no errors encountered even though delay_span_bug issued', compiler/rustc_errors/src/lib.rs:1023:13

[pacak]

Code

#![allow(incomplete_features)]                                                                                                                                                                                                                
#![feature(const_generics)]
#![feature(const_evaluatable_checked)]

struct F<const S: &'static str>;
impl<const S: &'static str> X for F<{ S }> {
    const W: usize = 3;

    fn d(r: &[u8; Self::W]) -> F<{ S }> {
        let x: [u8; Self::W] = [0; Self::W];
        F
    }
}

pub trait X {
    const W: usize;
    fn d(r: &[u8; Self::W]) -> Self;
}

Meta

rustc --version --verbose:

rustc 1.55.0-nightly (406d4a9cc 2021-06-21)                                                                                                                                                                                                   
binary: rustc
commit-hash: 406d4a9cc3b9601cf98a07c6c83e0227d64f5d48
commit-date: 2021-06-21
host: x86_64-unknown-linux-gnu
release: 1.55.0-nightly
LLVM version: 12.0.1

Error output

error: internal compiler error: broken MIR in DefId(0:10 ~ lol[3197]::{impl#0}::d) (NoSolution): could not prove Binder(WellFormed([u8; _]), [])
  |
  = note: delayed at compiler/rustc_mir/src/borrow_check/type_check/mod.rs:253:27

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler/rustc_errors/src/lib.rs:1023:13

Backtrace

stack backtrace:
   0: rust_begin_unwind
             at /rustc/406d4a9cc3b9601cf98a07c6c83e0227d64f5d48/library/std/src/panicking.rs:515:5
   1: std::panicking::begin_panic_fmt
             at /rustc/406d4a9cc3b9601cf98a07c6c83e0227d64f5d48/library/std/src/panicking.rs:457:5
   2: rustc_errors::HandlerInner::flush_delayed
   3: <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop
   4: core::ptr::drop_in_place<rustc_session::parse::ParseSess>
   5: <alloc::rc::Rc<T> as core::ops::drop::Drop>::drop
   6: core::ptr::drop_in_place<rustc_interface::interface::Compiler>
   7: rustc_span::with_source_map
   8: rustc_interface::interface::create_compiler_and_run
   9: scoped_tls::ScopedKey<T>::set

[BoxyUwU]

More minimal repro:

#![feature(const_generics, const_evaluatable_checked)]
#![allow(incomplete_features)]                                                                                                                                                                                                                

pub trait Foo {
    const ASSOC_C: usize;
    fn foo() where [(); Self::ASSOC_C]:;
}

struct Bar<const N: &'static ()>;
impl<const N: &'static ()> Foo for Bar<N> {
    const ASSOC_C: usize = 3;

    fn foo() where [u8; Self::ASSOC_C]: {
        let _: [u8; Self::ASSOC_C] = loop {};
    }
}

[jackh726]

Fixed by #85499, marking as needs-test