ashpd regression

[compiler-errors]

Not yet minimized

https://crater-reports.s3.amazonaws.com/pr-133502-1/try%23fa8e241660363f48d64b66b05eea58c93ab828fb/reg/rfd-0.15.3/log.txt

[INFO] [stdout] error: lifetime may not live long enough
[INFO] [stdout]    --> /opt/rustwide/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/ashpd-0.11.0/src/proxy.rs:258:5
[INFO] [stdout]     |
[INFO] [stdout] 35  |   impl<'a> Proxy<'a> {
[INFO] [stdout]     |        -- lifetime `'a` defined here
[INFO] [stdout] ...
[INFO] [stdout] 258 | /     pub(crate) async fn signal<I>(&self, name: &'static str) -> Result<impl Stream<Item = I>, Error>
[INFO] [stdout] 259 | |     where
[INFO] [stdout] 260 | |         I: for<'de> Deserialize<'de> + Type + Debug,
[INFO] [stdout]     | |____________________________________________________^ opaque type requires that `'a` must outlive `'static`
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] error: lifetime may not live long enough
[INFO] [stdout]    --> /opt/rustwide/cargo-home/registry/src/index.crates.io-1949cf8c6b5b557f/ashpd-0.11.0/src/proxy.rs:258:5
[INFO] [stdout]     |
[INFO] [stdout] 258 |       pub(crate) async fn signal<I>(&self, name: &'static str) -> Result<impl Stream<Item = I>, Error>
[INFO] [stdout]     |       ^                             - let's call the lifetime of this reference `'1`
[INFO] [stdout]     |  _____|
[INFO] [stdout]     | |
[INFO] [stdout] 259 | |     where
[INFO] [stdout] 260 | |         I: for<'de> Deserialize<'de> + Type + Debug,
[INFO] [stdout]     | |____________________________________________________^ opaque type requires that `'1` must outlive `'static`
[INFO] [stdout]     |
[INFO] [stdout] help: to declare that `impl futures_util::Stream<Item = I>` captures data from argument `self`, you can add an explicit `'_` lifetime bound
[INFO] [stdout]     |
[INFO] [stdout] 258 |     pub(crate) async fn signal<I>(&self, name: &'static str) -> Result<impl Stream<Item = I> + '_, Error>
[INFO] [stdout]     |                                                                                              ++++
[INFO] [stdout] 
[INFO] [stdout] 
[INFO] [stdout] help: replace `'a` with `'static`

[compiler-errors]

This is due to the new opaque type changes, b/c it doesn't repro on master.

[compiler-errors]

Having not yet familiarized myself with the new opaque implementation, I would assume it's b/c some borrowck change is not taking opaque variance into account here.

[lcnr]

minimized

use std::future::Future;
fn test<'a>() -> impl Future<Output = impl Sized + use<>> + use<'a> {
    async {
        &()
    }
}

[lcnr]

trait Id {
    type This;
}
impl<T> Id for T {
    type This = T;
}

fn test<'a>() -> impl Id<This = impl Sized + use<>> + use<'a> {
    &()
}

got two member constraints 'unconstrained member ['a, 'static] and 'unconstrained member ['static]

The first member constraint currently adds 'unconstrained: 'a while the second then adds 'unconstrained: 'static. The impl on master only actually maps the member regions to the opaque definition after applying all member constraints, so the outer opaque then also sees that 'a has to be 'static.

My PR currently applies member constraints and then eagerly maps the hidden type to the definition site. So the outer opaque infers its hidden type as &'a () while the inner requires &'static (). This then causes us to equate 'a and 'static