regression: as_place unwrap None

[Mark-Simulacrum]

[INFO] [stderr] thread 'rustc' panicked at compiler/rustc_mir_build/src/build/expr/as_place.rs:253:31:
[INFO] [stderr] called `Option::unwrap()` on a `None` value

• https://crater-reports.s3.amazonaws.com/beta-1.73-1.2/beta-2023-09-10/gh/bonedaddy.ellidri/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.73-1.2/beta-2023-09-10/gh/edu-sync.edu-sync/log.txt
• https://crater-reports.s3.amazonaws.com/beta-1.73-1.2/beta-2023-09-10/gh/nevi-me.matter-oxide/log.txt

[matthiaskrgr]

Might be related to #110453

[apiraino]

I've tried the first 2 crates (bonedaddy.ellidri and edu-sync), they compile on the current stable fail to compile on beta and nightly.

Provisionally assigning P-high waiting for more investigation (Zulip discussion).

@rustbot label -I-prioritize +P-high +T-compiler

[apiraino]

bisected to commit 7e4f5ecde93e629a44ad3678059c5cd364791d27, where in this commit originates the issue:
Regression in rust-lang-ci@7e4f5ec i.e. rollup PR #113120

• Implement proposed API for proc_macro_span #111571 (Implement proposed API for proc_macro_span)
• Simplify computation of killed borrows #112236 (Simplify computation of killed borrows)
• More ImplSource nits #112867 (More ImplSource nits)
• add note for non-exhaustive matches with guards #113019 (add note for non-exhaustive matches with guards)
• Fix invalid HTML DIV tag used in HEAD #113094 (Fix invalid HTML DIV tag used in HEAD)
• add myself to review for t-types stuff #113111 (add myself to review for t-types stuff)

@rustbot label -e-needs-bisection

[apiraino]

Bisection probably leads to #111571 cc @jhpratt

TIL to look at the perf builds results, they help getting more context. They told me tha PR 111571 is actually commit 7e4f5ecde93e629a44ad3678059c5cd364791d27

[jhpratt]

I'll take a look at this after RustConf.

[jhpratt]

@apiraino Is it possible the bisection contained an error? I'm not seeing any possible connection. The errors seem unrelated, .unwrap() is not used anywhere in my PR, and proc_macro is not even present in any of the three linked logs.

[apiraino]

Ok, I give up on reproducing using the crate ellidri (in the latest nightlies the error changed, I can't track the original error anymore). So I've started again using the crate edu-sync I now have a stable reproducible.

I am now a bit more confident the regression is in 34ccd04 (specifically #114022) cc @oli-obk (I see in that patch some code that is in the stacktraces).

sorry @jhpratt for the ping and thanks for pointing me into the right direction :)

[jhpratt]

No worries! Someone mentioned that it may have been incorrect at RustConf, but I wanted to have a chance to look into it myself before saying anything.

I'll be unsubscribing from this issue; please ping if something needs my attention :)

[oli-obk]

small, but not yet minimal repro. Should be good enough for the test suite. I'm looking into a fix now.

use std::future::Future;

async fn bop() {
    fold(run(), |mut foo| async move {
        &mut foo.bar;
    })
}

fn fold<Fut, F, U>(_: Foo<U>, f: F)
where
    F: FnMut(Foo<U>) -> Fut,
{
    loop {}
}

struct Foo<F> {
    bar: Vec<F>,
}

fn run() -> Foo<impl Future<Output = ()>> {
    loop {}
}

[oli-obk]

I reverted all changes from #114022 and it does not appear to change behaviour. trying a local bisect on the minimal repro.

edit: hmm weird, it also points to that PR. Trying again
edit2: ok now it works, weird