rust-lang / rust-lang/rust

[ICE]: reborrow: size mismatch: compiler/rustc_const_eval/src/interpret/place.rs

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C-bug F-const_block_items F-reborrow I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

Code
#![feature(const_block_items)]
#![feature(reborrow)]
use std::marker::CoerceShared;
struct MyMut<'a>(&'a u8);
struct MyRef<'a> {
    x: &'a (),
    y: &'a (),
}

impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
const {
    let value = 1;
    foo(MyMut(&value));
}
const fn foo(x: MyRef) {}

fn main() {}
Meta

rustc --version --verbose:

rustc 1.98.0-nightly (bc2112ed5 2026-06-18)
binary: rustc
commit-hash: bc2112ed56c99fa649e09ab3ab286afab3d9059a
commit-date: 2026-06-18
host: x86_64-unknown-linux-gnu
release: 1.98.0-nightly
LLVM version: 22.1.7
Error output
error: implementing `CoerceShared` does not allow multiple lifetimes or fields to be coerced
  --> a.rs:10:10
   |
10 | impl<'a> CoerceShared<MyRef<'a>> for MyMut<'a> {}
   |          ^^^^^^^^^^^^^^^^^^^^^^^
Backtrace 

thread 'rustc' (1255357) panicked at /rustc-dev/bc2112ed56c99fa649e09ab3ab286afab3d9059a/compiler/rustc_const_eval/src/interpret/place.rs:936:17:
assertion `left == right` failed
  left: Size(8 bytes)
 right: Size(16 bytes)
stack backtrace:
   0:     0x7f38d19fd889 - <<std[9155b05baf46f0b5]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[b26e7c5dab710dcd]::fmt::Display>::fmt
   1:     0x7f38d200ebde - core[b26e7c5dab710dcd]::fmt::write
   2:     0x7f38d1a13cb6 - <std[9155b05baf46f0b5]::sys::stdio::unix::Stderr as std[9155b05baf46f0b5]::io::Write>::write_fmt
   3:     0x7f38d19d2b7e - std[9155b05baf46f0b5]::panicking::default_hook::{closure#0}
   4:     0x7f38d19f0573 - std[9155b05baf46f0b5]::panicking::default_hook
   5:     0x7f38d0a49fc1 - std[9155b05baf46f0b5]::panicking::update_hook::<alloc[4a86d35f348a3b04]::boxed::Box<rustc_driver_impl[b791fc15675dcea2]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f38d19f0852 - std[9155b05baf46f0b5]::panicking::panic_with_hook
   7:     0x7f38d19d2c42 - std[9155b05baf46f0b5]::panicking::panic_handler::{closure#0}
   8:     0x7f38d19c7169 - std[9155b05baf46f0b5]::sys::backtrace::__rust_end_short_backtrace::<std[9155b05baf46f0b5]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f38d19d46ad - __rustc[b4c4dac14d05b73]::rust_begin_unwind
  10:     0x7f38ce90455c - core[b26e7c5dab710dcd]::panicking::panic_fmt
  11:     0x7f38d040bbd3 - core[b26e7c5dab710dcd]::panicking::assert_failed_inner
  12:     0x7f38d0faf839 - core[b26e7c5dab710dcd]::panicking::assert_failed::<rustc_abi[c68f683fea65e658]::Size, rustc_abi[c68f683fea65e658]::Size>
  13:     0x7f38d2704b02 - <rustc_const_eval[a05529753b3711cc]::interpret::eval_context::InterpCx<rustc_const_eval[a05529753b3711cc]::const_eval::machine::CompileTimeMachine>>::copy_op_no_validate::<rustc_const_eval[a05529753b3711cc]::interpret::operand::OpTy, rustc_const_eval[a05529753b3711cc]::interpret::place::PlaceTy>
  14:     0x7f38d3040cc2 - <rustc_const_eval[a05529753b3711cc]::interpret::eval_context::InterpCx<rustc_const_eval[a05529753b3711cc]::const_eval::machine::CompileTimeMachine>>::eval_rvalue_into_place
  15:     0x7f38d300360d - rustc_const_eval[a05529753b3711cc]::const_eval::eval_queries::eval_to_allocation_raw_provider
  16:     0x7f38d3001c56 - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_allocation_raw::invoke_provider_fn::__rust_begin_short_backtrace
  17:     0x7f38d26d3970 - rustc_query_impl[f814d044a8094e2a]::execution::try_execute_query::<rustc_middle[cb7c4bb37f51aac1]::query::caches::DefaultCache<rustc_middle[cb7c4bb37f51aac1]::ty::PseudoCanonicalInput<rustc_middle[cb7c4bb37f51aac1]::mir::interpret::GlobalId>, rustc_middle[cb7c4bb37f51aac1]::query::erase::ErasedData<[u8; 24usize]>>, false>
  18:     0x7f38d26d3297 - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_allocation_raw::execute_query_non_incr::__rust_end_short_backtrace
  19:     0x7f38d26d18ca - rustc_const_eval[a05529753b3711cc]::const_eval::eval_queries::eval_to_const_value_raw_provider
  20:     0x7f38d26d151e - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_const_value_raw::invoke_provider_fn::__rust_begin_short_backtrace
  21:     0x7f38d26d37ac - rustc_query_impl[f814d044a8094e2a]::execution::try_execute_query::<rustc_middle[cb7c4bb37f51aac1]::query::caches::DefaultCache<rustc_middle[cb7c4bb37f51aac1]::ty::PseudoCanonicalInput<rustc_middle[cb7c4bb37f51aac1]::mir::interpret::GlobalId>, rustc_middle[cb7c4bb37f51aac1]::query::erase::ErasedData<[u8; 24usize]>>, false>
  22:     0x7f38d26d334f - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_const_value_raw::execute_query_non_incr::__rust_end_short_backtrace
  23:     0x7f38d26d23c5 - rustc_const_eval[a05529753b3711cc]::const_eval::eval_queries::eval_to_const_value_raw_provider
  24:     0x7f38d26d151e - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_const_value_raw::invoke_provider_fn::__rust_begin_short_backtrace
  25:     0x7f38d26d37ac - rustc_query_impl[f814d044a8094e2a]::execution::try_execute_query::<rustc_middle[cb7c4bb37f51aac1]::query::caches::DefaultCache<rustc_middle[cb7c4bb37f51aac1]::ty::PseudoCanonicalInput<rustc_middle[cb7c4bb37f51aac1]::mir::interpret::GlobalId>, rustc_middle[cb7c4bb37f51aac1]::query::erase::ErasedData<[u8; 24usize]>>, false>
  26:     0x7f38d26d334f - rustc_query_impl[f814d044a8094e2a]::query_impl::eval_to_const_value_raw::execute_query_non_incr::__rust_end_short_backtrace
  27:     0x7f38d24a842a - <rustc_middle[cb7c4bb37f51aac1]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_hir_analysis[f8649c0bc5b32aaa]::check_crate::{closure#1}>::{closure#0}
  28:     0x7f38d24a7a25 - rustc_hir_analysis[f8649c0bc5b32aaa]::check_crate
  29:     0x7f38d24a9d0c - rustc_interface[84e7048b04034882]::passes::analysis
  30:     0x7f38d317f906 - rustc_query_impl[f814d044a8094e2a]::execution::try_execute_query::<rustc_middle[cb7c4bb37f51aac1]::query::caches::SingleCache<rustc_middle[cb7c4bb37f51aac1]::query::erase::ErasedData<[u8; 0usize]>>, false>
  31:     0x7f38d317f5e9 - rustc_query_impl[f814d044a8094e2a]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  32:     0x7f38d3199c52 - rustc_interface[84e7048b04034882]::interface::run_compiler::<(), rustc_driver_impl[b791fc15675dcea2]::run_compiler::{closure#0}>::{closure#1}
  33:     0x7f38d31ceffa - std[9155b05baf46f0b5]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[84e7048b04034882]::util::run_in_thread_with_globals<rustc_interface[84e7048b04034882]::util::run_in_thread_pool_with_globals<rustc_interface[84e7048b04034882]::interface::run_compiler<(), rustc_driver_impl[b791fc15675dcea2]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  34:     0x7f38d31cedad - <std[9155b05baf46f0b5]::thread::lifecycle::spawn_unchecked<rustc_interface[84e7048b04034882]::util::run_in_thread_with_globals<rustc_interface[84e7048b04034882]::util::run_in_thread_pool_with_globals<rustc_interface[84e7048b04034882]::interface::run_compiler<(), rustc_driver_impl[b791fc15675dcea2]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[b26e7c5dab710dcd]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  35:     0x7f38d31c5290 - <std[9155b05baf46f0b5]::sys::thread::unix::Thread>::new::thread_start
  36:     0x7f38ccc981b9 - <unknown>
  37:     0x7f38ccd1d21c - <unknown>
  38:                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: please attach the file at `/tmp/IM/rustc-ice-2026-06-19T19_06_42-1255347.txt` to your bug report

note: rustc 1.98.0-nightly (bc2112ed5 2026-06-18) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [eval_to_allocation_raw] const-evaluating + checking `_`
#1 [eval_to_const_value_raw] simplifying constant for the type system `_`
#2 [eval_to_const_value_raw] simplifying constant for the type system `_`
#3 [analysis] running analysis passes on crate `a`
end of query stack
error: aborting due to 1 previous error

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the ICE with the minimal Rust example, then inspect compiler/rustc_const_eval/src/interpret/place.rs around line 936 and the copy_op_no_validate path shown in the backtrace. Trace the const-evaluation size mismatch for the reborrow case; done means the example reports a normal compiler diagnostic or compiles without an internal panic, with regression coverage for the case.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
compilers
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
45/100

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