[ICE]: `hir-typeck passed but Reborrow does not have a lifetime argument`

[matthiaskrgr]

auto-reduced (treereduce-rust):

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

struct CustomMarker<'a>(PhantomData<&'a ()>);
impl<'a> Reborrow for PhantomData<'a> {}

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

original:

//@ run-pass

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

struct CustomMarker<'a>(PhantomData<&'a ()>);
impl<'a> Reborrow for PhantomData<'a> {}

impl<'a> std::ops::Deref for CustomMarker<'a> {
    type Target = CustomMarker<'a>;
    fn deref(&self) -> &Self::Target {
        self
    }
}

impl<'a> std::ops::DerefMut for CustomMarker<'a> {
    fn deref_mut(&mut self) -> &mut Self::Target {
        self
    }
}

fn main() {
    let mut a = CustomMarker(PhantomData);

    *a = CustomMarker(PhantomData);
}

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/borrow_set.rs

Lines 307 to 319 in 3e353d7

	let &ty::Adt(reborrowed_adt, _reborrowed_args) = borrowed_place_ty.kind() else {
	unreachable!()
	};
	let &ty::Adt(target_adt, assigned_args) = target.kind() else { unreachable!() };
	let Some(ty::GenericArgKind::Lifetime(region)) = assigned_args.get(0).map(|r| r.kind())
	else {
	bug!(
	"hir-typeck passed but {} does not have a lifetime argument",
	if mutability == Mutability::Mut { "Reborrow" } else { "CoerceShared" }
	);
	};
	let region = region.as_var();
	let kind = if mutability == Mutability::Mut {

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc

Program output

error[E0107]: struct takes 0 lifetime arguments but 1 lifetime argument was supplied
   --> /tmp/icemaker_global_tempdir.HFhzK8XG8tRD/rustc_testrunner_tmpdir_reporting.ZH8KibTRlyKp/mvce.rs:5:23
    |
  5 | impl<'a> Reborrow for PhantomData<'a> {}
    |                       ^^^^^^^^^^^---- help: remove the unnecessary generics
    |                       |
    |                       expected 0 lifetime arguments
    |
note: struct defined here, with 0 lifetime parameters
   --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/marker.rs:811:12
    |
811 | pub struct PhantomData<T: PointeeSized>;
    |            ^^^^^^^^^^^

error[E0107]: struct takes 1 generic argument but 0 generic arguments were supplied
   --> /tmp/icemaker_global_tempdir.HFhzK8XG8tRD/rustc_testrunner_tmpdir_reporting.ZH8KibTRlyKp/mvce.rs:5:23
    |
  5 | impl<'a> Reborrow for PhantomData<'a> {}
    |                       ^^^^^^^^^^^ expected 1 generic argument
    |
note: struct defined here, with 1 generic parameter: `T`
   --> /home/matthias/.rustup/toolchains/master/lib/rustlib/src/rust/library/core/src/marker.rs:811:12
    |
811 | pub struct PhantomData<T: PointeeSized>;
    |            ^^^^^^^^^^^ -
help: add missing generic argument
    |
  5 | impl<'a> Reborrow for PhantomData<'a, T> {}
    |                                     +++

error: implementing `Reborrow` does not allow multiple lifetimes or fields to be coerced
 --> /tmp/icemaker_global_tempdir.HFhzK8XG8tRD/rustc_testrunner_tmpdir_reporting.ZH8KibTRlyKp/mvce.rs:5:1
  |
5 | impl<'a> Reborrow for PhantomData<'a> {}
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: internal compiler error: /rustc-dev/3e353d7353b0cd6fa4eefd5c882457cc2708184c/compiler/rustc_borrowck/src/borrow_set.rs:313:17: hir-typeck passed but Reborrow does not have a lifetime argument


thread 'rustc' (4044579) panicked at /rustc-dev/3e353d7353b0cd6fa4eefd5c882457cc2708184c/compiler/rustc_borrowck/src/borrow_set.rs:313:17:
Box<dyn Any>
stack backtrace:
   0:     0x7fba3d874239 - <<std[db65628f2330fd11]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[b3c617e8375f9bd0]::fmt::Display>::fmt
   1:     0x7fba3de1b788 - core[b3c617e8375f9bd0]::fmt::write
   2:     0x7fba3d88ac66 - <std[db65628f2330fd11]::sys::stdio::unix::Stderr as std[db65628f2330fd11]::io::Write>::write_fmt
   3:     0x7fba3d84a2de - std[db65628f2330fd11]::panicking::default_hook::{closure#0}
   4:     0x7fba3d8678f3 - std[db65628f2330fd11]::panicking::default_hook
   5:     0x7fba3c7544d1 - std[db65628f2330fd11]::panicking::update_hook::<alloc[b10a1c065189447]::boxed::Box<rustc_driver_impl[1f444ccaa450aabc]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7fba3d867bd2 - std[db65628f2330fd11]::panicking::panic_with_hook
   7:     0x7fba3c781f51 - std[db65628f2330fd11]::panicking::begin_panic::<rustc_errors[4e25407aa9dfcb98]::ExplicitBug>::{closure#0}
   8:     0x7fba3c77af46 - std[db65628f2330fd11]::sys::backtrace::__rust_end_short_backtrace::<std[db65628f2330fd11]::panicking::begin_panic<rustc_errors[4e25407aa9dfcb98]::ExplicitBug>::{closure#0}, !>
   9:     0x7fba3c77acab - std[db65628f2330fd11]::panicking::begin_panic::<rustc_errors[4e25407aa9dfcb98]::ExplicitBug>
  10:     0x7fba3c78d431 - <rustc_errors[4e25407aa9dfcb98]::diagnostic::BugAbort as rustc_errors[4e25407aa9dfcb98]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
  11:     0x7fba3cd9cf69 - rustc_middle[4a2cff3451d2bad5]::util::bug::opt_span_bug_fmt::<rustc_span[749aae40fdac821d]::span_encoding::Span>::{closure#0}
  12:     0x7fba3cd9d0d2 - rustc_middle[4a2cff3451d2bad5]::ty::context::tls::with_opt::<rustc_middle[4a2cff3451d2bad5]::util::bug::opt_span_bug_fmt<rustc_span[749aae40fdac821d]::span_encoding::Span>::{closure#0}, !>::{closure#0}
  13:     0x7fba3cd8b82b - rustc_middle[4a2cff3451d2bad5]::ty::context::tls::with_context_opt::<rustc_middle[4a2cff3451d2bad5]::ty::context::tls::with_opt<rustc_middle[4a2cff3451d2bad5]::util::bug::opt_span_bug_fmt<rustc_span[749aae40fdac821d]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
  14:     0x7fba3a731134 - rustc_middle[4a2cff3451d2bad5]::util::bug::bug_fmt
  15:     0x7fba3b287486 - <rustc_borrowck[543291a75b63dc2a]::borrow_set::BorrowSet>::build
  16:     0x7fba3e8d6e5b - <rustc_borrowck[543291a75b63dc2a]::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
  17:     0x7fba3e8d2b1b - rustc_borrowck[543291a75b63dc2a]::mir_borrowck
  18:     0x7fba3e8d28e9 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::mir_borrowck::invoke_provider_fn::__rust_begin_short_backtrace
  19:     0x7fba3df6d6a6 - 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>
  20:     0x7fba3df6fdc3 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::mir_borrowck::execute_query_non_incr::__rust_end_short_backtrace
  21:     0x7fba3df6ff94 - <rustc_middle[4a2cff3451d2bad5]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[232b63f46aa35c0e]::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  22:     0x7fba3df6f276 - rustc_interface[232b63f46aa35c0e]::passes::analysis
  23:     0x7fba3ef822c9 - rustc_query_impl[3b9ecabc2cca1a8f]::execution::try_execute_query::<rustc_middle[4a2cff3451d2bad5]::query::caches::SingleCache<rustc_middle[4a2cff3451d2bad5]::query::erase::ErasedData<[u8; 0usize]>>, false>
  24:     0x7fba3ef81f33 - rustc_query_impl[3b9ecabc2cca1a8f]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  25:     0x7fba3efc765b - rustc_interface[232b63f46aa35c0e]::interface::run_compiler::<(), rustc_driver_impl[1f444ccaa450aabc]::run_compiler::{closure#0}>::{closure#1}
  26:     0x7fba3ef75c3e - 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}, ()>
  27:     0x7fba3ef7632d - <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}
  28:     0x7fba3ef7712c - <std[db65628f2330fd11]::sys::thread::unix::Thread>::new::thread_start
  29:     0x7fba38aa597a - <unknown>
  30:     0x7fba38b292bc - <unknown>
  31:                0x0 - <unknown>

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

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 4 previous errors

For more information about this error, try `rustc --explain E0107`.

@rustbot label +F-reborrow

[matthiaskrgr]

smaller

#![feature(reborrow)]
use std::marker::{PhantomData, Reborrow};
struct CustomMarker<'a>(PhantomData<&'a ()>);
impl<T> Reborrow for PhantomData<T> {}
fn main() {
    CustomMarker(PhantomData);
}

[theemathas]

Related to #156307. cc @aapoalas

[matthiaskrgr]

ah lol 😆

[matthiaskrgr]

to hit the CoerceShared branch:

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