ICE: `overflow computing relative variant idx` in `rustc_const_eval/src/interpret/discriminant.rs`

Code

(hand-reduced)

#![feature(transmutability)]
#![crate_type = "lib"]

pub enum ApiError {}
pub struct TokioError {
    b: bool,
}
pub enum Error {
    Api { source: ApiError },
    Ethereum,
    Tokio { source: TokioError },
}

mod assert {
    use std::mem::BikeshedIntrinsicFrom;

    pub fn is_transmutable<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src>, // safety is NOT assumed
    {
    }
}

fn test() {
    struct Src;
    type Dst = Error;
    assert::is_transmutable::<Src, Dst>();
}

(original)

```Rust //@ compile-flags: -C opt-level=0 #![crate_type = "lib"] pub enum ApiError {} #[allow(dead_code)] pub struct TokioError { b: bool, } pub enum Error { Api { source: ApiError }, Ethereum, Tokio { source: TokioError }, } struct Api; impl IntoError for Api { type Source = ApiError; // CHECK-LABEL: @into_error // CHECK: llvm.trap() // Also check the next two instructions to make sure we do not match against `trap` // elsewhere in the code. // CHECK-NEXT: load // CHECK-NEXT: ret #[no_mangle] fn into_error(self, error: Self::) -> Error { Error::Api { source: error } } } pub trait IntoError { /// The underlying error type Source; /// Combine the information to produce the error fn into_error(self, source: Self::Source) -> E; } //@ check-pass //! The presence of safety invariants in the source type does not affect //! transmutability. #![crate_type = "lib"] #![feature(transmutability)] #![allow(dead_code)] mod assert { use std::mem::BikeshedIntrinsicFrom; pub fn is_transmutable() where Dst: BikeshedIntrinsicFrom // safety is NOT assumed {} } fn test() { #[repr(C)] struct Src; type Dst = Error; assert::is_transmutable::(); } ```

Error output

Command: rustc

<output>

Backtrace

``` thread 'rustc' panicked at compiler/rustc_const_eval/src/interpret/discriminant.rs:288:22: overflow computing relative variant idx stack backtrace: 0: _rust_begin_unwind 1: core::panicking::panic_fmt 2: core::option::expect_failed 3: rustc_const_eval::const_eval::tag_for_variant_provider [... omitted 2 frames ...] 4: >::from_enum 5: ::is_transmutable 6: ::confirm_candidate 7: ::evaluate_candidate::{closure#0}::{closure#0} 8: ::probe::, ::evaluation_probe<::evaluate_candidate::{closure#0}::{closure#0}>::{closure#0}> 9: ::evaluate_trait_predicate_recursively::{closure#0}::{closure#1} 10: ::evaluate_trait_predicate_recursively::{closure#0} 11: ::evaluate_predicate_recursively::{closure#0}::{closure#0} 12: ::evaluate_root_obligation::{closure#0} 13: ::evaluate_root_obligation 14: rustc_traits::evaluate_obligation::evaluate_obligation [... omitted 2 frames ...] 15: ::evaluate_obligation 16: ::evaluate_obligation_no_overflow 17: ::process_trait_obligation 18: ::process_obligation 19: >::process_obligations:: 20: as rustc_infer::traits::engine::TraitEngine>::select_where_possible 21: ::check_argument_types 22: ::confirm_builtin_call 23: ::check_expr_kind 24: ::check_expr_with_expectation_and_args 25: ::check_block_with_expected 26: ::check_expr_with_expectation_and_args 27: ::check_return_expr 28: rustc_hir_typeck::check::check_fn 29: rustc_hir_typeck::typeck [... omitted 1 frame ...] 30: ::par_body_owners::::{closure#0} 31: rustc_hir_analysis::check_crate 32: rustc_interface::passes::run_required_analyses 33: rustc_interface::passes::analysis [... omitted 1 frame ...] 34: >::enter::, rustc_driver_impl::run_compiler::{closure#0}::{closure#1}::{closure#3}> 35: 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. 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: please attach the file at `/Volumes/T7/workspace/240607_100chaos_tree_combine_typ/icefiles/rustc-ice-2024-06-11T10_43_12-38775.txt` to your bug report query stack during panic: #0 [tag_for_variant] computing variant tag for enum #1 [evaluate_obligation] evaluating trait selection obligation `Error: core::mem::transmutability::BikeshedIntrinsicFrom` #2 [typeck] type-checking `test` #3 [analysis] running analysis passes on this crate end of query stack ```

Notes

ICE location: compiler/rustc_const_eval/src/interpret/discriminant.rs L288 https://github.com/rust-lang/rust/blob/b5b13568fb5da4ac988bde370008d6134d3dfe6c/compiler/rustc_const_eval/src/interpret/discriminant.rs#L276-L288
If constructor Ethereum or Tokio removed from enum definition in the reduced ICE triggering code (Line 10, 11), #125811 will be triggered.
- (compiler/rustc_const_eval/src/interpret/discriminant.rs L245) https://github.com/rust-lang/rust/blob/b5b13568fb5da4ac988bde370008d6134d3dfe6c/compiler/rustc_const_eval/src/interpret/discriminant.rs#L243-L247
Closed issue-66787 might be related.

@rustbot label +F-transmutability

rust-lang / rust