Erroneous 'ref mut' in let-else binding causes ICE

[meithecatte]

Code

#![feature(let_else)]
fn main() {
    let Some(ref mut meow) = Some(()) else { return };
}

Meta

rustc --version --verbose:

rustc 1.57.0-nightly (c1026539b 2021-10-15)
binary: rustc
commit-hash: c1026539bd22e9d070988deaa47b1360cbc76436
commit-date: 2021-10-15
host: x86_64-unknown-linux-gnu
release: 1.57.0-nightly
LLVM version: 13.0.0

Error output

warning: unused variable: `meow`
 --> x.rs:3:22
  |
3 |     let Some(ref mut meow) = Some(()) else { return };
  |                      ^^^^ help: if this is intentional, prefix it with an underscore: `_meow`
  |
  = note: `#[warn(unused_variables)]` on by default

Backtrace

thread 'rustc' panicked at 'called `Option::unwrap()` on a `None` value', compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs:53:62
stack backtrace:
   0: rust_begin_unwind
             at /rustc/c1026539bd22e9d070988deaa47b1360cbc76436/library/std/src/panicking.rs:517:5
   1: core::panicking::panic_fmt
             at /rustc/c1026539bd22e9d070988deaa47b1360cbc76436/library/core/src/panicking.rs:100:14
   2: core::panicking::panic
             at /rustc/c1026539bd22e9d070988deaa47b1360cbc76436/library/core/src/panicking.rs:50:5
   3: rustc_borrowck::diagnostics::mutability_errors::<impl rustc_borrowck::MirBorrowckCtxt>::report_mutability_error
   4: rustc_borrowck::MirBorrowckCtxt::access_place
   5: <rustc_borrowck::MirBorrowckCtxt as rustc_mir_dataflow::framework::visitor::ResultsVisitor>::visit_statement_before_primary_effect
   6: <rustc_mir_dataflow::framework::direction::Forward as rustc_mir_dataflow::framework::direction::Direction>::visit_results_in_block
   7: rustc_borrowck::do_mir_borrowck
   8: rustc_infer::infer::InferCtxtBuilder::enter
   9: core::ops::function::FnOnce::call_once
  10: rustc_query_system::query::plumbing::try_execute_query
  11: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::mir_borrowck
  12: rustc_data_structures::sync::par_for_each_in
  13: rustc_session::utils::<impl rustc_session::session::Session>::time
  14: rustc_interface::passes::analysis
  15: rustc_query_system::query::plumbing::try_execute_query
  16: <rustc_query_impl::Queries as rustc_middle::ty::query::QueryEngine>::analysis
  17: rustc_interface::passes::QueryContext::enter
  18: rustc_interface::queries::<impl rustc_interface::interface::Compiler>::enter
  19: rustc_span::with_source_map
  20: scoped_tls::ScopedKey<T>::set