| // rust-lang/rust#45696: This test is checking that we *cannot* return |
| // mutable borrows that would be scribbled over by destructors before |
| // the return occurs. |
| // |
| // We will explicitly test NLL, and migration modes; |
| // thus we will also skip the automated compare-mode=nll. |
| |
| // revisions: nll migrate |
| // ignore-compare-mode-nll |
| // ignore-compare-mode-polonius |
| |
| // This test is going to pass in the migrate revision, because the AST-borrowck |
| // accepted this code in the past (see notes below). So we use `#[rustc_error]` |
| // to keep the outcome as an error in all scenarios, and rely on the stderr |
| // files to show what the actual behavior is. (See rust-lang/rust#49855.) |
| #![feature(rustc_attrs)] |
| |
| #![cfg_attr(nll, feature(nll))] |
| |
| 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 |
| } |
| |
| // this is not okay: in between the time that we take the mutable |
| // borrow and the caller receives it as a return value, the drop of |
| // `s` will scribble on it, violating our aliasing guarantees. |
| // |
| // * (Maybe in the future the two-phase borrows system will be |
| // extended to support this case. But for now, it is an error in |
| // NLL, even with two-phase borrows.) |
| // |
| // In any case, the AST-borrowck was not smart enough to know that |
| // this should be an error. (Which is perhaps the essence of why |
| // rust-lang/rust#45696 arose in the first place.) |
| fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 { |
| &mut *s.0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713] |
| //[migrate]~^ WARNING borrow may still be in use when destructor runs [E0713] |
| //[migrate]~| WARNING this error has been downgraded to a warning for backwards compatibility |
| //[migrate]~| WARNING this represents potential undefined behavior in your code |
| } |
| |
| // This, by analogy to previous case, is *also* not okay. |
| // |
| // (But again, AST-borrowck was not smart enogh to know that this |
| // should be an error.) |
| fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 { |
| &mut *(*s).0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713] |
| //[migrate]~^ WARNING borrow may still be in use when destructor runs [E0713] |
| //[migrate]~| WARNING this error has been downgraded to a warning for backwards compatibility |
| //[migrate]~| WARNING this represents potential undefined behavior in your code |
| } |
| |
| // This, by analogy to previous case, is *also* not okay. |
| // |
| // (But again, AST-borrowck was not smart enogh to know that this |
| // should be an error.) |
| fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 { |
| &mut *(**s).0 //[nll]~ ERROR borrow may still be in use when destructor runs [E0713] |
| //[migrate]~^ WARNING borrow may still be in use when destructor runs [E0713] |
| //[migrate]~| WARNING this error has been downgraded to a warning for backwards compatibility |
| //[migrate]~| WARNING this represents potential undefined behavior in your code |
| } |
| |
| #[rustc_error] |
| fn main() { //[migrate]~ ERROR compilation successful |
| let mut x = 1; |
| { |
| let mut long_lived = Scribble(&mut x); |
| *borrowed_scribble(&mut long_lived) += 10; |
| // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| } |
| { |
| let mut long_lived = Scribble(&mut x); |
| *boxed_borrowed_scribble(Box::new(&mut long_lived)) += 10; |
| // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| } |
| { |
| let mut long_lived = Scribble(&mut x); |
| *boxed_boxed_borrowed_scribble(Box::new(Box::new(&mut long_lived))) += 10; |
| // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| } |
| *scribbled(Scribble(&mut x)) += 10; |
| *boxed_scribbled(Box::new(Scribble(&mut x))) += 10; |
| *boxed_boxed_scribbled(Box::new(Box::new(Scribble(&mut x)))) += 10; |
| } |