rust-lang / rust-lang/rust

[ICE]: InterpErrorInfo(InterpErrorInfoInner { kind: UndefinedBehavior(ValidationError

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C-bug F-try_as_dyn I-ICE needs-triage T-compiler
Dominant language
Rust
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Description

snippet:

//@compile-flags: -Zmir-opt-level=5 -Zdump-mir=all -Zalways-encode-mir -Zextra-const-ub-checks
#![feature(try_as_dyn)]
use std::any::try_as_dyn;
trait Trait {}
fn store(_: &'static Box<i32>) {}
fn main() {
    let fn_ptr: fn(&'static Box<i32>) = store;
    let dt = try_as_dyn::<_, dyn Trait>(&fn_ptr);
}

Version information

rustc 1.97.0-nightly (8da2d28cb 2026-04-18)
binary: rustc
commit-hash: 8da2d28cbd5a4e2b93e028e709afe09541671663
commit-date: 2026-04-18
host: x86_64-unknown-linux-gnu
release: 1.97.0-nightly
LLVM version: 22.1.2

Possibly related line of code:
https://github.com/rust-lang/rust/blob/8da2d28cbd5a4e2b93e028e709afe09541671663/compiler/rustc_const_eval/src/util/check_validity_requirement.rs#L195-L207

Command:
/home/matthias/.rustup/toolchains/master/bin/rustc -Zmir-opt-level=5 -Zdump-mir=all -Zalways-encode-mir -Zextra-const-ub-checks

Program output 

warning: unused variable: `dt`
 --> /tmp/icemaker_global_tempdir.40wD6iU9umEx/rustc_testrunner_tmpdir_reporting.sfKgUu6cXCHu/mvce.rs:7:9
  |
7 |     let dt = try_as_dyn::<_, dyn Trait>(&fn_ptr);
  |         ^^ help: if this is intentional, prefix it with an underscore: `_dt`
  |
  = note: `#[warn(unused_variables)]` (part of `#[warn(unused)]`) on by default


thread 'rustc' (2380251) panicked at /rustc-dev/8da2d28cbd5a4e2b93e028e709afe09541671663/compiler/rustc_const_eval/src/util/check_validity_requirement.rs:201:41:
called `Result::unwrap()` on an `Err` value: InterpErrorInfo(InterpErrorInfoInner { kind: UndefinedBehavior(ValidationError { orig_ty: pattern_type!(*const Foreign(DefId(2:2767 ~ core[e86e]::ptr::metadata::{extern#0}::VTable)) is !null), path: None, msg: "encountered 0, but expected something greater or equal to 1", ptr_bytes_warning: false }), backtrace: InterpErrorBacktrace { backtrace: None } })
stack backtrace:
   0:     0x7f95b0a22ceb - <<std[d6a62db279dbae46]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[e86e8f32962a9819]::fmt::Display>::fmt
   1:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
   2:     0x7f95b0a39ce6 - <std[d6a62db279dbae46]::sys::stdio::unix::Stderr as std[d6a62db279dbae46]::io::Write>::write_fmt
   3:     0x7f95b09f8f68 - std[d6a62db279dbae46]::panicking::default_hook::{closure#0}
   4:     0x7f95b0a16353 - std[d6a62db279dbae46]::panicking::default_hook
   5:     0x7f95af9db02c - std[d6a62db279dbae46]::panicking::update_hook::<alloc[26814c36517be32d]::boxed::Box<rustc_driver_impl[945e7c8a3fc176fa]::install_ice_hook::{closure#1}>>::{closure#0}
   6:     0x7f95b0a16632 - std[d6a62db279dbae46]::panicking::panic_with_hook
   7:     0x7f95b09f9028 - std[d6a62db279dbae46]::panicking::panic_handler::{closure#0}
   8:     0x7f95b09efd69 - std[d6a62db279dbae46]::sys::backtrace::__rust_end_short_backtrace::<std[d6a62db279dbae46]::panicking::panic_handler::{closure#0}, !>
   9:     0x7f95b09faa8d - __rustc[3f76c9a779ba9221]::rust_begin_unwind
  10:     0x7f95ad58aa3c - core[e86e8f32962a9819]::panicking::panic_fmt
  11:     0x7f95ad104572 - core[e86e8f32962a9819]::result::unwrap_failed
  12:     0x7f95af959661 - rustc_const_eval[2f0023f731c85369]::util::check_validity_requirement::validate_scalar_in_layout
  13:     0x7f95afe6c906 - <rustc_const_eval[2f0023f731c85369]::provide::{closure#3} as core[e86e8f32962a9819]::ops::function::FnOnce<(rustc_middle[253f0d05195ba05e]::ty::context::TyCtxt, rustc_middle[253f0d05195ba05e]::ty::consts::int::ScalarInt, rustc_middle[253f0d05195ba05e]::ty::Ty)>>::call_once
  14:     0x7f95b00a9fa3 - <rustc_middle[253f0d05195ba05e]::ty::print::pretty::FmtPrinter as rustc_middle[253f0d05195ba05e]::ty::print::pretty::PrettyPrinter>::pretty_print_const_scalar_int
  15:     0x7f95b24aeda6 - rustc_middle[253f0d05195ba05e]::mir::pretty::pretty_print_const_value_tcx
  16:     0x7f95b24af58d - rustc_middle[253f0d05195ba05e]::mir::pretty::pretty_print_const_value_tcx
  17:     0x7f95b24af58d - rustc_middle[253f0d05195ba05e]::mir::pretty::pretty_print_const_value_tcx
  18:     0x7f95b24ae81a - <rustc_middle[253f0d05195ba05e]::mir::consts::Const as core[e86e8f32962a9819]::fmt::Display>::fmt
  19:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
  20:     0x7f95b00688f7 - <&alloc[26814c36517be32d]::boxed::Box<rustc_middle[253f0d05195ba05e]::mir::syntax::ConstOperand> as core[e86e8f32962a9819]::fmt::Debug>::fmt
  21:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
  22:     0x7f95b009663e - <rustc_middle[253f0d05195ba05e]::mir::syntax::Operand as core[e86e8f32962a9819]::fmt::Debug>::fmt
  23:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
  24:     0x7f95b00931ca - <rustc_middle[253f0d05195ba05e]::mir::syntax::Rvalue as core[e86e8f32962a9819]::fmt::Debug>::fmt
  25:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
  26:     0x7f95b007cf8d - <rustc_middle[253f0d05195ba05e]::mir::syntax::StatementKind as core[e86e8f32962a9819]::fmt::Debug>::fmt
  27:     0x7f95b102e808 - core[e86e8f32962a9819]::fmt::write
  28:     0x7f95b102e6d5 - alloc[26814c36517be32d]::fmt::format::format_inner
  29:     0x7f95b0027490 - <rustc_middle[253f0d05195ba05e]::mir::pretty::MirWriter>::write_mir_fn
  30:     0x7f95b0033319 - <rustc_middle[253f0d05195ba05e]::mir::pretty::MirDumper>::dump_mir_to_writer
  31:     0x7f95b0033473 - <rustc_middle[253f0d05195ba05e]::mir::pretty::MirDumper>::dump_mir
  32:     0x7f95b1009fe0 - rustc_mir_transform[5e6f23ecb9c29fca]::run_optimization_passes
  33:     0x7f95b147c5d4 - rustc_mir_transform[5e6f23ecb9c29fca]::optimized_mir
  34:     0x7f95b147c221 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::optimized_mir::invoke_provider_fn::__rust_begin_short_backtrace
  35:     0x7f95b10143cd - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::DefIdCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 8usize]>>, false>
  36:     0x7f95b1013a0e - rustc_query_impl[a6166eb9fe0387cf]::query_impl::optimized_mir::execute_query_non_incr::__rust_end_short_backtrace
  37:     0x7f95b1b0f58e - <rustc_middle[253f0d05195ba05e]::ty::context::TyCtxt>::instance_mir
  38:     0x7f95b1b13e0b - rustc_monomorphize[29aaa413ab07d6fb]::collector::items_of_instance
  39:     0x7f95b1b13d95 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::items_of_instance::invoke_provider_fn::__rust_begin_short_backtrace
  40:     0x7f95b1b108ae - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::DefaultCache<(rustc_middle[253f0d05195ba05e]::ty::instance::Instance, rustc_middle[253f0d05195ba05e]::mono::CollectionMode), rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 32usize]>>, false>
  41:     0x7f95b1b10511 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::items_of_instance::execute_query_non_incr::__rust_end_short_backtrace
  42:     0x7f95b24947b2 - rustc_monomorphize[29aaa413ab07d6fb]::collector::collect_items_rec
  43:     0x7f95b15fa761 - rustc_monomorphize[29aaa413ab07d6fb]::collector::collect_crate_mono_items::{closure#1}::{closure#0}
  44:     0x7f95b16f3759 - rustc_monomorphize[29aaa413ab07d6fb]::partitioning::collect_and_partition_mono_items
  45:     0x7f95b16f33f0 - rustc_query_impl[a6166eb9fe0387cf]::query_impl::collect_and_partition_mono_items::invoke_provider_fn::__rust_begin_short_backtrace
  46:     0x7f95b21b8834 - rustc_query_impl[a6166eb9fe0387cf]::execution::try_execute_query::<rustc_middle[253f0d05195ba05e]::query::caches::SingleCache<rustc_middle[253f0d05195ba05e]::query::erase::ErasedData<[u8; 24usize]>>, false>
  47:     0x7f95b21b85ca - rustc_query_impl[a6166eb9fe0387cf]::query_impl::collect_and_partition_mono_items::execute_query_non_incr::__rust_end_short_backtrace
  48:     0x7f95b22a6679 - rustc_codegen_ssa[c4865c8fd6c4e2a4]::base::codegen_crate::<rustc_codegen_llvm[a5f9bd01c842ba63]::LlvmCodegenBackend>
  49:     0x7f95b22a63a5 - <rustc_codegen_llvm[a5f9bd01c842ba63]::LlvmCodegenBackend as rustc_codegen_ssa[c4865c8fd6c4e2a4]::traits::backend::CodegenBackend>::codegen_crate
  50:     0x7f95b21996b2 - <rustc_interface[1d873664835f04c7]::queries::Linker>::codegen_and_build_linker
  51:     0x7f95b2193926 - rustc_interface[1d873664835f04c7]::interface::run_compiler::<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}
  52:     0x7f95b216b28a - std[d6a62db279dbae46]::sys::backtrace::__rust_begin_short_backtrace::<rustc_interface[1d873664835f04c7]::util::run_in_thread_with_globals<rustc_interface[1d873664835f04c7]::util::run_in_thread_pool_with_globals<rustc_interface[1d873664835f04c7]::interface::run_compiler<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>
  53:     0x7f95b216b96d - <std[d6a62db279dbae46]::thread::lifecycle::spawn_unchecked<rustc_interface[1d873664835f04c7]::util::run_in_thread_with_globals<rustc_interface[1d873664835f04c7]::util::run_in_thread_pool_with_globals<rustc_interface[1d873664835f04c7]::interface::run_compiler<(), rustc_driver_impl[945e7c8a3fc176fa]::run_compiler::{closure#0}>::{closure#1}, ()>::{closure#0}, ()>::{closure#0}::{closure#0}, ()>::{closure#1} as core[e86e8f32962a9819]::ops::function::FnOnce<()>>::call_once::{shim:vtable#0}
  54:     0x7f95b216c7ec - <std[d6a62db279dbae46]::sys::thread::unix::Thread>::new::thread_start
  55:     0x7f95abca597a - <unknown>
  56:     0x7f95abd292bc - <unknown>
  57:                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 1.97.0-nightly (8da2d28cb 2026-04-18) running on x86_64-unknown-linux-gnu

note: compiler flags: -Z mir-opt-level=5 -Z dump-mir=all -Z always-encode-mir -Z extra-const-ub-checks -Z dump-mir-dir=dir

query stack during panic:
#0 [optimized_mir] optimizing MIR for `main`
#1 [items_of_instance] collecting items used by `main`
#2 [collect_and_partition_mono_items] collect_and_partition_mono_items
end of query stack
warning: 1 warning emitted

@rustbot label +F-try_as_dyn

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Research direction

Reproduce the ICE with the supplied main.rs snippet and compiler flags, then start at compiler/rustc_const_eval/src/util/check_validity_requirement.rs:195-207. Trace why validation of the vtable pointer reaches the unwrap during MIR dumping; done means the reproducer no longer panics under these flags, with a regression test covering it.

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
45/100

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