[ICE]: `enum variant discr was too generic to eval`
Open
Nobody has claimed this yet.
C-bug
I-ICE
S-bug-has-test
S-has-mcve
T-compiler
- Dominant language
- Rust
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- 119k
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Description
auto-reduced (treereduce-rust):
#![feature(const_async_blocks)]
enum Foo {
Bar = (|| yield, 2).1,
}
original:
#![feature(coroutines)]
#![feature(const_async_blocks)]
#![feature(yield_expr)]
enum Foo {
Bar = (
#[coroutine]
|| yield,
2,
)
.1,
}
fn main() {}
Version information
rustc 1.98.0-nightly (ea088e0a3 2026-07-05)
binary: rustc
commit-hash: ea088e0a3dd50c494b4589c3c121d7469dceec8f
commit-date: 2026-07-05
host: x86_64-unknown-linux-gnu
release: 1.98.0-nightly
LLVM version: 22.1.8
Possibly related line of code:
https://github.com/rust-lang/rust/blob/ea088e0a3dd50c494b4589c3c121d7469dceec8f/compiler/rustc_hir_analysis/src/check/wfcheck.rs#L1132-L1144
Command:
/home/matthias/.rustup/toolchains/master/bin/rustc
Program output
error[E0658]: yield syntax is experimental
--> /tmp/icemaker_global_tempdir.ptA2QDVmn15G/rustc_testrunner_tmpdir_reporting.L6CW6WUYm6Fw/mvce.rs:4:15
|
4 | Bar = (|| yield, 2).1,
| ^^^^^
|
= note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
= help: add `#![feature(yield_expr)]` to the crate attributes to enable
= note: this compiler was built on 2026-07-05; consider upgrading it if it is out of date
error[E0658]: yield syntax is experimental
--> /tmp/icemaker_global_tempdir.ptA2QDVmn15G/rustc_testrunner_tmpdir_reporting.L6CW6WUYm6Fw/mvce.rs:4:15
|
4 | Bar = (|| yield, 2).1,
| ^^^^^
|
= note: see issue #43122 <https://github.com/rust-lang/rust/issues/43122> for more information
= help: add `#![feature(yield_expr)]` to the crate attributes to enable
= note: this compiler was built on 2026-07-05; consider upgrading it if it is out of date
error: `yield` can only be used in `#[coroutine]` closures, or `gen` blocks
--> /tmp/icemaker_global_tempdir.ptA2QDVmn15G/rustc_testrunner_tmpdir_reporting.L6CW6WUYm6Fw/mvce.rs:4:15
|
4 | Bar = (|| yield, 2).1,
| ^^^^^
|
help: use `#[coroutine]` to make this closure a coroutine
|
4 | Bar = (#[coroutine] || yield, 2).1,
| ++++++++++++
error[E0601]: `main` function not found in crate `mvce`
--> /tmp/icemaker_global_tempdir.ptA2QDVmn15G/rustc_testrunner_tmpdir_reporting.L6CW6WUYm6Fw/mvce.rs:5:2
|
5 | }
| ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.ptA2QDVmn15G/rustc_testrunner_tmpdir_reporting.L6CW6WUYm6Fw/mvce.rs`
error: internal compiler error: /rustc-dev/ea088e0a3dd50c494b4589c3c121d7469dceec8f/compiler/rustc_hir_analysis/src/check/wfcheck.rs:1138:25: enum variant discr was too generic to eval
thread 'rustc' (2036952) panicked at /rustc-dev/ea088e0a3dd50c494b4589c3c121d7469dceec8f/compiler/rustc_hir_analysis/src/check/wfcheck.rs:1138:25:
Box<dyn Any>
stack backtrace:
0: 0x7fce060e5ea6 - <<std[1023ab8fe43ea5ab]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[ac254214b649f1de]::fmt::Display>::fmt
1: 0x7fce0680ecc8 - core[ac254214b649f1de]::fmt::write
2: 0x7fce060fb28c - <std[1023ab8fe43ea5ab]::sys::stdio::unix::Stderr as std[1023ab8fe43ea5ab]::io::Write>::write_fmt
3: 0x7fce060ba30a - std[1023ab8fe43ea5ab]::panicking::default_hook::{closure#0}
4: 0x7fce060d85f3 - std[1023ab8fe43ea5ab]::panicking::default_hook
5: 0x7fce050c45b8 - std[1023ab8fe43ea5ab]::panicking::update_hook::<alloc[e3e2338491c50a85]::boxed::Box<rustc_driver_impl[cdfcb04387bfb2d]::install_ice_hook::{closure#1}>>::{closure#0}
6: 0x7fce060d8a92 - std[1023ab8fe43ea5ab]::panicking::panic_with_hook
7: 0x7fce050f20e1 - std[1023ab8fe43ea5ab]::panicking::begin_panic::<rustc_errors[d242d9a7579ddf78]::ExplicitBug>::{closure#0}
8: 0x7fce050eae56 - std[1023ab8fe43ea5ab]::sys::backtrace::__rust_end_short_backtrace::<std[1023ab8fe43ea5ab]::panicking::begin_panic<rustc_errors[d242d9a7579ddf78]::ExplicitBug>::{closure#0}, !>
9: 0x7fce050e8e97 - std[1023ab8fe43ea5ab]::panicking::begin_panic::<rustc_errors[d242d9a7579ddf78]::ExplicitBug>
10: 0x7fce050fd271 - <rustc_errors[d242d9a7579ddf78]::diagnostic::BugAbort as rustc_errors[d242d9a7579ddf78]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
11: 0x7fce05649cdc - <rustc_errors[d242d9a7579ddf78]::DiagCtxtHandle>::span_bug::<rustc_span[1809dac9b9f9f1f9]::span_encoding::Span, alloc[e3e2338491c50a85]::string::String>
12: 0x7fce056787f6 - rustc_middle[65e93962a5a43da7]::util::bug::opt_span_bug_fmt::<rustc_span[1809dac9b9f9f1f9]::span_encoding::Span>::{closure#0}
13: 0x7fce05678982 - rustc_middle[65e93962a5a43da7]::ty::context::tls::with_opt::<rustc_middle[65e93962a5a43da7]::util::bug::opt_span_bug_fmt<rustc_span[1809dac9b9f9f1f9]::span_encoding::Span>::{closure#0}, !>::{closure#0}
14: 0x7fce056640cb - rustc_middle[65e93962a5a43da7]::ty::context::tls::with_context_opt::<rustc_middle[65e93962a5a43da7]::ty::context::tls::with_opt<rustc_middle[65e93962a5a43da7]::util::bug::opt_span_bug_fmt<rustc_span[1809dac9b9f9f1f9]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
15: 0x7fce030d0a68 - rustc_middle[65e93962a5a43da7]::util::bug::span_bug_fmt::<rustc_span[1809dac9b9f9f1f9]::span_encoding::Span>
16: 0x7fce070cbff7 - rustc_hir_analysis[6a1607dc5c50ec45]::check::wfcheck::check_type_defn
17: 0x7fce076b7164 - rustc_hir_analysis[6a1607dc5c50ec45]::check::check::check_item_type
18: 0x7fce076b03b0 - rustc_hir_analysis[6a1607dc5c50ec45]::check::wfcheck::check_well_formed
19: 0x7fce076b0391 - rustc_query_impl[e6cc49fff9d6167b]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
20: 0x7fce076af971 - rustc_query_impl[e6cc49fff9d6167b]::execution::try_execute_query::<rustc_data_structures[1a2aab4d02078da7]::vec_cache::VecCache<rustc_span[1809dac9b9f9f1f9]::def_id::LocalDefId, rustc_middle[65e93962a5a43da7]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[65e93962a5a43da7]::dep_graph::graph::DepNodeIndex>, false>
21: 0x7fce076af707 - rustc_query_impl[e6cc49fff9d6167b]::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
22: 0x7fce076ac185 - rustc_hir_analysis[6a1607dc5c50ec45]::check::wfcheck::check_type_wf
23: 0x7fce076ac093 - rustc_query_impl[e6cc49fff9d6167b]::query_impl::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
24: 0x7fce07985186 - rustc_query_impl[e6cc49fff9d6167b]::execution::try_execute_query::<rustc_middle[65e93962a5a43da7]::query::caches::SingleCache<rustc_middle[65e93962a5a43da7]::query::erase::ErasedData<[u8; 1usize]>>, false>
25: 0x7fce07984f69 - rustc_query_impl[e6cc49fff9d6167b]::query_impl::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
26: 0x7fce06bd6b9a - rustc_hir_analysis[6a1607dc5c50ec45]::check_crate
27: 0x7fce06bdb1ba - rustc_interface[a6d30ce4ed30ee91]::passes::analysis
28: 0x7fce07983707 - rustc_query_impl[e6cc49fff9d6167b]::execution::try_execute_query::<rustc_middle[65e93962a5a43da7]::query::caches::SingleCache<rustc_middle[65e93962a5a43da7]::query::erase::ErasedData<[u8; 0usize]>>, false>
29: 0x7fce07983369 - rustc_query_impl[e6cc49fff9d6167b]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
30: 0x7fce07959e40 - rustc_interface[a6d30ce4ed30ee91]::interface::run_compiler::<(), rustc_driver_impl[cdfcb04387bfb2d]::run_compiler::{closure#0}>::{closure#1}
31: 0x7fce0799227a - std[1023ab8fe43ea5ab]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[a6d30ce4ed30ee91]::util::run_in_thread_with_globals<rustc_interface[a6d30ce4ed30ee91]::util::run_in_thread_pool_with_globals<rustc_interface[a6d30ce4ed30ee91]::interface::run_compiler<(), rustc_driver_impl[cdfcb04387bfb2d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
32: 0x7fce0799202d - <std[1023ab8fe43ea5ab]::thread::lifecycle::spawn_unchecked<rustc_interface[a6d30ce4ed30ee91]::util::run_in_thread_with_globals<rustc_interface[a6d30ce4ed30ee91]::util::run_in_thread_pool_with_globals<rustc_interface[a6d30ce4ed30ee91]::interface::run_compiler<(), rustc_driver_impl[cdfcb04387bfb2d]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[ac254214b649f1de]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
33: 0x7fce07996450 - <std[1023ab8fe43ea5ab]::sys::thread::unix::Thread>::new::thread_start
34: 0x7fce012981b9 - <unknown>
35: 0x7fce0131d21c - <unknown>
36: 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 1.98.0-nightly (ea088e0a3 2026-07-05) running on x86_64-unknown-linux-gnu
query stack during panic:
#0 [check_well_formed] checking that `Foo` is well-formed
#1 [check_type_wf] checking that types are well-formed
#2 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 5 previous errors
Some errors have detailed explanations: E0601, E0658.
For more information about an error, try `rustc --explain E0601`.
@rustbot label +F-coroutines +F-const_async_blocks +F-yield_expr
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by compiling the reduced a.rs example with the referenced nightly toolchain and inspect compiler/rustc_hir_analysis/src/check/wfcheck.rs around lines 1132–1144, especially check_type_defn. Trace the check_well_formed query shown in the report and add regression coverage for this enum discriminant case. Done means the example no longer triggers the internal compiler error.
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
- 42/100