[ICE]: called `Result::unwrap()` on an `Err` value: NoSolution

[matthiaskrgr]

auto-reduced (treereduce-rust):

//@compile-flags: --edition=2024


#![feature(reborrow)]
use std::marker::{CoerceShared, PhantomData, Reborrow};

struct CustomMarker<'a>(PhantomData<&'a ()>);


struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
impl<'a> CoerceShared<CustomMarkerRef<'a>> for CustomMarker<'a> {}


fn method<'a>(_a: CustomMarkerRef<'a>) -> 'a () {
    &()
}

fn main() {
    let a = CustomMarker(PhantomData);
    let b = method(a);
    
    
}

original:

//@ run-pass

#![feature(reborrow)]
use std::marker::{CoerceShared, PhantomData, Reborrow};

struct CustomMarker<'a>(PhantomData<&'a ()>);
impl<'a> Reborrow for CustomMarker<'CoerceShared> {}
#[derive(Debug, Clone, Copy)]
struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
impl<'a> CoerceShared<CustomMarkerRef<'a>> for CustomMarker<'a> {}


fn method<'a>(_a: CustomMarkerRef<'a>) -> 'a () {
    &()
}

fn main() {
    let a = CustomMarker(PhantomData);
    let b = method(a);
    let c = method(a);
    let _ = (b, c);
}

Version information

rustc 1.97.0-nightly (3e353d735 2026-05-08)
binary: rustc
commit-hash: 3e353d7353b0cd6fa4eefd5c882457cc2708184c
commit-date: 2026-05-08
host: x86_64-unknown-linux-gnu
release: 1.97.0-nightly
LLVM version: 22.1.4

Possibly related line of code:

rust/compiler/rustc_borrowck/src/type_check/mod.rs

Lines 2523 to 2535 in 3e353d7

	borrowed_ty,
	ty::Variance::Covariant,
	dest_ty,
	location.to_locations(),
	category,
	)
	.unwrap();
	}
	}
	} else {
	// Exclusive reborrow
	self.relate_types(
	borrowed_ty,

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc --edition=2024

Program output

error: expected type, found lifetime
  --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:13:43
   |
13 | fn method<'a>(_a: CustomMarkerRef<'a>) -> 'a () {
   |                                           ^^ expected type
   |
help: you might have meant to write a reference type here
   |
13 | fn method<'a>(_a: CustomMarkerRef<'a>) -> &'a () {
   |                                           +

error[E0573]: expected type, found derive macro `Debug`
 --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:9:41
  |
9 | struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
  |                                         ^^^^^ not a type
  |
help: consider importing this trait instead
  |
4 + use std::fmt::Debug;
  |

warning: unused import: `Reborrow`
 --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:4:46
  |
4 | use std::marker::{CoerceShared, PhantomData, Reborrow};
  |                                              ^^^^^^^^
  |
  = note: `#[warn(unused_imports)]` (part of `#[warn(unused)]`) on by default

error[E0782]: expected a type, found a trait
 --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:9:48
  |
9 | struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
  |                                                ^^^^^
  |
help: you can add the `dyn` keyword if you want a trait object
  |
9 | struct CustomMarkerRef<'a>(PhantomData<(Debug, dyn Clone, Copy)>);
  |                                                +++

error[E0782]: expected a type, found a trait
 --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:9:55
  |
9 | struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
  |                                                       ^^^^
  |
help: you can add the `dyn` keyword if you want a trait object
  |
9 | struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, dyn Copy)>);
  |                                                       +++

error[E0277]: the trait bound `CustomMarkerRef<'a>: Copy` is not satisfied
    --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:10:10
     |
  10 | impl<'a> CoerceShared<CustomMarkerRef<'a>> for CustomMarker<'a> {}
     |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Copy` is not implemented for `CustomMarkerRef<'a>`
     |
note: required by a bound in `CoerceShared`
    --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/marker.rs:1363:32
     |
1363 | pub trait CoerceShared<Target: Copy>: Reborrow {
     |                                ^^^^ required by this bound in `CoerceShared`
help: consider annotating `CustomMarkerRef<'a>` with `#[derive(Copy)]`
     |
   9 + #[derive(Copy)]
  10 | struct CustomMarkerRef<'a>(PhantomData<(Debug, Clone, Copy)>);
     |

error[E0277]: the trait bound `CustomMarker<'a>: Reborrow` is not satisfied
    --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:10:48
     |
  10 | impl<'a> CoerceShared<CustomMarkerRef<'a>> for CustomMarker<'a> {}
     |                                                ^^^^^^^^^^^^^^^^ unsatisfied trait bound
     |
help: the nightly-only, unstable trait `Reborrow` is not implemented for `CustomMarker<'a>`
    --> /tmp/icemaker_global_tempdir.mCrvX9yCDWyy/rustc_testrunner_tmpdir_reporting.fUKak9Z01wCD/mvce.rs:6:1
     |
   6 | struct CustomMarker<'a>(PhantomData<&'a ()>);
     | ^^^^^^^^^^^^^^^^^^^^^^^
note: required by a bound in `CoerceShared`
    --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/marker.rs:1363:39
     |
1363 | pub trait CoerceShared<Target: Copy>: Reborrow {
     |                                       ^^^^^^^^ required by this bound in `CoerceShared`


thread 'rustc' (4098030) panicked at /rustc-dev/3e353d7353b0cd6fa4eefd5c882457cc2708184c/compiler/rustc_borrowck/src/type_check/mod.rs:2529:22:
called `Result::unwrap()` on an `Err` value: NoSolution
stack backtrace:
   0:     0x7fcc4f074239 - <<std[db65628f2330fd11]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[b3c617e8375f9bd0]::fmt::Display>::fmt
   1:     0x7fcc4f61b788 - core[b3c617e8375f9bd0]::fmt::write
   2:     0x7fcc4f08ac66 - <std[db65628f2330fd11]::sys::stdio::unix::Stderr as std[db65628f2330fd11]::io::Write>::write_fmt
   3:     0x7fcc4f04a2de - std[db65628f2330fd11]::panicking::default_hook::{closure#0}
   4:     0x7fcc4f0678f3 - std[db65628f2330fd11]::panicking::default_hook
   5:     0x7fcc4df544d1 - std[db65628f2330fd11]::panicking::update_hook::<alloc[b10a1c065189447]::boxed::Box<rustc_driver_impl[1f444ccaa450aabc]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fcc4f067bd2 - std[db65628f2330fd11]::panicking::panic_with_hook
   7:     0x7fcc4f04a3a2 - std[db65628f2330fd11]::panicking::panic_handler::{closure#0}
   8:     0x7fcc4f0410b9 - std[db65628f2330fd11]::sys::backtrace::__rust_end_short_backtrace::<std[db65628f2330fd11]::panicking::panic_handler::{closure#0}, !>
   9:     0x7fcc4f04be0d - __rustc[87b1f669d989e0ab]::rust_begin_unwind
  10:     0x7fcc4c12c50c - core[b3c617e8375f9bd0]::panicking::panic_fmt
  11:     0x7fcc4b799682 - core[b3c617e8375f9bd0]::result::unwrap_failed
  12:     0x7fcc504c23c7 - <rustc_borrowck[543291a75b63dc2a]::type_check::TypeChecker as rustc_middle[4a2cff3451d2bad5]::mir::visit::Visitor>::visit_body
  13:     0x7fcc5047286c - rustc_borrowck[543291a75b63dc2a]::type_check::type_check
  14:     0x7fcc500d7176 - <rustc_borrowck[543291a75b63dc2a]::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
  15:     0x7fcc500d2b1b - rustc_borrowck[543291a75b63dc2a]::mir_borrowck
  16:     0x7fcc500d28e9 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::mir_borrowck::invoke_provider_fn::__rust_begin_short_backtrace
  17:     0x7fcc4f76d6a6 - rustc_query_impl[3b9ecabc2cca1a8f]::execution::try_execute_query::<rustc_data_structures[4a3bb46d707d6722]::vec_cache::VecCache<rustc_span[749aae40fdac821d]::def_id::LocalDefId, rustc_middle[4a2cff3451d2bad5]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[4a2cff3451d2bad5]::dep_graph::graph::DepNodeIndex>, false>
  18:     0x7fcc4f76fdc3 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::mir_borrowck::execute_query_non_incr::__rust_end_short_backtrace
  19:     0x7fcc4f76ff94 - <rustc_middle[4a2cff3451d2bad5]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[232b63f46aa35c0e]::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  20:     0x7fcc4f76f276 - rustc_interface[232b63f46aa35c0e]::passes::analysis
  21:     0x7fcc507822c9 - rustc_query_impl[3b9ecabc2cca1a8f]::execution::try_execute_query::<rustc_middle[4a2cff3451d2bad5]::query::caches::SingleCache<rustc_middle[4a2cff3451d2bad5]::query::erase::ErasedData<[u8; 0usize]>>, false>
  22:     0x7fcc50781f33 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  23:     0x7fcc507c765b - rustc_interface[232b63f46aa35c0e]::interface::run_compiler::<(), rustc_driver_impl[1f444ccaa450aabc]::run_compiler::{closure#0}>::{closure#1}
  24:     0x7fcc50775c3e - std[db65628f2330fd11]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[232b63f46aa35c0e]::util::run_in_thread_with_globals<rustc_interface[232b63f46aa35c0e]::util::run_in_thread_pool_with_globals<rustc_interface[232b63f46aa35c0e]::interface::run_compiler<(), rustc_driver_impl[1f444ccaa450aabc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  25:     0x7fcc5077632d - <std[db65628f2330fd11]::thread::lifecycle::spawn_unchecked<rustc_interface[232b63f46aa35c0e]::util::run_in_thread_with_globals<rustc_interface[232b63f46aa35c0e]::util::run_in_thread_pool_with_globals<rustc_interface[232b63f46aa35c0e]::interface::run_compiler<(), rustc_driver_impl[1f444ccaa450aabc]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[b3c617e8375f9bd0]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  26:     0x7fcc5077712c - <std[db65628f2330fd11]::sys::thread::unix::Thread>::new::thread_start
  27:     0x7fcc4a2a597a - <unknown>
  28:     0x7fcc4a3292bc - <unknown>
  29:                0x0 - <unknown>

error: 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: please make sure that you have updated to the latest nightly

note: rustc 1.97.0-nightly (3e353d735 2026-05-08) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z dump-mir-dir=dir

query stack during panic:
#0 [mir_borrowck] borrow-checking `main`
#1 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 6 previous errors; 1 warning emitted

Some errors have detailed explanations: E0277, E0573, E0782.
For more information about an error, try `rustc --explain E0277`.

@rustbot label +F-reborrow

[matthiaskrgr]

//@compile-flags: --edition=2024
#![feature(reborrow)]
use std::marker::{CoerceShared, PhantomData};
struct CustomMarker<'a>(PhantomData<&'a ()>);
struct CustomMarkerRef;
impl<'a> CoerceShared<CustomMarkerRef> for CustomMarker<'a> {}
fn method(_a: CustomMarkerRef) {
    let a = CustomMarker(PhantomData);
    method(a)
}

fn main() {}