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

[cushionbadak]

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)

//@ 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<Error> 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<E> {
    /// 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<Src, Dst>()
    where
        Dst: BikeshedIntrinsicFrom<Src> // safety is NOT assumed
    {}
}

fn test() {
    #[repr(C)]
    struct Src;
    type Dst = Error;
    assert::is_transmutable::<Src, Dst>();
}

Meta

rustc --version --verbose:

rustc 1.81.0-nightly (b5b13568f 2024-06-10)
binary: rustc
commit-hash: b5b13568fb5da4ac988bde370008d6134d3dfe6c
commit-date: 2024-06-10
host: x86_64-apple-darwin
release: 1.81.0-nightly
LLVM version: 18.1.7

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: <rustc_transmute::layout::tree::Tree<rustc_transmute::layout::rustc::Def, rustc_transmute::layout::rustc::Ref>>::from_enum
   5: <rustc_transmute::rustc::TransmuteTypeEnv>::is_transmutable
   6: <rustc_trait_selection::traits::select::SelectionContext>::confirm_candidate
   7: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_candidate::{closure#0}::{closure#0}
   8: <rustc_infer::infer::InferCtxt>::probe::<core::result::Result<rustc_middle::traits::select::EvaluationResult, rustc_middle::traits::select::OverflowError>, <rustc_trait_selection::traits::select::SelectionContext>::evaluation_probe<<rustc_trait_selection::traits::select::SelectionContext>::evaluate_candidate::{closure#0}::{closure#0}>::{closure#0}>
   9: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_trait_predicate_recursively::{closure#0}::{closure#1}
  10: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_trait_predicate_recursively::{closure#0}
  11: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_predicate_recursively::{closure#0}::{closure#0}
  12: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_root_obligation::{closure#0}
  13: <rustc_trait_selection::traits::select::SelectionContext>::evaluate_root_obligation
  14: rustc_traits::evaluate_obligation::evaluate_obligation
      [... omitted 2 frames ...]
  15: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation
  16: <rustc_infer::infer::InferCtxt as rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt>::evaluate_obligation_no_overflow
  17: <rustc_trait_selection::traits::fulfill::FulfillProcessor>::process_trait_obligation
  18: <rustc_trait_selection::traits::fulfill::FulfillProcessor as rustc_data_structures::obligation_forest::ObligationProcessor>::process_obligation
  19: <rustc_data_structures::obligation_forest::ObligationForest<rustc_trait_selection::traits::fulfill::PendingPredicateObligation>>::process_obligations::<rustc_trait_selection::traits::fulfill::FulfillProcessor>
  20: <rustc_trait_selection::traits::fulfill::FulfillmentContext<rustc_trait_selection::traits::FulfillmentError> as rustc_infer::traits::engine::TraitEngine<rustc_trait_selection::traits::FulfillmentError>>::select_where_possible
  21: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_argument_types
  22: <rustc_hir_typeck::fn_ctxt::FnCtxt>::confirm_builtin_call
  23: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_kind
  24: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  25: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_block_with_expected
  26: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_expr_with_expectation_and_args
  27: <rustc_hir_typeck::fn_ctxt::FnCtxt>::check_return_expr
  28: rustc_hir_typeck::check::check_fn
  29: rustc_hir_typeck::typeck
      [... omitted 1 frame ...]
  30: <rustc_middle::hir::map::Map>::par_body_owners::<rustc_hir_analysis::check_crate::{closure#4}>::{closure#0}
  31: rustc_hir_analysis::check_crate
  32: rustc_interface::passes::run_required_analyses
  33: rustc_interface::passes::analysis
      [... omitted 1 frame ...]
  34: <rustc_interface::queries::QueryResult<&rustc_middle::ty::context::GlobalCtxt>>::enter::<core::result::Result<(), rustc_span::ErrorGuaranteed>, rustc_driver_impl::run_compiler::{closure#0}::{closure#1}::{closure#3}>
  35: rustc_interface::interface::run_compiler::<core::result::Result<(), rustc_span::ErrorGuaranteed>, 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<test::Src, core::mem::transmutability::Assume { alignment: false, lifetimes: false, safety: false, validity: false }>`
#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
  

  rust/compiler/rustc_const_eval/src/interpret/discriminant.rs

  Lines 276 to 288 in b5b1356

  	abi::Variants::Multiple {
  	tag_encoding:
  	TagEncoding::Niche { untagged_variant, ref niche_variants, niche_start },
  	tag: tag_layout,
  	tag_field,
  	..
  	} => {
  	assert!(variant_index != untagged_variant);
  	let variants_start = niche_variants.start().as_u32();
  	let variant_index_relative = variant_index
  	.as_u32()
  	.checked_sub(variants_start)
  	.expect("overflow computing relative variant idx");

• If constructor Ethereum or Tokio removed from enum definition in the reduced ICE triggering code (Line 10, 11), ICE: compiler/rustc_const_eval/src/interpret/discriminant.rs assertion failed 0 != 1  #125811 will be triggered.
  • (compiler/rustc_const_eval/src/interpret/discriminant.rs L245)
    

    rust/compiler/rustc_const_eval/src/interpret/discriminant.rs

    Lines 243 to 247 in b5b1356

    	match self.layout_of(ty)?.variants {
    	abi::Variants::Single { index } => {
    	assert_eq!(index, variant_index);
    	Ok(None)
    	}

• Closed issue-66787 might be related.

@rustbot label +F-transmutability

[cushionbadak]

Regression in rust-lang-ci@d48eec5
The PR introducing the regression in this rollup is #123367: Safe Transmute: Compute transmutability from `rustc_target:…

searched nightlies: from nightly-2023-01-01 to nightly-2024-05-30
regressed nightly: nightly-2024-04-09
searched commit range: 9d5cdf7...ab5bda1
regressed commit: ab5bda1

bisected with cargo-bisect-rustc v0.6.8

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc --start=2023-01-01 --end=2024-05-30 --regress=ice --script=rustc --preserve -- 126267.rs