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False E0644 closure/generator type that references itself; new in nightly-2022-11-05 #104025

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kpreid opened this issue Nov 5, 2022 · 1 comment · Fixed by #104038
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A-closures Area: closures (`|args| { .. }`) C-bug Category: This is a bug. regression-from-stable-to-nightly Performance or correctness regression from stable to nightly.

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@kpreid
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kpreid commented Nov 5, 2022

I tried this code with cargo +nightly-2022-11-05 check:

pub trait Fn0: Fn() -> Self::Out {
    type Out;
}

impl<F: Fn() -> ()> Fn0 for F {
    type Out = ();
}

pub fn closure_typer(_: impl Fn0) {}

fn main() {
    closure_typer(move || {});
}

I expected to see this happen: successful compilation

Instead, this happened:

error[E0644]: closure/generator type that references itself
  --> src/bin/cyclic-repro.rs:13:19
   |
13 |     closure_typer(move || {});
   |                   ^^^^^^^^^^ cyclic type of infinite size
   |
   = note: closures cannot capture themselves or take themselves as argument;
           this error may be the result of a recent compiler bug-fix,
           see issue #46062 <https://github.com/rust-lang/rust/issues/46062>
           for more information

It compiles successfully with the preceding nightly, cargo +nightly-2022-11-04 check, and stable 1.65.0.

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rustc --version --verbose:

rustc 1.67.0-nightly (09508489e 2022-11-04)
binary: rustc
commit-hash: 09508489efc223287731fe8abbd2a81bbf7adf8e
commit-date: 2022-11-04
host: x86_64-apple-darwin
release: 1.67.0-nightly
LLVM version: 15.0.4

To be clear, this is the nightly I installed with rustup install nightly-2022-11-05. I assume it's normal for the commit date to be a day earlier, but I haven't specifically noticed that before.

Related

This sounds extremely similar to #97680, but that bug was reported months earlier whereas this one appeared today. My original discovery involved async fn traits too, but I reduced it to an example which contains only a closure.

@rustbot label regression-from-stable-to-nightly A-closures

@kpreid kpreid added the C-bug Category: This is a bug. label Nov 5, 2022
@rustbot rustbot added A-closures Area: closures (`|args| { .. }`) regression-from-stable-to-nightly Performance or correctness regression from stable to nightly. I-prioritize Issue: Indicates that prioritization has been requested for this issue. labels Nov 5, 2022
@compiler-errors
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This was introduced by me in #101834 -- I'll put up a fix soon.

@compiler-errors compiler-errors self-assigned this Nov 6, 2022
@bors bors closed this as completed in f0bd2cd Nov 7, 2022
@apiraino apiraino removed the I-prioritize Issue: Indicates that prioritization has been requested for this issue. label Nov 9, 2022
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Labels
A-closures Area: closures (`|args| { .. }`) C-bug Category: This is a bug. regression-from-stable-to-nightly Performance or correctness regression from stable to nightly.
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4 participants