IntoBytes derives fails with (even unused) generics + packed(n > 1) #2533
Description
Here is an MRE for my problem:
use zerocopy::{Immutable, IntoBytes};
#[repr(C, packed(4))]
#[derive(Debug, Clone, Copy, Immutable, IntoBytes)]
pub struct Header {
pub a: u32,
pub b: u32,
}
const _: () = assert!(std::mem::size_of::<Header>() == 8);
#[repr(C, packed(4))]
#[derive(Debug, Clone, Copy, Immutable, IntoBytes)]
pub struct Data {
pub a: i64,
pub b: u8,
pub c: u8,
pub d: u16,
pub e: f32,
pub f: u16,
pub g: u16,
pub h: [u16; 4],
pub i: u16,
pub _padding: u16,
}
const _: () = assert!(std::mem::size_of::<Data>() == 32);
#[repr(C, packed(4))]
#[derive(Debug, Clone, Copy, Immutable, IntoBytes)]
pub struct Packet<const S: usize> {
pub header: Header,
pub data: Data,
//moredata: [u16; S], // Flexible array member
}
//const _: () = assert!(std::mem::size_of::<Packet<0>>() == 40);The error:
error[E0277]: the trait bound `Data: zerocopy::Unaligned` is not satisfied
--> src/lib.rs:28:41
|
28 | #[derive(Debug, Clone, Copy, Immutable, IntoBytes)]
| ^^^^^^^^^ the trait `zerocopy::Unaligned` is not implemented for `Data`
|
= note: Consider adding `#[derive(Unaligned)]` to `Data`
= help: the following other types implement trait `zerocopy::Unaligned`:
()
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
and 25 others
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
error[E0277]: the trait bound `Header: zerocopy::Unaligned` is not satisfied
--> src/lib.rs:28:41
|
28 | #[derive(Debug, Clone, Copy, Immutable, IntoBytes)]
| ^^^^^^^^^ the trait `zerocopy::Unaligned` is not implemented for `Header`
|
= note: Consider adding `#[derive(Unaligned)]` to `Header`
= help: the following other types implement trait `zerocopy::Unaligned`:
()
AtomicBool
AtomicI8
AtomicU8
Cell<T>
F32<O>
F64<O>
I128<O>
and 25 others
= help: see issue #48214
= note: this error originates in the derive macro `IntoBytes` (in Nightly builds, run with -Z macro-backtrace for more info)
For more information about this error, try `rustc --explain E0277`.
error: could not compile `playground` (lib) due to 2 previous errors
If I remove the generic parameter on Packet entirely, the code compiles, although it is unused in the actual layout (the FAM is commented out).
Replacing packed(4) with packed works (even with the generic).