panic: unreachable: const eval

pub mod empty {
    #[derive(Clone, Copy)]
    enum Void {}

    #[derive(Clone, Copy)]
    pub struct Empty(Void);
}

const BAR: [empty::Empty; 3] = [unsafe { std::mem::transmute(()) }; 3];

fn main() {
    BAR;
}

rust-analyzer analysis-stats . --run-all-ide-things

Database loaded:     579.84ms, 229minstr, 48mb (metadata 287.33ms, 1010kinstr, 151kb; build 33.08ms, 180kinstr, 2144b)
  item trees: 1
  dependency lines of code: 1_467_433, item trees: 2_948
  dependency item stats: traits: 848, impl: 9_686, mods: 3_059, macro calls: 5_580, macro rules: 1_054
Item Tree Collection: 4.30s, 23ginstr, 427mb
  Total Statistics:
    crates: 1, mods: 2, decls: 7, bodies: 4, adts: 2, consts: 1, signatures: 10, variants: 1
  Workspace:
    traits: 0, macro_rules macros: 0, proc_macros: 0
    lines of code: 13, item trees: 1
    usages: traits: 0, impl: 0, mods: 1, macro calls: 0, macro rules: 0
  Dependencies:
    lines of code: 1_467_433, item trees: 2_948
    declarations: traits: 848, impl: 9_686, mods: 3_059, macro calls: 5_580, macro rules: 1_054
Item Collection:     2.56s, 11ginstr, 179mb
Crate lang items:    438.20ms, 2474minstr, 31mb
Expression Store Lowering: 263.13µs, 402kinstr, 7kb
  exprs: 8, ??ty: 0 (0%), ?ty: 0 (0%), !ty: 0
  pats: 0, ??ty: 0 (100%), ?ty: 0 (100%), !ty: 0
  panics: 0
Inference:           311.82ms, 1347minstr, 35mb
MIR lowering:        257.28µs, 395kinstr, 34kb
Mir failed bodies: 0 (0%)
Data layouts:        69.03µs, 59kinstr, 177kb
Failed data layouts: 0 (0%)
0/1 0% const eval: ra::BAR
thread 'main' (1775730) panicked at src/tools/rust-analyzer/crates/hir-ty/src/utils.rs:104:45:
internal error: entered unreachable code
stack backtrace:
   0:     0x7fa7d5ca6246 - <<std[74eb2aff46e51e81]::sys::backtrace::BacktraceLock>::print::DisplayBacktrace as core[7aff35c028b048a4]::fmt::Display>::fmt
   1:     0x7fa7d640ad52 - core[7aff35c028b048a4]::fmt::write
   2:     0x7fa7d5cbb38c - <std[74eb2aff46e51e81]::sys::stdio::unix::Stderr as core[7aff35c028b048a4]::io::write::Write>::write_fmt
   3:     0x7fa7d5c77e7a - std[74eb2aff46e51e81]::panicking::default_hook::{closure#0}
   4:     0x7fa7d5c988e3 - std[74eb2aff46e51e81]::panicking::default_hook
   5:     0x7fa7d5c98d4b - std[74eb2aff46e51e81]::panicking::panic_with_hook
   6:     0x7fa7d5c77f64 - std[74eb2aff46e51e81]::panicking::panic_handler::{closure#0}
   7:     0x7fa7d5c6f3e9 - std[74eb2aff46e51e81]::sys::backtrace::__rust_end_short_backtrace::<std[74eb2aff46e51e81]::panicking::panic_handler::{closure#0}, !>
   8:     0x7fa7d5c7988d - __rustc[49844a0cf2bb6b0d]::rust_begin_unwind
   9:     0x7fa7d2a33c7c - core[7aff35c028b048a4]::panicking::panic_fmt
  10:     0x7fa7d2df2952 - core[7aff35c028b048a4]::panicking::panic
  11:     0x562d57cbe765 - hir_ty[f58a0abe133f1c00]::utils::detect_variant_from_bytes
  12:     0x562d57cf05f2 - <hir_ty[f58a0abe133f1c00]::mir::eval::Evaluator>::create_memory_map::rec
  13:     0x562d57cf11e2 - <hir_ty[f58a0abe133f1c00]::mir::eval::Evaluator>::create_memory_map::rec
  14:     0x562d57cf0f1b - <hir_ty[f58a0abe133f1c00]::mir::eval::Evaluator>::create_memory_map::rec
  15:     0x562d57cdc47f - hir_ty[f58a0abe133f1c00]::mir::eval::interpret_mir
  16:     0x562d57d5dab8 - <hir_ty[f58a0abe133f1c00]::consteval::const_eval::_::const_eval_query_Configuration_ as salsa[8774cceebe7971b6]::function::Configuration>::execute
  17:     0x562d57b7d10b - <salsa[8774cceebe7971b6]::function::IngredientImpl<hir_ty[f58a0abe133f1c00]::consteval::const_eval::_::const_eval_query_Configuration_>>::execute
  18:     0x562d57ccd72c - hir_ty[f58a0abe133f1c00]::consteval::const_eval
  19:     0x562d5892bed6 - <rust_analyzer[f1820004a41e425c]::cli::flags::AnalysisStats>::run::{closure#3}
  20:     0x562d58987762 - <rust_analyzer[f1820004a41e425c]::cli::flags::AnalysisStats>::run
  21:     0x562d58bc6fd6 - rust_analyzer[c4fd19d1c3329aa5]::main
  22:     0x562d58bc3373 - std[74eb2aff46e51e81]::sys::backtrace::__rust_begin_short_backtrace::<fn() -> core[7aff35c028b048a4]::result::Result<std[74eb2aff46e51e81]::process::ExitCode, anyhow[f3ff20ce718c24c8]::Error>, core[7aff35c028b048a4]::result::Result<std[74eb2aff46e51e81]::process::ExitCode, anyhow[f3ff20ce718c24c8]::Error>>
  23:     0x562d58bc50d2 - std[74eb2aff46e51e81]::rt::lang_start::<core[7aff35c028b048a4]::result::Result<std[74eb2aff46e51e81]::process::ExitCode, anyhow[f3ff20ce718c24c8]::Error>>::{closure#0}
  24:     0x7fa7d7503553 - std[74eb2aff46e51e81]::rt::lang_start_internal
  25:     0x562d58bddb68 - main
  26:     0x7fa7d0a27741 - <unknown>
  27:     0x7fa7d0a27879 - __libc_start_main
  28:     0x562d574c1ed9 - <unknown>
  29:                0x0 - <unknown>

rust-analyzer 1.99.0-nightly (26ae60a 2026-07-28)

Reproduce the issue with rust-analyzer analysis-stats . --run-all-ide-things using the provided Rust snippet. Start at crates/hir-ty/src/utils.rs, especially detect_variant_from_bytes, and follow its call from Evaluator::create_memory_map. Done means the input no longer causes an internal panic during const evaluation.