rust-lang / rust-lang/rust

[ICE]: `prepare_vtable_segments()` is `None`

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Since Mar 4, 2026.

C-bug I-ICE S-bug-has-test S-has-mcve T-compiler WG-trait-system-refactor
Dominant language
Rust
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Description

auto-reduced (treereduce-rust):

//@compile-flags: -Znext-solver=globally
trait Foo: Bar<T> + Bar<u32> {}
trait Bar<T> {
    fn bar(self) -> T;
}

fn test_infer_version(x: &dyn Foo) {
    x.bar()
}

original:

trait Foo: Bar<T> + Bar<u32> {}
trait Bar<T> {
    fn bar(self) -> T;
}

fn test_infer_version(x: &dyn Foo) {
    x.bar()
}

fn main() {}

Version information

rustc 1.96.0-nightly (d2218f5f5 2026-03-03)
binary: rustc
commit-hash: d2218f5f5ca3f502772ec4cb69fc2ee44e096512
commit-date: 2026-03-03
host: x86_64-unknown-linux-gnu
release: 1.96.0-nightly
LLVM version: 22.1.0

Possibly related line of code:
https://github.com/rust-lang/rust/blob/d2218f5f5ca3f502772ec4cb69fc2ee44e096512/compiler/rustc_trait_selection/src/traits/vtable.rs#L362-L374

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Znext-solver=globally

Program output 

error[E0425]: cannot find type `T` in this scope
 --> /tmp/icemaker_global_tempdir.P6C3K8M8uTzI/rustc_testrunner_tmpdir_reporting.XSHvcksJG6gN/mvce.rs:1:16
  |
1 | trait Foo: Bar<T> + Bar<u32> {}
  |                ^ not found in this scope

error[E0601]: `main` function not found in crate `mvce`
 --> /tmp/icemaker_global_tempdir.P6C3K8M8uTzI/rustc_testrunner_tmpdir_reporting.XSHvcksJG6gN/mvce.rs:8:2
  |
8 | }
  |  ^ consider adding a `main` function to `/tmp/icemaker_global_tempdir.P6C3K8M8uTzI/rustc_testrunner_tmpdir_reporting.XSHvcksJG6gN/mvce.rs`


thread 'rustc' (833187) panicked at /rustc-dev/d2218f5f5ca3f502772ec4cb69fc2ee44e096512/compiler/rustc_trait_selection/src/traits/vtable.rs:368:77:
called `Option::unwrap()` on a `None` value
stack backtrace:
   0:     0x7f1e84b62aab - <<std[76599d2169901dc8]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[d5ffb84325ed5c2a]::fmt::Display>::fmt
   1:     0x7f1e852228c8 - core[d5ffb84325ed5c2a]::fmt::write
   2:     0x7f1e84b79ab6 - <std[76599d2169901dc8]::sys::stdio::unix::Stderr as std[76599d2169901dc8]::io::Write>::write_fmt
   3:     0x7f1e84b38b88 - std[76599d2169901dc8]::panicking::default_hook::{closure#0}
   4:     0x7f1e84b55f13 - std[76599d2169901dc8]::panicking::default_hook
   5:     0x7f1e83b424cc - std[76599d2169901dc8]::panicking::update_hook::<alloc[f847baa7d3d2ac55]::boxed::Box<rustc_driver_impl[ffd722fd6c32666a]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f1e84b561f2 - std[76599d2169901dc8]::panicking::panic_with_hook
   7:     0x7f1e84b38c7a - std[76599d2169901dc8]::panicking::panic_handler::{closure#0}
   8:     0x7f1e84b2f979 - std[76599d2169901dc8]::sys::backtrace::__rust_end_short_backtrace::<std[76599d2169901dc8]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f1e84b3a6ad - __rustc[7dea9537d06e225e]::rust_begin_unwind
  10:     0x7f1e8171975c - core[d5ffb84325ed5c2a]::panicking::panic_fmt
  11:     0x7f1e81202052 - core[d5ffb84325ed5c2a]::panicking::panic
  12:     0x7f1e8190ca29 - core[d5ffb84325ed5c2a]::option::unwrap_failed
  13:     0x7f1e861fca2d - rustc_trait_selection[502c21a12406236f]::traits::vtable::first_method_vtable_slot
  14:     0x7f1e862006b2 - rustc_query_impl[89f9236b2ac04da0]::execution::try_execute_query::<rustc_middle[7c9cbe436035c5a4]::query::caches::DefaultCache<rustc_type_ir[6a4b9ee69e1ff834]::predicate::TraitRef<rustc_middle[7c9cbe436035c5a4]::ty::context::TyCtxt>, rustc_middle[7c9cbe436035c5a4]::query::erase::ErasedData<[u8; 8usize]>>, false>
  15:     0x7f1e862003dd - rustc_query_impl[89f9236b2ac04da0]::query_impl::first_method_vtable_slot::execute_query_non_incr::__rust_end_short_backtrace
  16:     0x7f1e854cf3ed - rustc_ty_utils[23782f25fc8ac972]::instance::resolve_instance_raw
  17:     0x7f1e854cb8df - rustc_query_impl[89f9236b2ac04da0]::query_impl::resolve_instance_raw::invoke_provider_fn::__rust_begin_short_backtrace
  18:     0x7f1e854ca99c - rustc_query_impl[89f9236b2ac04da0]::execution::try_execute_query::<rustc_middle[7c9cbe436035c5a4]::query::caches::DefaultCache<rustc_middle[7c9cbe436035c5a4]::ty::PseudoCanonicalInput<(rustc_span[8a71b77c74bc13cb]::def_id::DefId, &rustc_middle[7c9cbe436035c5a4]::ty::list::RawList<(), rustc_middle[7c9cbe436035c5a4]::ty::generic_args::GenericArg>)>, rustc_middle[7c9cbe436035c5a4]::query::erase::ErasedData<[u8; 32usize]>>, false>
  19:     0x7f1e854ca5c3 - rustc_query_impl[89f9236b2ac04da0]::query_impl::resolve_instance_raw::execute_query_non_incr::__rust_end_short_backtrace
  20:     0x7f1e855a97a2 - <rustc_middle[7c9cbe436035c5a4]::ty::instance::Instance>::try_resolve
  21:     0x7f1e855a5892 - <rustc_mir_transform[c7b522523fe3a5eb]::check_call_recursion::CheckCallRecursion as rustc_mir_transform[c7b522523fe3a5eb]::pass_manager::MirLint>::run_lint
  22:     0x7f1e8520b72d - rustc_mir_transform[c7b522523fe3a5eb]::mir_built
  23:     0x7f1e8536d18a - rustc_query_impl[89f9236b2ac04da0]::execution::try_execute_query::<rustc_data_structures[79f5f180de225010]::vec_cache::VecCache<rustc_span[8a71b77c74bc13cb]::def_id::LocalDefId, rustc_middle[7c9cbe436035c5a4]::query::erase::ErasedData<[u8; 8usize]>, rustc_middle[7c9cbe436035c5a4]::dep_graph::graph::DepNodeIndex>, false>
  24:     0x7f1e8536cc83 - rustc_query_impl[89f9236b2ac04da0]::query_impl::mir_built::execute_query_non_incr::__rust_end_short_backtrace
  25:     0x7f1e81fb926c - rustc_mir_build[10e3059a1c65a42d]::check_unsafety::check_unsafety
  26:     0x7f1e8536b99f - rustc_query_impl[89f9236b2ac04da0]::execution::try_execute_query::<rustc_data_structures[79f5f180de225010]::vec_cache::VecCache<rustc_span[8a71b77c74bc13cb]::def_id::LocalDefId, rustc_middle[7c9cbe436035c5a4]::query::erase::ErasedData<[u8; 0usize]>, rustc_middle[7c9cbe436035c5a4]::dep_graph::graph::DepNodeIndex>, false>
  27:     0x7f1e8536b6f6 - rustc_query_impl[89f9236b2ac04da0]::query_impl::check_unsafety::execute_query_non_incr::__rust_end_short_backtrace
  28:     0x7f1e8536a9ea - <rustc_middle[7c9cbe436035c5a4]::ty::context::TyCtxt>::par_hir_body_owners::<rustc_interface[400bc27e64bfd912]::passes::run_required_analyses::{closure#1}::{closure#0}>::{closure#0}
  29:     0x7f1e8536a02f - rustc_interface[400bc27e64bfd912]::passes::analysis
  30:     0x7f1e8643175c - rustc_query_impl[89f9236b2ac04da0]::execution::try_execute_query::<rustc_middle[7c9cbe436035c5a4]::query::caches::SingleCache<rustc_middle[7c9cbe436035c5a4]::query::erase::ErasedData<[u8; 0usize]>>, false>
  31:     0x7f1e864314bb - rustc_query_impl[89f9236b2ac04da0]::query_impl::analysis::execute_query_non_incr::__rust_end_short_backtrace
  32:     0x7f1e863eda2d - rustc_interface[400bc27e64bfd912]::interface::run_compiler::<(), rustc_driver_impl[ffd722fd6c32666a]::run_compiler::{closure#0}>::{closure#1}
  33:     0x7f1e863d20be - std[76599d2169901dc8]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[400bc27e64bfd912]::util::run_in_thread_with_globals<rustc_interface[400bc27e64bfd912]::util::run_in_thread_pool_with_globals<rustc_interface[400bc27e64bfd912]::interface::run_compiler<(), rustc_driver_impl[ffd722fd6c32666a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  34:     0x7f1e863d2720 - <std[76599d2169901dc8]::thread::lifecycle::spawn_unchecked<rustc_interface[400bc27e64bfd912]::util::run_in_thread_with_globals<rustc_interface[400bc27e64bfd912]::util::run_in_thread_pool_with_globals<rustc_interface[400bc27e64bfd912]::interface::run_compiler<(), rustc_driver_impl[ffd722fd6c32666a]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[d5ffb84325ed5c2a]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  35:     0x7f1e863d35ac - <std[76599d2169901dc8]::sys::thread::unix::Thread>::new::thread_start
  36:     0x7f1e7fe5998b - <unknown>
  37:     0x7f1e7fedda0c - <unknown>
  38:                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 1.96.0-nightly (d2218f5f5 2026-03-03) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z next-solver=globally -Z dump-mir-dir=dir

query stack during panic:
#0 [first_method_vtable_slot] finding the slot within the vtable of `dyn Foo` for the implementation of `Bar`
#1 [resolve_instance_raw] resolving instance `<dyn Foo as Bar<()>>::bar`
#2 [mir_built] building MIR for `test_infer_version`
#3 [check_unsafety] unsafety-checking `test_infer_version`
#4 [analysis] running analysis passes on crate `mvce`
end of query stack
error: aborting due to 2 previous errors

Some errors have detailed explanations: E0425, E0601.
For more information about an error, try `rustc --explain E0425`.

@rustbot label +WG-trait-system-refactor

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