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#![warn(rust_2018_idioms, single_use_lifetimes)]
// unaligned_references did not exist in older compilers and safe_packed_borrows was removed in the latest compilers.
#![allow(unknown_lints, renamed_and_removed_lints)]
#![forbid(unaligned_references, safe_packed_borrows)]
use std::cell::Cell;
// Ensure that the compiler doesn't copy the fields
// of #[repr(packed)] types during drop, if the field has alignment 1
// (that is, any reference to the field is guaranteed to have proper alignment)
// We are currently unable to statically prevent the usage of #[pin_project]
// on #[repr(packed)] types composed entirely of fields of alignment 1.
// This shouldn't lead to undefined behavior, as long as the compiler doesn't
// try to move the field anyway during drop.
//
// This tests validates that the compiler is doing what we expect.
#[test]
fn weird_repr_packed() {
// We keep track of the field address during
// drop using a thread local, to avoid changing
// the layout of our #[repr(packed)] type.
thread_local! {
static FIELD_ADDR: Cell<usize> = Cell::new(0);
}
#[repr(packed)]
struct Struct {
field: u8,
}
impl Drop for Struct {
fn drop(&mut self) {
FIELD_ADDR.with(|f| {
f.set(&self.field as *const u8 as usize);
});
}
}
#[allow(clippy::let_and_return)]
let field_addr = {
// We let this field drop by going out of scope,
// rather than explicitly calling drop(foo).
// Calling drop(foo) causes 'foo' to be moved
// into the 'drop' function, resulting in a different
// address.
let x = Struct { field: 27 };
let field_addr = &x.field as *const u8 as usize;
field_addr
};
assert_eq!(field_addr, FIELD_ADDR.with(Cell::get));
}