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Uninhabited repr(uX) enum shouldn't have size zero #146984
Description
I tried this code:
#[derive(Clone, Copy)]
enum Never {}
#[repr(u32)]
enum MyEnum {
A(Never),
B(Never),
}
#[repr(C)]
union MyEnumRepr {
A: MyVariantA,
B: MyVariantB,
}
#[repr(u32)]
#[derive(Copy, Clone)]
enum MyEnumDiscriminant { A, B }
#[repr(C)]
#[derive(Clone, Copy)]
struct MyVariantA(MyEnumDiscriminant, Never);
#[repr(C)]
#[derive(Clone, Copy)]
struct MyVariantB(MyEnumDiscriminant, Never);
fn main() {
println!("{}", size_of::<MyEnum>());
println!("{}", size_of::<MyEnumRepr>());
}I expected MyEnum and MyEnumRepr to have the same size, since this is the desugaring given as an example in the reference.
Instead, MyEnum has size 0, while MyEnumRepr has size 4.
Discovered by masterjason9637 on the rust community discord.
Meta
Reproducible on the playground with version 1.92.0-nightly (2025-09-23 975e6c8fec280816d24f)
Activity
[-]Uninhibited `repr(uX)` enum shouldn't have size zero[/-][+]Uninhabited `repr(uX)` enum shouldn't have size zero[/+]zachs18 commentedon Sep 24, 2025
@rustbot claim
Rollup merge of rust-lang#146989 - zachs18:fix-146984, r=SparrowLii
Unrolled build for #146989
Rollup merge of #146989 - zachs18:fix-146984, r=SparrowLii
Rollup merge of #146989 - zachs18:fix-146984, r=SparrowLii
Rollup merge of #146989 - zachs18:fix-146984, r=SparrowLii