heapless 0.9.1 compiler panic in release mode

[simpsoneric]

Compiling heapless = "0.9.1" in release mode appears to cause a panic.

cargo init foo
cargo add heapless
cargo build --release

cargo build passes ok.

Code

$ cat Cargo.toml
[package]
name = "foo"
version = "0.1.0"
edition = "2024"

[dependencies]
heapless = "0.9.1"

Meta

rustc --version --verbose:

$ rustc --version --verbose
rustc 1.86.0 (05f9846f8 2025-03-31)
binary: rustc
commit-hash: 05f9846f893b09a1be1fc8560e33fc3c815cfecb
commit-date: 2025-03-31
host: x86_64-unknown-linux-gnu
release: 1.86.0
LLVM version: 19.1.7

Error output

<output>

Backtrace

$ RUST_BACKTRACE=1 cargo build --release
   Compiling heapless v0.9.1

thread 'rustc' panicked at compiler/rustc_errors/src/lib.rs:675:17:
`trimmed_def_paths` called, diagnostics were expected but none were emitted. Use `with_no_trimmed_paths` for debugging. This happened in the following `must_produce_diag` call's backtrace:
   0: <rustc_errors::DiagCtxtHandle>::set_must_produce_diag
   1: <rustc_session::session::Session>::record_trimmed_def_paths
   2: rustc_middle::ty::print::pretty::trimmed_def_paths
   3: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::trimmed_def_paths::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
   4: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::SingleCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
   5: rustc_query_impl::query_impl::trimmed_def_paths::get_query_non_incr::__rust_end_short_backtrace
   6: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::Printer>::print_def_path
   7: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::Printer>::print_def_path
   8: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_type
   9: <rustc_type_ir::ty_kind::TypeAndMut<rustc_middle::ty::context::TyCtxt> as rustc_middle::ty::print::Print<rustc_middle::ty::print::pretty::FmtPrinter>>::print
  10: <rustc_middle::ty::print::pretty::FmtPrinter as rustc_middle::ty::print::pretty::PrettyPrinter>::pretty_print_type
  11: <rustc_middle::ty::Ty as core::fmt::Display>::fmt
  12: core::fmt::write
  13: alloc::fmt::format::format_inner
  14: <rustc_mir_transform::validate::TypeChecker as rustc_middle::mir::visit::Visitor>::visit_rvalue
  15: rustc_mir_transform::validate::validate_types
  16: rustc_mir_transform::inline::process_blocks::<rustc_mir_transform::inline::NormalInliner>
  17: <rustc_mir_transform::inline::Inline as rustc_mir_transform::pass_manager::MirPass>::run_pass
  18: rustc_mir_transform::pass_manager::run_passes_inner
  19: rustc_mir_transform::optimized_mir
  20: rustc_query_impl::plumbing::__rust_begin_short_backtrace::<rustc_query_impl::query_impl::optimized_mir::dynamic_query::{closure#2}::{closure#0}, rustc_middle::query::erase::Erased<[u8; 8]>>
  21: rustc_query_system::query::plumbing::try_execute_query::<rustc_query_impl::DynamicConfig<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>, false, false, false>, rustc_query_impl::plumbing::QueryCtxt, false>
  22: rustc_query_impl::query_impl::optimized_mir::get_query_non_incr::__rust_end_short_backtrace
  23: rustc_middle::query::plumbing::query_get_at::<rustc_query_system::query::caches::DefIdCache<rustc_middle::query::erase::Erased<[u8; 8]>>>
  24: <rustc_metadata::rmeta::encoder::EncodeContext>::encode_crate_root
  25: rustc_metadata::rmeta::encoder::encode_metadata
  26: rustc_metadata::fs::encode_and_write_metadata
  27: <rustc_interface::queries::Linker>::codegen_and_build_linker
  28: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>::{closure#2}::{closure#0}
  29: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
  30: std::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  31: <<std::thread::Builder>::spawn_unchecked_<rustc_interface::util::run_in_thread_with_globals<rustc_interface::util::run_in_thread_pool_with_globals<rustc_interface::interface::run_compiler<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  32: std::sys::pal::unix::thread::Thread::new::thread_start
  33: start_thread
             at ./nptl/pthread_create.c:447:8
  34: clone3
             at ./misc/../sysdeps/unix/sysv/linux/x86_64/clone3.S:78:0

stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: <rustc_errors::DiagCtxtInner as core::ops::drop::Drop>::drop
   3: core::ptr::drop_in_place::<rustc_errors::DiagCtxt>
   4: core::ptr::drop_in_place::<rustc_session::parse::ParseSess>
   5: core::ptr::drop_in_place::<rustc_interface::interface::Compiler>
   6: rustc_interface::interface::run_compiler::<(), rustc_driver_impl::run_compiler::{closure#0}>::{closure#1}
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

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: rustc 1.86.0 (05f9846f8 2025-03-31) running on x86_64-unknown-linux-gnu

note: compiler flags: --crate-type lib -C opt-level=3 -C embed-bitcode=no -C strip=debuginfo

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

query stack during panic:
end of query stack
error: could not compile `heapless` (lib)

Caused by:
  process didn't exit successfully: `/home/er20605/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustc --crate-name heapless --edition=2021 /home/er20605/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/heapless-0.9.1/src/lib.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=150 --crate-type lib --emit=dep-info,metadata,link -C opt-level=3 -C embed-bitcode=no --check-cfg 'cfg(docsrs,test)' --check-cfg 'cfg(feature, values("alloc", "bytes", "defmt", "mpmc_large", "nightly", "portable-atomic", "portable-atomic-critical-section", "portable-atomic-unsafe-assume-single-core", "serde", "ufmt"))' -C metadata=94ed9d3818aa8e1a -C extra-filename=-e886d5429ec38968 --out-dir /home/er20605/tmp/foo/target/release/deps -C strip=debuginfo -L dependency=/home/er20605/tmp/foo/target/release/deps --extern hash32=/home/er20605/tmp/foo/target/release/deps/libhash32-dac718cb5492bd62.rmeta --extern stable_deref_trait=/home/er20605/tmp/foo/target/release/deps/libstable_deref_trait-61e4df8b11014761.rmeta --cap-lints allow --check-cfg 'cfg(arm_llsc)' --check-cfg 'cfg(has_atomic_load_store)'` (exit status: 101)

[lqd]

I believe this was fixed a few releases ago already. Updating your compiler from 1.86 to the slightly less old 1.87 should already fix it.

I'll look for the PR that fixed it, it could have been unintentional.

[lqd]

This was fixed by #139025, so this issue is a duplicate of #138979, closing it as such.

As I said above, updating your compiler will fix the ICE. Thanks for opening an issue!

[simpsoneric]

Wow, thank you for such a quick and helpful response.
Update fixed the issue.