rust/tests/ui/union/union-deref.rs

// revisions: mirunsafeck thirunsafeck
// [thirunsafeck]compile-flags: -Z thir-unsafeck

//! Test the part of RFC 2514 that is about not applying `DerefMut` coercions
//! of union fields.

use std::mem::ManuallyDrop;

union U1<T> { x:(), f: ManuallyDrop<(T,)> }

union U2<T> { x:(), f: (ManuallyDrop<(T,)>,) }

fn main() {
    let mut u : U1<Vec<i32>> = U1 { x: () };
    unsafe { (*u.f).0 = Vec::new() }; // explicit deref, this compiles
    unsafe { u.f.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
    unsafe { &mut (*u.f).0 }; // explicit deref, this compiles
    unsafe { &mut u.f.0 }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
    unsafe { (*u.f).0.push(0) }; // explicit deref, this compiles
    unsafe { u.f.0.push(0) }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field

    let mut u : U2<Vec<i32>> = U2 { x: () };
    unsafe { (*u.f.0).0 = Vec::new() }; // explicit deref, this compiles
    unsafe { u.f.0.0 = Vec::new() }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
    unsafe { &mut (*u.f.0).0 }; // explicit deref, this compiles
    unsafe { &mut u.f.0.0 }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
    unsafe { (*u.f.0).0.push(0) }; // explicit deref, this compiles
    unsafe { u.f.0.0.push(0) }; //~ERROR not automatically applying `DerefMut` on `ManuallyDrop` union field
}