rust-lang / rust-lang/rust

[ICE]: `expected projection ty, found ProjectionConst`

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C-bug F-field_projections F-generic_const_args F-min_generic_const_args I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

#![feature(generic_const_args)]

use std::field::{field_of, Field};
struct Struct {
    b: i64,
}
fn project_ref() {
    <field_of!(Struct, b)>::OFFSET;
}

original:

#![feature(generic_const_args, min_generic_const_args)]
#![feature(field_projections)]
use std::field::{field_of, Field};
struct Struct {
    b: i64,
}
fn project_ref() {
    <field_of!(Struct, b)>::OFFSET;
}

fn main() {}

Version information

rustc 1.100.0-nightly (0f819a160 2026-09-05)
binary: rustc
commit-hash: 0f819a1602c3814642aa63799b43772b7bb456e8
commit-date: 2026-09-05
host: x86_64-unknown-linux-gnu
release: 1.100.0-nightly
LLVM version: 23.1.1

Possibly related line of code:
https://github.com/rust-lang/rust/blob/0f819a1602c3814642aa63799b43772b7bb456e8/compiler/rustc_type_ir/src/term_kind.rs#L249-L261

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

Program output 

error[E0658]: use of unstable library feature `field_projections`
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:8:6
  |
8 |     <field_of!(Struct, b)>::OFFSET;
  |      ^^^^^^^^
  |
  = note: see issue #145383 <https://github.com/rust-lang/rust/issues/145383> for more information
  = help: add `#![feature(field_projections)]` to the crate attributes to enable
  = note: this compiler was built on 2026-09-05; consider upgrading it if it is out of date

error: `generic_const_args` requires `min_generic_const_args` to be enabled
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:1:12
  |
1 | #![feature(generic_const_args)]
  |            ^^^^^^^^^^^^^^^^^^
  |
  = help: enable all of these features

warning: the feature `generic_const_args` is incomplete and may not be safe to use and/or cause compiler crashes
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:1:12
  |
1 | #![feature(generic_const_args)]
  |            ^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #151972 <https://github.com/rust-lang/rust/issues/151972> for more information
  = note: `#[warn(incomplete_features)]` on by default

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:9:2
  |
9 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs`

error[E0658]: use of unstable library feature `field_projections`
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:3:18
  |
3 | use std::field::{field_of, Field};
  |                  ^^^^^^^^
  |
  = note: see issue #145383 <https://github.com/rust-lang/rust/issues/145383> for more information
  = help: add `#![feature(field_projections)]` to the crate attributes to enable
  = note: this compiler was built on 2026-09-05; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature `field_projections`
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:3:28
  |
3 | use std::field::{field_of, Field};
  |                            ^^^^^
  |
  = note: see issue #145383 <https://github.com/rust-lang/rust/issues/145383> for more information
  = help: add `#![feature(field_projections)]` to the crate attributes to enable
  = note: this compiler was built on 2026-09-05; consider upgrading it if it is out of date

error[E0658]: use of unstable library feature `field_projections`
 --> /tmp/icemaker_global_tempdir.mrZypDRoD1TV/rustc_testrunner_tmpdir_reporting.n04So9CIWbu4/mvce.rs:8:5
  |
8 |     <field_of!(Struct, b)>::OFFSET;
  |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  |
  = note: see issue #145383 <https://github.com/rust-lang/rust/issues/145383> for more information
  = help: add `#![feature(field_projections)]` to the crate attributes to enable
  = note: this compiler was built on 2026-09-05; consider upgrading it if it is out of date


thread 'rustc' (1264110) panicked at /rustc-dev/0f819a1602c3814642aa63799b43772b7bb456e8/compiler/rustc_type_ir/src/term_kind.rs:255:21:
expected projection ty, found ProjectionConst { def_id: DefId(2:4308 ~ core[d997]::field::Field::OFFSET) }
stack backtrace:
   0:     0x7f65b3ac54e6 - <<std[739b682464b2cb4f]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[d997ca8b291862e0]::fmt::Display>::fmt
   1:     0x7f65b420ba4f - core[d997ca8b291862e0]::fmt::write
   2:     0x7f65b3ada5cc - <std[739b682464b2cb4f]::sys::stdio::unix::Stderr as core[d997ca8b291862e0]::io::write::Write>::write_fmt
   3:     0x7f65b3a97d8a - std[739b682464b2cb4f]::panicking::default_hook::{closure#0}
   4:     0x7f65b3ab97e3 - std[739b682464b2cb4f]::panicking::default_hook
   5:     0x7f65b2a0943f - std[739b682464b2cb4f]::panicking::update_hook::<alloc[cfd194cf86e92e23]::boxed::Box<rustc_driver_impl[4b133f65db23c9ab]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f65b3ab9c82 - std[739b682464b2cb4f]::panicking::panic_with_hook
   7:     0x7f65b3a97e42 - std[739b682464b2cb4f]::panicking::panic_handler::{closure#0}
   8:     0x7f65b3a8ecb9 - std[739b682464b2cb4f]::sys::backtrace::__rust_end_short_backtrace::<std[739b682464b2cb4f]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f65b3a99a1d - __rustc[e7cd4045d256b0b7]::rust_begin_unwind
  10:     0x7f65b085c07c - core[d997ca8b291862e0]::panicking::panic_fmt
  11:     0x7f65b398cab3 - <rustc_type_ir[f404c092d65f65af]::predicate::NormalizesTo<rustc_middle[d333a51e0864de4]::ty::context::TyCtxt> as rustc_next_trait_solver[9898bcd21f45566e]::solve::assembly::GoalKind<rustc_trait_selection[c74f370ff3979d8d]::solve::delegate::SolverDelegate, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::consider_builtin_field_candidate
  12:     0x7f65b51ecfb4 - <rustc_next_trait_solver[9898bcd21f45566e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c74f370ff3979d8d]::solve::delegate::SolverDelegate, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::assemble_and_evaluate_candidates::<rustc_type_ir[f404c092d65f65af]::predicate::NormalizesTo<rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>
  13:     0x7f65b5211cb7 - <rustc_type_ir[f404c092d65f65af]::search_graph::SearchGraph<rustc_next_trait_solver[9898bcd21f45566e]::solve::search_graph::SearchGraphDelegate<rustc_trait_selection[c74f370ff3979d8d]::solve::delegate::SolverDelegate>, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::evaluate_goal::{closure#0}
  14:     0x7f65b51f7eae - <rustc_next_trait_solver[9898bcd21f45566e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c74f370ff3979d8d]::solve::delegate::SolverDelegate, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::evaluate_goal_raw
  15:     0x7f65b500b8bd - <rustc_next_trait_solver[9898bcd21f45566e]::solve::eval_ctxt::EvalCtxt<rustc_trait_selection[c74f370ff3979d8d]::solve::delegate::SolverDelegate, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::evaluate_goal_no_fast_paths
  16:     0x7f65b4ef2de4 - <rustc_next_trait_solver[9898bcd21f45566e]::normalize::NormalizationFolder<rustc_infer[6d73867ab5578060]::infer::InferCtxt, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt, rustc_trait_selection[c74f370ff3979d8d]::solve::normalize::normalize_with_universes<rustc_middle[d333a51e0864de4]::ty::generic_args::GenericArg>::{closure#0}>>::normalize_alias_term
  17:     0x7f65b4ef21b7 - <rustc_next_trait_solver[9898bcd21f45566e]::normalize::NormalizationFolder<rustc_infer[6d73867ab5578060]::infer::InferCtxt, rustc_middle[d333a51e0864de4]::ty::context::TyCtxt, rustc_trait_selection[c74f370ff3979d8d]::solve::normalize::normalize_with_universes<rustc_middle[d333a51e0864de4]::ty::generic_args::GenericArg>::{closure#0}> as rustc_type_ir[f404c092d65f65af]::fold::FallibleTypeFolder<rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::try_fold_const::{closure#0}
  18:     0x7f65b4eee2f1 - <rustc_traits[a12678c46138d38]::normalize_erasing_regions::provide::{closure#0} as core[d997ca8b291862e0]::ops::function::FnOnce<(rustc_middle[d333a51e0864de4]::ty::context::TyCtxt, rustc_middle[d333a51e0864de4]::ty::PseudoCanonicalInput<rustc_middle[d333a51e0864de4]::ty::generic_args::GenericArg>)>>::call_once
  19:     0x7f65b508bc2d - rustc_query_impl[483fff85713b0294]::execution::try_execute_query::<rustc_middle[d333a51e0864de4]::query::caches::DefaultCache<rustc_middle[d333a51e0864de4]::ty::PseudoCanonicalInput<rustc_middle[d333a51e0864de4]::ty::generic_args::GenericArg>, rustc_middle[d333a51e0864de4]::query::erase::ErasedData<[u8; 8usize]>>, false>
  20:     0x7f65b508b8e0 - rustc_query_impl[483fff85713b0294]::query_vtables::try_normalize_generic_arg_after_erasing_regions::execute_query_non_incr::__rust_end_short_backtrace
  21:     0x7f65b1082603 - <rustc_middle[d333a51e0864de4]::ty::normalize_erasing_regions::TryNormalizeAfterErasingRegionsFolder as rustc_type_ir[f404c092d65f65af]::fold::FallibleTypeFolder<rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>>::try_fold_const
  22:     0x7f65b108e85a - <rustc_mir_transform[d10c2acd6b2c0e17]::post_analysis_normalize::PostAnalysisNormalize as rustc_mir_transform[d10c2acd6b2c0e17]::pass_manager::MirPass>::run_pass
  23:     0x7f65b42181a1 - rustc_mir_transform[d10c2acd6b2c0e17]::run_analysis_to_runtime_passes
  24:     0x7f65b4bda0e9 - rustc_mir_transform[d10c2acd6b2c0e17]::mir_drops_elaborated_and_const_checked
  25:     0x7f65b48c3535 - rustc_query_impl[483fff85713b0294]::execution::try_execute_query::<rustc_data_structures[5e241a68fe1f0d9f]::vec_cache::VecCache<rustc_span[e9d5129d271bd047]::def_id::LocalDefId, rustc_middle[d333a51e0864de4]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[d333a51e0864de4]::dep_graph::graph::DepNodeIndex>, false>
  26:     0x7f65b48c306b - rustc_query_impl[483fff85713b0294]::query_vtables::mir_drops_elaborated_and_const_checked::execute_query_non_incr::__rust_end_short_backtrace
  27:     0x7f65b48c5e6e - <rustc_middle[d333a51e0864de4]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[69481172a0b187c3]::passes::run_required_analyses::{closure#2}::{closure#0}>::{closure#0}
  28:     0x7f65b48c4fcc - rustc_interface[69481172a0b187c3]::passes::analysis
  29:     0x7f65b53dc9ca - rustc_query_impl[483fff85713b0294]::execution::try_execute_query::<rustc_middle[d333a51e0864de4]::query::caches::SingleCache<rustc_middle[d333a51e0864de4]::query::erase::ErasedData<[u8; 0usize]>>, false>
  30:     0x7f65b53dc753 - rustc_query_impl[483fff85713b0294]::query_vtables::analysis::execute_query_non_incr::__rust_end_short_backtrace
  31:     0x7f65b559eae4 - rustc_interface[69481172a0b187c3]::interface::run_compiler::<(), rustc_driver_impl[4b133f65db23c9ab]::run_compiler::{closure#0}>::{closure#2}
  32:     0x7f65b5603164 - std[739b682464b2cb4f]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[69481172a0b187c3]::util::run_in_thread_with_globals<rustc_interface[69481172a0b187c3]::util::run_in_thread_pool_with_globals<rustc_interface[69481172a0b187c3]::interface::run_compiler<(), rustc_driver_impl[4b133f65db23c9ab]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  33:     0x7f65b5602f0b - <std[739b682464b2cb4f]::thread::lifecycle::spawn_unchecked<rustc_interface[69481172a0b187c3]::util::run_in_thread_with_globals<rustc_interface[69481172a0b187c3]::util::run_in_thread_pool_with_globals<rustc_interface[69481172a0b187c3]::interface::run_compiler<(), rustc_driver_impl[4b133f65db23c9ab]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[d997ca8b291862e0]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  34:     0x7f65b5600947 - <std[739b682464b2cb4f]::sys::thread::unix::Thread>::new::thread_start
  35:     0x7f65ae6980a2 - <unknown>
  36:     0x7f65ae72080c - <unknown>
  37:                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 1.100.0-nightly (0f819a160 2026-09-05) running on x86_64-unknown-linux-gnu

query stack during panic:
#0 [try_normalize_generic_arg_after_erasing_regions] normalizing `<field_of!(Struct, b) as core::field::Field>::OFFSET`
#1 [mir_drops_elaborated_and_const_checked] elaborating drops for `project_ref`
#2 [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: E0601, E0658.
For more information about an error, try `rustc --explain E0601`.

@rustbot label +F-generic_const_args +F-min_generic_const_args +F-field_projections

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

Start by compiling the reduced a.rs reproducer with the listed nightly toolchain and read compiler/rustc_type_ir/src/term_kind.rs around lines 249-261. Trace the panic through consider_builtin_field_candidate and the normalization path shown in the backtrace; done means the reproducer no longer causes an internal compiler error and has regression coverage.

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
Active
Clarity
Mostly clear
Newbie friendliness
48/100

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