rust-lang / rust-lang/rust

ICE: `encountered a fresh type during canonicalization`

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Since Nov 7, 2025.

A-dyn-trait C-bug F-min_generic_const_args I-ICE S-bug-has-test S-has-mcve T-compiler
Dominant language
Rust
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Description

Code
#![feature(associated_const_equality)]

trait B<C> {}
trait D<C, E>: B<C> + B<E> {
    fn f(&self) {}
}

trait Project {
    const SELF: dyn D<Self, Self>;
}

fn take1(_: Project<SELF = { loop {} }>) {}

fn main() {}

A mutant of glacier2's fixed/123140.rs

Meta

rustc --version --verbose:

rustc 1.93.0-nightly (c90bcb957 2025-11-06)
binary: rustc
commit-hash: c90bcb9571b7aab0d8beaa2ce8a998ffaf079d38
commit-date: 2025-11-06
host: x86_64-apple-darwin
release: 1.93.0-nightly
LLVM version: 21.1.3
Error output

Command: rustc

warning: trait objects without an explicit `dyn` are deprecated
  --> 10.rs:12:13
   |
12 | fn take1(_: Project<SELF = { loop {} }>) {}
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
   = note: for more information, see <https://doc.rust-lang.org/edition-guide/rust-2021/warnings-promoted-to-error.html>
   = note: `#[warn(bare_trait_objects)]` (part of `#[warn(rust_2021_compatibility)]`) on by default
help: if this is a dyn-compatible trait, use `dyn`
   |
12 | fn take1(_: dyn Project<SELF = { loop {} }>) {}
   |             +++

error[E0038]: the trait `Project` is not dyn compatible
  --> 10.rs:12:13
   |
12 | fn take1(_: Project<SELF = { loop {} }>) {}
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Project` is not dyn compatible
   |
note: for a trait to be dyn compatible it needs to allow building a vtable
      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
  --> 10.rs:9:11
   |
 8 | trait Project {
   |       ------- this trait is not dyn compatible...
 9 |     const SELF: dyn D<Self, Self>;
   |           ^^^^ ...because it contains this associated `const`
   = help: consider moving `SELF` to another trait

error[E0277]: the size for values of type `(dyn Project + 'static)` cannot be known at compilation time
  --> 10.rs:12:13
   |
12 | fn take1(_: Project<SELF = { loop {} }>) {}
   |             ^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `(dyn Project + 'static)`
   = help: unsized fn params are gated as an unstable feature
help: you can use `impl Trait` as the argument type
   |
12 | fn take1(_: impl Project<SELF = { loop {} }>) {}
   |             ++++
help: function arguments must have a statically known size, borrowed types always have a known size
   |
12 | fn take1(_: &dyn Project<SELF = { loop {} }>) {}
   |             ++++

error: internal compiler error: compiler/rustc_infer/src/infer/canonical/canonicalizer.rs:382:17: encountered a fresh type during canonicalization


thread 'rustc' (6386688) panicked at compiler/rustc_infer/src/infer/canonical/canonicalizer.rs:382:17:
Box<dyn Any>
Backtrace 

thread 'rustc' (6386688) panicked at compiler/rustc_infer/src/infer/canonical/canonicalizer.rs:382:17:
Box<dyn Any>
stack backtrace:
   0: std::panicking::begin_panic::<rustc_errors::ExplicitBug>
   1: <rustc_errors::diagnostic::BugAbort as rustc_errors::diagnostic::EmissionGuarantee>::emit_producing_guarantee
   2: rustc_middle::util::bug::opt_span_bug_fmt::<rustc_span::span_encoding::Span>::{closure#0}
   3: rustc_middle::ty::context::tls::with_opt::<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}
   4: rustc_middle::ty::context::tls::with_context_opt::<rustc_middle::ty::context::tls::with_opt<rustc_middle::util::bug::opt_span_bug_fmt<rustc_span::span_encoding::Span>::{closure#0}, !>::{closure#0}, !>
   5: rustc_middle::util::bug::bug_fmt
   6: <rustc_infer::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir::fold::TypeFolder<rustc_middle::ty::context::TyCtxt>>::fold_ty
   7: <&rustc_middle::ty::list::RawList<(), rustc_middle::ty::generic_args::GenericArg> as rustc_type_ir::fold::TypeFoldable<rustc_middle::ty::context::TyCtxt>>::fold_with::<rustc_infer::infer::canonical::canonicalizer::Canonicalizer>
   8: rustc_middle::ty::util::fold_list::<rustc_infer::infer::canonical::canonicalizer::Canonicalizer, &rustc_middle::ty::list::RawList<(), rustc_type_ir::binder::Binder<rustc_middle::ty::context::TyCtxt, rustc_type_ir::predicate::ExistentialPredicate<rustc_middle::ty::context::TyCtxt>>>, rustc_type_ir::binder::Binder<rustc_middle::ty::context::TyCtxt, rustc_type_ir::predicate::ExistentialPredicate<rustc_middle::ty::context::TyCtxt>>, <&rustc_middle::ty::list::RawList<(), rustc_type_ir::binder::Binder<rustc_middle::ty::context::TyCtxt, rustc_type_ir::predicate::ExistentialPredicate<rustc_middle::ty::context::TyCtxt>>> as rustc_type_ir::fold::TypeFoldable<rustc_middle::ty::context::TyCtxt>>::fold_with<rustc_infer::infer::canonical::canonicalizer::Canonicalizer>::{closure#0}>
   9: <rustc_infer::infer::canonical::canonicalizer::Canonicalizer as rustc_type_ir::fold::TypeFolder<rustc_middle::ty::context::TyCtxt>>::fold_ty
  10: <rustc_middle::ty::ParamEnvAnd<rustc_middle::traits::query::type_op::ImpliedOutlivesBounds> as rustc_trait_selection::traits::query::type_op::TypeOp>::fully_perform
  11: <rustc_borrowck::type_check::free_region_relations::UniversalRegionRelationsBuilder>::add_implied_bounds
  12: rustc_borrowck::type_check::type_check
  13: <rustc_borrowck::root_cx::BorrowCheckRootCtxt>::do_mir_borrowck
  14: rustc_borrowck::mir_borrowck
      [... omitted 1 frame ...]
  15: <rustc_middle::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
  16: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  17: rustc_interface::passes::create_and_enter_global_ctxt::<core::option::Option<rustc_interface::queries::Linker>, rustc_driver_impl::run_compiler::{closure#0}::{closure#2}>
  18: 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.

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 `/Users/jb/Library/CloudStorage/Dropbox/Desk/2503_rustc_ice/20251106 ice 보고용/rustc-ice-2025-11-07T06_32_36-88044.txt` to your bug report

query stack during panic:
#0 [mir_borrowck] borrow-checking `take1::{constant#0}`
#1 [analysis] running analysis passes on crate `10`
end of query stack
error: aborting due to 3 previous errors; 1 warning emitted

Some errors have detailed explanations: E0038, E0277.
For more information about an error, try `rustc --explain E0038`.

Notes

@rustbot label +F-associated_const_equality

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