1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
|
//@ check-pass
//! Adapted from https://rust-lang.github.io/unsafe-code-guidelines/layout/enums.html#explicit-repr-annotation-without-c-compatibility
#![crate_type = "lib"]
#![feature(transmutability)]
#![allow(dead_code, incomplete_features, non_camel_case_types)]
use std::mem::MaybeUninit;
mod assert {
use std::mem::{Assume, TransmuteFrom};
pub fn is_transmutable<Src, Dst>()
where
Dst: TransmuteFrom<Src, {
Assume {
alignment: false,
lifetimes: false,
safety: true,
validity: false,
}
}>
{}
pub fn is_maybe_transmutable<Src, Dst>()
where
Dst: TransmuteFrom<Src, {
Assume {
alignment: false,
lifetimes: false,
safety: true,
validity: true,
}
}>
{}
}
#[repr(u8)] enum V0 { V = 0 }
#[repr(u8)] enum V1 { V = 1 }
fn repr_u8() {
#[repr(u8)]
enum TwoCases {
A(u8, u16), // 0x00 INIT INIT INIT
B(u16), // 0x01 PADD INIT INIT
}
const _: () = {
assert!(std::mem::size_of::<TwoCases>() == 4);
};
#[repr(C)] struct TwoCasesA(V0, u8, u8, u8);
#[repr(C)] struct TwoCasesB(V1, MaybeUninit<u8>, u8, u8);
assert::is_transmutable::<TwoCasesA, TwoCases>();
assert::is_transmutable::<TwoCasesB, TwoCases>();
assert::is_maybe_transmutable::<TwoCases, TwoCasesA>();
assert::is_maybe_transmutable::<TwoCases, TwoCasesB>();
}
fn repr_c_u8() {
#[repr(C, u8)]
enum TwoCases {
A(u8, u16), // 0x00 PADD INIT PADD INIT INIT
B(u16), // 0x01 PADD INIT INIT PADD PADD
}
const _: () = {
assert!(std::mem::size_of::<TwoCases>() == 6);
};
#[repr(C)] struct TwoCasesA(V0, MaybeUninit<u8>, u8, MaybeUninit<u8>, u8, u8);
#[repr(C)] struct TwoCasesB(V1, MaybeUninit<u8>, u8, u8, MaybeUninit<u8>, MaybeUninit<u8>);
assert::is_transmutable::<TwoCasesA, TwoCases>();
assert::is_transmutable::<TwoCasesB, TwoCases>();
assert::is_maybe_transmutable::<TwoCases, TwoCasesA>();
assert::is_maybe_transmutable::<TwoCases, TwoCasesB>();
}
|
