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