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interpret: project_downcast: do not ICE for uninhabited variants

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Ralf Jung 2024-01-26 08:22:05 +01:00
parent 69db514ed9
commit 1025a12b64
4 changed files with 30 additions and 19 deletions
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21
compiler/rustc_const_eval/src/interpret/projection.rs
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@ -201,25 +201,8 @@ where
// see https://github.com/rust-lang/rust/issues/93688#issuecomment-1032929496.)
// So we just "offset" by 0.
let layout = base.layout().for_variant(self, variant);
// In the future we might want to allow this to permit code like this:
// (this is a Rust/MIR pseudocode mix)
// ```
// enum Option2 {
// Some(i32, !),
// None,
// }
//
// fn panic() -> ! { panic!() }
//
// let x: Option2;
// x.Some.0 = 42;
// x.Some.1 = panic();
// SetDiscriminant(x, Some);
// ```
// However, for now we don't generate such MIR, and this check here *has* found real
// bugs (see https://github.com/rust-lang/rust/issues/115145), so we will keep rejecting
// it.
assert!(!layout.abi.is_uninhabited());
// This variant may in fact be uninhabited.
// See <https://github.com/rust-lang/rust/issues/120337>.
// This cannot be `transmute` as variants *can* have a smaller size than the entire enum.
base.offset(Size::ZERO, layout, self)