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// rust-lang/rust#45696: This test is checking that we can return
// mutable borrows owned by boxes even when the boxes are dropped.
// run-pass
// This function shows quite directly what is going on: We have a
// reborrow of contents within the box.
fn return_borrow_from_dropped_box_1(x: Box<&mut u32>) -> &mut u32 { &mut **x }
// This function is the way you'll probably see this in practice (the
// reborrow is now implicit).
fn return_borrow_from_dropped_box_2(x: Box<&mut u32>) -> &mut u32 { *x }
// For the remaining tests we just add some fields or other
// indirection to ensure that the compiler isn't just special-casing
// the above `Box<&mut T>` as the only type that would work.
// Here we add a tuple of indirection between the box and the
// reference.
type BoxedTup<'a, 'b> = Box<(&'a mut u32, &'b mut u32)>;
fn return_borrow_of_field_from_dropped_box_1<'a>(x: BoxedTup<'a, '_>) -> &'a mut u32 {
&mut *x.0
}
fn return_borrow_of_field_from_dropped_box_2<'a>(x: BoxedTup<'a, '_>) -> &'a mut u32 {
x.0
}
fn return_borrow_from_dropped_tupled_box_1<'a>(x: (BoxedTup<'a, '_>, &mut u32)) -> &'a mut u32 {
&mut *(x.0).0
}
fn return_borrow_from_dropped_tupled_box_2<'a>(x: (BoxedTup<'a, '_>, &mut u32)) -> &'a mut u32 {
(x.0).0
}
fn basic_tests() {
let mut x = 2;
let mut y = 3;
let mut z = 4;
*return_borrow_from_dropped_box_1(Box::new(&mut x)) += 10;
assert_eq!((x, y, z), (12, 3, 4));
*return_borrow_from_dropped_box_2(Box::new(&mut x)) += 10;
assert_eq!((x, y, z), (22, 3, 4));
*return_borrow_of_field_from_dropped_box_1(Box::new((&mut x, &mut y))) += 10;
assert_eq!((x, y, z), (32, 3, 4));
*return_borrow_of_field_from_dropped_box_2(Box::new((&mut x, &mut y))) += 10;
assert_eq!((x, y, z), (42, 3, 4));
*return_borrow_from_dropped_tupled_box_1((Box::new((&mut x, &mut y)), &mut z)) += 10;
assert_eq!((x, y, z), (52, 3, 4));
*return_borrow_from_dropped_tupled_box_2((Box::new((&mut x, &mut y)), &mut z)) += 10;
assert_eq!((x, y, z), (62, 3, 4));
}
// These scribbling tests have been transcribed from
// issue-45696-scribble-on-boxed-borrow.rs
//
// In the context of that file, these tests are meant to show cases
// that should be *accepted* by the compiler, so here we are actually
// checking that the code we get when they are compiled matches our
// expectations.
struct Scribble<'a>(&'a mut u32);
impl<'a> Drop for Scribble<'a> { fn drop(&mut self) { *self.0 = 42; } }
// this is okay, in both AST-borrowck and NLL: The `Scribble` here *has*
// to strictly outlive `'a`
fn borrowed_scribble<'a>(s: &'a mut Scribble) -> &'a mut u32 {
&mut *s.0
}
// this, by analogy to previous case, is also okay.
fn boxed_borrowed_scribble<'a>(s: Box<&'a mut Scribble>) -> &'a mut u32 {
&mut *(*s).0
}
// this, by analogy to previous case, is also okay.
fn boxed_boxed_borrowed_scribble<'a>(s: Box<Box<&'a mut Scribble>>) -> &'a mut u32 {
&mut *(**s).0
}
fn scribbling_tests() {
let mut x = 1;
{
let mut long_lived = Scribble(&mut x);
*borrowed_scribble(&mut long_lived) += 10;
assert_eq!(*long_lived.0, 11);
// (Scribble dtor runs here, after `&mut`-borrow above ends)
}
assert_eq!(x, 42);
x = 1;
{
let mut long_lived = Scribble(&mut x);
*boxed_borrowed_scribble(Box::new(&mut long_lived)) += 10;
assert_eq!(*long_lived.0, 11);
// (Scribble dtor runs here, after `&mut`-borrow above ends)
}
assert_eq!(x, 42);
x = 1;
{
let mut long_lived = Scribble(&mut x);
*boxed_boxed_borrowed_scribble(Box::new(Box::new(&mut long_lived))) += 10;
assert_eq!(*long_lived.0, 11);
// (Scribble dtor runs here, after `&mut`-borrow above ends)
}
assert_eq!(x, 42);
}
fn main() {
basic_tests();
scribbling_tests();
}
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