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