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#![crate_type = "lib"]
#![feature(transmutability)]
#![allow(dead_code, incomplete_features, non_camel_case_types)]
mod assert {
use std::mem::{Assume, TransmuteFrom};
pub fn is_maybe_transmutable<Src, Dst>()
where
Dst: TransmuteFrom<Src, {
Assume {
alignment: true,
lifetimes: true,
safety: true,
validity: true,
}
}>
{}
}
fn void() {
enum Void {}
// This transmutation is vacuously acceptable; since one cannot construct a
// `Void`, unsoundness cannot directly arise from transmuting a void into
// anything else.
assert::is_maybe_transmutable::<Void, u128>();
assert::is_maybe_transmutable::<(), Void>(); //~ ERROR: cannot be safely transmuted
}
// Non-ZST uninhabited types are, nonetheless, uninhabited.
fn yawning_void_struct() {
enum Void {}
struct YawningVoid(Void, u128);
const _: () = {
assert!(std::mem::size_of::<YawningVoid>() == std::mem::size_of::<u128>());
// Just to be sure the above constant actually evaluated:
assert!(false); //~ ERROR: evaluation of constant value failed
};
// This transmutation is vacuously acceptable; since one cannot construct a
// `Void`, unsoundness cannot directly arise from transmuting a void into
// anything else.
assert::is_maybe_transmutable::<YawningVoid, u128>();
assert::is_maybe_transmutable::<(), Void>(); //~ ERROR: cannot be safely transmuted
}
// Non-ZST uninhabited types are, nonetheless, uninhabited.
fn yawning_void_enum() {
enum Void {}
enum YawningVoid {
A(Void, u128),
}
const _: () = {
assert!(std::mem::size_of::<YawningVoid>() == std::mem::size_of::<u128>());
// Just to be sure the above constant actually evaluated:
assert!(false); //~ ERROR: evaluation of constant value failed
};
// This transmutation is vacuously acceptable; since one cannot construct a
// `Void`, unsoundness cannot directly arise from transmuting a void into
// anything else.
assert::is_maybe_transmutable::<YawningVoid, u128>();
assert::is_maybe_transmutable::<(), Void>(); //~ ERROR: cannot be safely transmuted
}
// References to uninhabited types are, logically, uninhabited, but for layout
// purposes are not ZSTs, and aren't treated as uninhabited when they appear in
// enum variants.
fn distant_void() {
enum Void {}
enum DistantVoid {
A(&'static Void)
}
const _: () = {
assert!(std::mem::size_of::<DistantVoid>() == std::mem::size_of::<usize>());
// Just to be sure the above constant actually evaluated:
assert!(false); //~ ERROR: evaluation of constant value failed
};
assert::is_maybe_transmutable::<DistantVoid, ()>();
assert::is_maybe_transmutable::<DistantVoid, &'static Void>();
assert::is_maybe_transmutable::<u128, DistantVoid>(); //~ ERROR: cannot be safely transmuted
}
fn issue_126267() {
pub enum ApiError {}
pub struct TokioError {
b: bool,
}
pub enum Error {
Api { source: ApiError }, // this variant is uninhabited
Ethereum,
Tokio { source: TokioError },
}
struct Src;
type Dst = Error;
assert::is_maybe_transmutable::<Src, Dst>(); //~ERROR: cannot be safely transmuted
}
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