ICE: `where` clause with const evaluation on `fn` crashes, but on `impl` gives normal error

[Kiiyya]

One version crashes the compiler, the other version produces a normal error.
Note that commenting out the line in main() makes it compile just fine.

Code

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

use std::sync::Arc;

pub enum Predicate<const EXPRESSION: bool> {}
pub trait Satisfied {}
impl Satisfied for Predicate<true> {}

pub trait Depth { const DEPTH: usize; }

/// Make it impossible to have cyclic Arc references.
pub struct AcArc<T: Depth, const D: usize> {
    #[allow(dead_code)]
    inner: Arc<T>,
}

impl<T: Depth, const D: usize> AcArc<T, D> {
    pub fn new(item: T) -> Self
        where Predicate<{T::DEPTH <= D}>: Satisfied, // crashes with == too.
    {
        Self {
            inner: Arc::new(item),
        }
    }
}

// With the predicate on the impl instead of on the function, it gives a "normal" error.
// Though I still feel like main() should typecheck.
// impl<T: Depth, const D: usize> AcArc<T, D>
//     where Predicate<{T::DEPTH == D}>: Satisfied,
// {
//     pub fn new(item: T) -> Self
//     {
//         Self {
//             inner: Arc::new(item),
//         }
//     }
// }

// this is where the depth increment is enforced.
// But compiler crashes without this.
// impl<T, const D: usize> Depth for AcArc<T, D>
// where
//     T: Depth,
// {
//     const DEPTH: usize = D + 1;
// }

impl Depth for u8 { const DEPTH: usize = 0; }

fn main() {
    let arc : AcArc<u8, 0> = AcArc::new(42_u8); // comment this out and it compiles just fine.

    println!("Hello, world!");
}

Meta

rustc --version --verbose:

rustc 1.52.0-nightly (caca2121f 2021-03-05)
binary: rustc
commit-hash: caca2121ffe4cb47d8ea2d9469c493995f57e0b5
commit-date: 2021-03-05
host: x86_64-pc-windows-msvc
release: 1.52.0-nightly
LLVM version: 12.0.0

Error output

PS E:\hax\rust-crashie> cargo b
   Compiling rust-crashie v0.1.0 (E:\hax\rust-crashie)

(((some irrelevant warning ommitted)))

warning: Error finalizing incremental compilation session directory `\\?\E:\hax\rust-crashie\target\debug\incremental\rust_crashie-2f5q55yas46ec\s-fwhefzjcfw-15fjgh-working`: The system cannot find the file specified. (os error 2)

warning: 4 warnings emitted

error: internal compiler error: Encountered error `Unimplemented` selecting `Binder(<^0 as Depth>)` during codegen
  |
  = note: delayed at compiler\rustc_trait_selection\src\traits\codegen.rs:68:32

error: internal compiler error: ty::ConstKind::Error constructed but no error reported.
  |
  = note: delayed at /rustc/caca2121ffe4cb47d8ea2d9469c493995f57e0b5\compiler\rustc_middle\src\ty\consts.rs:182:43

error: internal compiler error: `ErrorReported` without an error
  --> src\main.rs:53:30
   |
53 |     let arc : AcArc<u8, 0> = AcArc::new(42_u8);
   |                              ^^^^^^^^^^
   |
   = note: delayed at compiler\rustc_trait_selection\src\traits\error_reporting\mod.rs:747:31

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler\rustc_errors\src\lib.rs:1012:13
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

error: internal compiler error: unexpected panic

note: the compiler unexpectedly panicked. this is a bug.

note: we would appreciate a bug report: https://github.com/rust-lang/rust/issues/new?labels=C-bug%2C+I-ICE%2C+T-compiler&template=ice.md

note: rustc 1.52.0-nightly (caca2121f 2021-03-05) running on x86_64-pc-windows-msvc

note: compiler flags: -C embed-bitcode=no -C debuginfo=2 -C incremental --crate-type bin

note: some of the compiler flags provided by cargo are hidden

query stack during panic:
end of query stack
error: could not compile `rust-crashie`

To learn more, run the command again with --verbose.

Error with where on impl instead

Though I still feel like this should typecheck, at least in the future some day?

error[E0599]: the function or associated item `new` exists for struct `AcArc<_, {_: usize}>`, but its trait bounds were not satisfied
  --> src\main.rs:53:37
   |
6  | pub enum Predicate<const EXPRESSION: bool> {}
   | ------------------------------------------ doesn't satisfy `Predicate<{T::DEPTH == D}>: Satisfied`
...
13 | pub struct AcArc<T: Depth, const D: usize> {
   | ------------------------------------------ function or associated item `new` not found for this
...
53 |     let arc : AcArc<u8, 0> = AcArc::new(42_u8);
   |                                     ^^^ function or associated item cannot be called on `AcArc<_, {_: usize}>` due to unsatisfied trait bounds
   |
   = note: the following trait bounds were not satisfied:
           `Predicate<{T::DEPTH == D}>: Satisfied`

Backtrace (`FULL`)

thread 'rustc' panicked at 'no errors encountered even though `delay_span_bug` issued', compiler\rustc_errors\src\lib.rs:1012:13
stack backtrace:
   0:     0x7ffadc18879e - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h804aacc93092d135
   1:     0x7ffadc1b404c - core::fmt::write::h2daf2a210ae0d5f0
   2:     0x7ffadc17c158 - <std::io::IoSlice as core::fmt::Debug>::fmt::hfa239d9348f09840
   3:     0x7ffadc18c93d - std::panicking::take_hook::h930d1e1d0a893a3f
   4:     0x7ffadc18c409 - std::panicking::take_hook::h930d1e1d0a893a3f
   5:     0x7ffadc6b23d5 - rustc_driver::report_ice::h5f2d10e8face884a
   6:     0x7ffadc18d1a5 - std::panicking::rust_panic_with_hook::h291b58940b8c1567
   7:     0x7ffadc18cd01 - rust_begin_unwind
   8:     0x7ffadc1890ef - <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt::h804aacc93092d135
   9:     0x7ffadc18cc59 - rust_begin_unwind
  10:     0x7ffadc1e583c - std::panicking::begin_panic_fmt::h21676d8d2c928240
  11:     0x7ffae0914c24 - rustc_errors::HandlerInner::delay_as_bug::h84ea15161c493c2b
  12:     0x7ffae09101d7 - <rustc_errors::HandlerInner as core::ops::drop::Drop>::drop::h2aadc8469749ba5c
  13:     0x7ffadc6bda87 - rustc_errors::snippet::MultilineAnnotation::increase_depth::h0d6a408d57c96b60
  14:     0x7ffadc6c46ba - rustc_errors::snippet::MultilineAnnotation::increase_depth::h0d6a408d57c96b60
  15:     0x7ffadc6bf46c - rustc_errors::snippet::MultilineAnnotation::increase_depth::h0d6a408d57c96b60
  16:     0x7ffadc6b481d - <rustc_driver::Compilation as core::fmt::Debug>::fmt::h34129260871bdb31
  17:     0x7ffadc6cccc6 - <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt::h7de05d943e0a531e
  18:     0x7ffadc6c7d24 - rustc_errors::snippet::MultilineAnnotation::increase_depth::h0d6a408d57c96b60
  19:     0x7ffadc6cddbd - <rustc_middle::ty::SymbolName as core::fmt::Debug>::fmt::h7de05d943e0a531e
  20:     0x7ffadc6f101d - <tracing_subscriber::util::TryInitError as core::fmt::Display>::fmt::hc634bfbe27699956
  21:     0x7ffadc19c83a - std::sys::windows::thread::Thread::new::h13c38e7cd538470c
  22:     0x7ffb374c7034 - BaseThreadInitThunk
  23:     0x7ffb375fd241 - RtlUserThreadStart

[lcnr]

same underlying issue as #83249, closing in favor of that one