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Diffstat (limited to 'tests/ui/nll/issue-45696-scribble-on-boxed-borrow.rs')
-rw-r--r-- | tests/ui/nll/issue-45696-scribble-on-boxed-borrow.rs | 67 |
1 files changed, 67 insertions, 0 deletions
diff --git a/tests/ui/nll/issue-45696-scribble-on-boxed-borrow.rs b/tests/ui/nll/issue-45696-scribble-on-boxed-borrow.rs new file mode 100644 index 000000000..637cf278f --- /dev/null +++ b/tests/ui/nll/issue-45696-scribble-on-boxed-borrow.rs @@ -0,0 +1,67 @@ +// 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. + +// ignore-compare-mode-polonius + +struct Scribble<'a>(&'a mut u32); + +impl<'a> Drop for Scribble<'a> { fn drop(&mut self) { *self.0 = 42; } } + +// this is okay: 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.) +fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 { + &mut *s.0 //~ ERROR borrow may still be in use when destructor runs [E0713] +} + +// This, by analogy to previous case, is *also* not okay. +fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 { + &mut *(*s).0 //~ ERROR borrow may still be in use when destructor runs [E0713] +} + +// This, by analogy to previous case, is *also* not okay. +fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 { + &mut *(**s).0 //~ ERROR borrow may still be in use when destructor runs [E0713] +} + +fn main() { + 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; +} |