

gives

error: internal compiler error: compiler/rustc_middle/src/ty/subst.rs:674:9: expected type for `R/#1` (R/1) but found Lifetime(ReFree(DefId(0:11 ~ embedded_hal_async[dae4]::spi::{impl#0}::transaction), BrNamed(DefId(0:16 ~ embedded_hal_async[dae4]::spi::SpiDevice::transaction::'_), '_))) when substituting, substs=[R, ReFree(DefId(0:11 ~ embedded_hal_async[dae4]::spi::{impl#0}::transaction), BrNamed(DefId(0:16 ~ embedded_hal_async[dae4]::spi::SpiDevice::transaction::'_), '_)), ReFree(DefId(0:11 ~ embedded_hal_async[dae4]::spi::{impl#0}::transaction), BrNamed(DefId(0:16 ~ embedded_hal_async[dae4]::spi::SpiDevice::transaction::'_), '_))]

full stack trace

happens with either

rustc 1.66.0-dev (21265dd)
1.66.0-nightly (2022-09-25 f5193a9)
@Dirbaio
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Dirbaio commented Sep 26, 2022

@rustbot label +F-async_fn_in_traits

@rustbot rustbot added the F-async_fn_in_trait Static async fn in traits label Sep 26, 2022
@Dirbaio Dirbaio mentioned this issue Sep 26, 2022
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@Rageking8
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@rustbot label +T-compiler +C-bug +I-ICE +requires-nightly

@Dirbaio Please use the ICE issue template for subsequent ICE issues. Thanks.

@rustbot rustbot added C-bug Category: This is a bug. I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 26, 2022
@compiler-errors compiler-errors mentioned this issue Sep 27, 2022
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@compiler-errors
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This is fixed by #102334

@bors bors closed this as completed in 8be3ce9 Oct 16, 2022
bors bot added a commit to rust-embedded/embedded-hal that referenced this issue Nov 23, 2022
@bors @Dirbaio
Merge #407
812471b 
407: async: switch to async-fn-in-traits, release v0.2.0-alpha.0 r=eldruin a=Dirbaio

Latest Rust nightlies have somewhat usable async-fn-in-trait support already! 🎉 

embassy-nrf updated here embassy-rs/embassy#974

Paprecuts encountered:

- there's this annoying error [playground](https://play.rust-lang.org/?version=nightly&mode=debug&edition=2021&gist=f04fca1f2a3d643c323fb49c05bd3ed3), workaround is to use the concrete type instead of `Self::Error`. This is a limitation of all `async fn`s, not just in traits, but it hits especially hard within traits, so I dunno if there's plans to improve it.

> `async fn` return type cannot contain a projection or `Self` that references lifetimes from a parent scope

- The SpiDevice trait ICEs, issue filed rust-lang/rust#102310
- default methods don't work, but there's a PR already rust-lang/rust#102308

Due to the last 2 I've left `SpiDevice` alone for now.

Co-authored-by: Dario Nieuwenhuis <[email protected]>
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Labels
C-bug Category: This is a bug. F-async_fn_in_trait Static async fn in traits I-ICE Issue: The compiler panicked, giving an Internal Compilation Error (ICE) ❄️ requires-nightly This issue requires a nightly compiler in some way. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue.
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Fix subst issues with return-position impl Trait in trait compiler-errors/rust
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@Dirbaio @compiler-errors @rustbot @Rageking8