[ICE]: next solver: `Unexpected node Synthetic`
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@DAstapov is already working on this.
Since Jul 20, 2026.
C-bug
D-papercut
I-ICE
T-compiler
WG-trait-system-refactor
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Description
Code
this code compiles
//@compile-flags: -Znext-solver=globally --edition=2024
trait Foo: Mirror
where
<Self as Mirror>::Assoc: Clone,
{
async fn e() {}
}
trait Mirror {
type Assoc;
}
fn main() {}
but if we remove the first : Mirror annotation
//@compile-flags: -Znext-solver=globally --edition=2024
trait Foo
where
<Self as Mirror>::Assoc: Clone,
{
async fn e() {}
}
trait Mirror {
type Assoc;
}
fn main() {}
it will cause the next solver to ICE
Meta
rustc --version --verbose:
rustc 1.99.0-nightly (eff8269f7 2026-07-18)
binary: rustc
commit-hash: eff8269f797067c30555e77f160ec84c0ed15cd9
commit-date: 2026-07-18
host: x86_64-unknown-linux-gnu
release: 1.99.0-nightly
LLVM version: 22.1.8
Error output
error[E0277]: the trait bound `Self: Mirror` is not satisfied
--> code.rs:5:17
|
5 | async fn e() {}
| ^ the trait `Mirror` is not implemented for `Self`
|
help: consider further restricting `Self`
|
1 | trait Foo: Mirror /*: Mirror .*/
| ++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
--> code.rs:1:1
|
1 | trait Foo /*: Mirror .*/
| ^^^^^^^^^ the trait `Mirror` is not implemented for `Self`
|
help: consider further restricting `Self`
|
1 | trait Foo: Mirror /*: Mirror .*/
| ++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
--> code.rs:3:30
|
3 | <Self as Mirror>::Assoc: Clone,
| ^^^^^ the trait `Mirror` is not implemented for `Self`
|
note: required by a bound in `Clone`
--> /home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/clone.rs:194:24
|
194 | pub const trait Clone: Sized {
| ^^^^^ required by this bound in `Clone`
help: consider further restricting `Self`
|
1 | trait Foo: Mirror /*: Mirror .*/
| ++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
|
note: required by a bound in `Foo`
--> code.rs:3:30
|
1 | trait Foo /*: Mirror .*/
| --- required by a bound in this trait
2 | where
3 | <Self as Mirror>::Assoc: Clone,
| ^^^^^ required by this bound in `Foo`
help: consider further restricting `Self`
|
1 | trait Foo: Mirror /*: Mirror .*/
| ++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
--> code.rs:5:5
|
5 | async fn e() {}
| ^^^^^^^^^^^^ the trait `Mirror` is not implemented for `Self`
|
help: consider further restricting `Self`
|
5 | async fn e() where Self: Mirror {}
| ++++++++++++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
--> code.rs:3:30
|
3 | <Self as Mirror>::Assoc: Clone,
| ^^^^^ the trait `Mirror` is not implemented for `Self`
|
note: required by a bound in `Clone`
--> /home/matthias/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/clone.rs:194:24
|
194 | pub const trait Clone: Sized {
| ^^^^^ required by this bound in `Clone`
help: consider further restricting `Self`
|
5 | async fn e() where Self: Mirror {}
| ++++++++++++++++++
error[E0277]: the trait bound `Self: Mirror` is not satisfied
|
note: required by a bound in `Foo`
--> code.rs:3:30
|
1 | trait Foo /*: Mirror .*/
| --- required by a bound in this trait
2 | where
3 | <Self as Mirror>::Assoc: Clone,
| ^^^^^ required by this bound in `Foo`
help: consider further restricting `Self`
|
5 | async fn e() where Self: Mirror {}
| ++++++++++++++++++
error: the type `impl Future<Output = ()>` is not well-formed
--> code.rs:5:17
|
5 | async fn e() {}
| ^
Backtrace
error: internal compiler error: /rustc-dev/eff8269f797067c30555e77f160ec84c0ed15cd9/compiler/rustc_hir_analysis/src/hir_wf_check.rs:192:25: Unexpected node Synthetic
thread 'rustc' (1214808) panicked at /rustc-dev/eff8269f797067c30555e77f160ec84c0ed15cd9/compiler/rustc_hir_analysis/src/hir_wf_check.rs:192:25:
Box<dyn Any>
stack backtrace:
0: 0x7fc76ba50a16 - <<std[2a8c3cd46992084f]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[f0447a45d83adb47]::fmt::Display>::fmt
1: 0x7fc76c00ec88 - core[f0447a45d83adb47]::fmt::write
2: 0x7fc76ba65c7c - <std[2a8c3cd46992084f]::sys::stdio::unix::Stderr as core[f0447a45d83adb47]::io::write::Write>::write_fmt
3: 0x7fc76ba226aa - std[2a8c3cd46992084f]::panicking::default_hook::{closure#0}
4: 0x7fc76ba43143 - std[2a8c3cd46992084f]::panicking::default_hook
5: 0x7fc76a9fc04b - std[2a8c3cd46992084f]::panicking::update_hook::<alloc[4a894a599ddd1b2d]::boxed::Box<rustc_driver_impl[c2a64f8504684822]::install_ice_hook::{closure#1}>>::{closure#0}
6: 0x7fc76ba435e2 - std[2a8c3cd46992084f]::panicking::panic_with_hook
7: 0x7fc76aa29b01 - std[2a8c3cd46992084f]::panicking::begin_panic::<rustc_errors[1361c60ac6b93a37]::ExplicitBug>::{closure#0}
8: 0x7fc76aa229e6 - std[2a8c3cd46992084f]::sys::backtrace::__rust_end_short_backtrace::<std[2a8c3cd46992084f]::panicking::begin_panic<rustc_errors[1361c60ac6b93a37]::ExplicitBug>::{closure#0}, !>
9: 0x7fc76aa208b7 - std[2a8c3cd46992084f]::panicking::begin_panic::<rustc_errors[1361c60ac6b93a37]::ExplicitBug>
10: 0x7fc76aa34c91 - <rustc_errors[1361c60ac6b93a37]::diagnostic::BugAbort as rustc_errors[1361c60ac6b93a37]::diagnostic::EmissionGuarantee>::emit_producing_guarantee
11: 0x7fc76afc19e9 - rustc_middle[96c442875f2cb62c]::util::bug::opt_span_bug_fmt::<rustc_span[157f53c51de8f998]::span_encoding::Span>::{closure#0}
12: 0x7fc76afc1b52 - rustc_middle[96c442875f2cb62c]::ty::context::tls::with_opt::<rustc_middle[96c442875f2cb62c]::util::bug::opt_span_bug_fmt<rustc_span[157f53c51de8f998]::span_encoding::Span>::{closure#0}, !>::{closure#0}
13: 0x7fc76aface0b - rustc_middle[96c442875f2cb62c]::ty::context::tls::with_context_opt::<rustc_middle[96c442875f2cb62c]::ty::context::tls::with_opt<rustc_middle[96c442875f2cb62c]::util::bug::opt_span_bug_fmt<rustc_span[157f53c51de8f998]::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
14: 0x7fc7684e23d4 - rustc_middle[96c442875f2cb62c]::util::bug::bug_fmt
15: 0x7fc76ab9f885 - rustc_hir_analysis[e34517a71420646b]::hir_wf_check::diagnostic_hir_wf_check
16: 0x7fc76b4c110e - rustc_query_impl[5a309cdb9f26d392]::query_impl::diagnostic_hir_wf_check::invoke_provider_fn::__rust_begin_short_backtrace
17: 0x7fc76b4298b5 - rustc_query_impl[5a309cdb9f26d392]::execution::try_execute_query::<rustc_middle[96c442875f2cb62c]::query::caches::DefaultCache<(rustc_middle[96c442875f2cb62c]::ty::predicate::Predicate, rustc_middle[96c442875f2cb62c]::traits::WellFormedLoc), rustc_middle[96c442875f2cb62c]::query::erase::ErasedData<[u8; 8usize]>>, false>
18: 0x7fc76b4c12f0 - rustc_query_impl[5a309cdb9f26d392]::query_impl::diagnostic_hir_wf_check::execute_query_non_incr::__rust_end_short_backtrace
19: 0x7fc76b861bbc - <rustc_trait_selection[230890ec563485ea]::error_reporting::TypeErrCtxt>::report_selection_error
20: 0x7fc76b887d7b - <rustc_trait_selection[230890ec563485ea]::error_reporting::TypeErrCtxt>::report_fulfillment_error
21: 0x7fc76a30d47c - <rustc_trait_selection[230890ec563485ea]::error_reporting::TypeErrCtxt>::report_fulfillment_errors
22: 0x7fc76c95e1e3 - rustc_hir_analysis[e34517a71420646b]::check::wfcheck::enter_wf_checking_ctxt::<rustc_hir_analysis[e34517a71420646b]::check::wfcheck::check_associated_item::{closure#0}>
23: 0x7fc76c6ff4d3 - rustc_hir_analysis[e34517a71420646b]::check::wfcheck::check_trait_item
24: 0x7fc76caed030 - rustc_hir_analysis[e34517a71420646b]::check::check::check_item_type
25: 0x7fc76cae921c - rustc_hir_analysis[e34517a71420646b]::check::wfcheck::check_well_formed
26: 0x7fc76cae91ed - rustc_query_impl[5a309cdb9f26d392]::query_impl::check_well_formed::invoke_provider_fn::__rust_begin_short_backtrace
27: 0x7fc76cae87d3 - rustc_query_impl[5a309cdb9f26d392]::execution::try_execute_query::<rustc_data_structures[6044b2f767527520]::vec_cache::VecCache<rustc_span[157f53c51de8f998]::def_id::LocalDefId, rustc_middle[96c442875f2cb62c]::query::erase::ErasedData<[u8; 1usize]>, rustc_middle[96c442875f2cb62c]::dep_graph::graph::DepNodeIndex>, false>
28: 0x7fc76cae8553 - rustc_query_impl[5a309cdb9f26d392]::query_impl::check_well_formed::execute_query_non_incr::__rust_end_short_backtrace
29: 0x7fc76cae508a - rustc_hir_analysis[e34517a71420646b]::check::wfcheck::check_type_wf
30: 0x7fc76cae4f4f - rustc_query_impl[5a309cdb9f26d392]::query_impl::check_type_wf::invoke_provider_fn::__rust_begin_short_backtrace
31: 0x7fc76d148e92 - rustc_query_impl[5a309cdb9f26d392]::execution::try_execute_query::<rustc_middle[96c442875f2cb62c]::query::caches::SingleCache<rustc_middle[96c442875f2cb62c]::query::erase::ErasedData<[u8; 1usize]>>, false>
32: 0x7fc76d148c77 - rustc_query_impl[5a309cdb9f26d392]::query_impl::check_type_wf::execute_query_non_incr::__rust_end_short_backtrace
33: 0x7fc76c619c9a - rustc_hir_analysis[e34517a71420646b]::check_crate
34: 0x7fc76c614bf5 - rustc_interface[bb04609e4c960450]::passes::analysis
35: 0x7fc76d1474c7 - rustc_query_impl[5a309cdb9f26d392]::execution::try_execute_query::<rustc_middle[96c442875f2cb62c]::query::caches::SingleCache<rustc_middle[96c442875f2cb62c]::query::erase::ErasedData<[u8; 0usize]>>, false>
36: 0x7fc76d147129 - rustc_query_impl[5a309cdb9f26d392]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
37: 0x7fc76d10464d - rustc_interface[bb04609e4c960450]::interface::run_compiler::<(), rustc_driver_impl[c2a64f8504684822]::run_compiler::{closure#0}>::{closure#2}
38: 0x7fc76d172ae4 - std[2a8c3cd46992084f]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[bb04609e4c960450]::util::run_in_thread_with_globals<rustc_interface[bb04609e4c960450]::util::run_in_thread_pool_with_globals<rustc_interface[bb04609e4c960450]::interface::run_compiler<(), rustc_driver_impl[c2a64f8504684822]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
39: 0x7fc76d1728bb - <std[2a8c3cd46992084f]::thread::lifecycle::spawn_unchecked<rustc_interface[bb04609e4c960450]::util::run_in_thread_with_globals<rustc_interface[bb04609e4c960450]::util::run_in_thread_pool_with_globals<rustc_interface[bb04609e4c960450]::interface::run_compiler<(), rustc_driver_impl[c2a64f8504684822]::run_compiler::{closure#0}>::{closure#2}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[f0447a45d83adb47]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
40: 0x7fc76d17cec8 - <std[2a8c3cd46992084f]::sys::thread::unix::Thread>::new::thread_start
41: 0x7fc766a97739 - <unknown>
42: 0x7fc766b1bedc - <unknown>
43: 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: please attach the file at `/home/matthias/vcs/github/CRED/rustc-ice-2026-07-19T09_52_34-1214798.txt` to your bug report
note: rustc 1.99.0-nightly (eff8269f7 2026-07-18) running on x86_64-unknown-linux-gnu
note: compiler flags: -Z next-solver=globally
query stack during panic:
#0 [diagnostic_hir_wf_check] performing HIR wf-checking for predicate `Binder { value: WellFormed(Term::Ty(Alias(Yes, Alias { kind: Opaque { def_id: DefId(0:5 ~ code[b566]::Foo::e::{opaque#0}) }, args: [Self/#0], .. }))), bound_vars: [] }` at item `Ty(DefId(0:10 ~ code[b566]::Foo::e::{anon_assoc#0}))`
#1 [check_well_formed] checking that `Foo::e` is well-formed
#2 [check_type_wf] checking that types are well-formed
#3 [analysis] running analysis passes on crate `code`
end of query stack
error: aborting due to 9 previous errors
For more information about this error, try `rustc --explain E0277`.
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