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| 1 | +// Copyright 2018 The Rust Project Developers. See the COPYRIGHT |
| 2 | +// file at the top-level directory of this distribution and at |
| 3 | +// http://rust-lang.org/COPYRIGHT. |
| 4 | +// |
| 5 | +// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or |
| 6 | +// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license |
| 7 | +// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your |
| 8 | +// option. This file may not be copied, modified, or distributed |
| 9 | +// except according to those terms. |
| 10 | + |
| 11 | +// rust-lang/rust#45696: This test is checking that we *cannot* return |
| 12 | +// mutable borrows that would be scribbled over by destructors before |
| 13 | +// the return occurs. |
| 14 | +// |
| 15 | +// We will explicitly test AST-borrowck, NLL, and migration modes; |
| 16 | +// thus we will also skip the automated compare-mode=nll. |
| 17 | + |
| 18 | +// revisions: ast nll migrate |
| 19 | +// ignore-compare-mode-nll |
| 20 | + |
| 21 | +// This test is going to pass in the ast and migrate revisions, |
| 22 | +// because the AST-borrowck accepted this code in the past (see notes |
| 23 | +// below). So we use `#[rustc_error]` to keep the outcome as an error |
| 24 | +// in all scenarios, and rely on the stderr files to show what the |
| 25 | +// actual behavior is. (See rust-lang/rust#49855.) |
| 26 | +#![feature(rustc_attrs)] |
| 27 | + |
| 28 | +#![cfg_attr(nll, feature(nll))] |
| 29 | +//[migrate]compile-flags: -Z borrowck=migrate -Z two-phase-borrows |
| 30 | + |
| 31 | +struct Scribble<'a>(&'a mut u32); |
| 32 | + |
| 33 | +impl<'a> Drop for Scribble<'a> { fn drop(&mut self) { *self.0 = 42; } } |
| 34 | + |
| 35 | +// this is okay, in both AST-borrowck and NLL: The `Scribble` here *has* |
| 36 | +// to strictly outlive `'a` |
| 37 | +fn borrowed_scribble<'a>(s: &'a mut Scribble) -> &'a mut u32 { |
| 38 | + &mut *s.0 |
| 39 | +} |
| 40 | + |
| 41 | +// this, by analogy to previous case, is also okay. |
| 42 | +fn boxed_borrowed_scribble<'a>(s: Box<&'a mut Scribble>) -> &'a mut u32 { |
| 43 | + &mut *(*s).0 |
| 44 | +} |
| 45 | + |
| 46 | +// this, by analogy to previous case, is also okay. |
| 47 | +fn boxed_boxed_borrowed_scribble<'a>(s: Box<Box<&'a mut Scribble>>) -> &'a mut u32 { |
| 48 | + &mut *(**s).0 |
| 49 | +} |
| 50 | + |
| 51 | +// this is not okay: in between the time that we take the mutable |
| 52 | +// borrow and the caller receives it as a return value, the drop of |
| 53 | +// `s` will scribble on it, violating our aliasing guarantees. |
| 54 | +// |
| 55 | +// * (Maybe in the future the two-phase borrows system will be |
| 56 | +// extended to support this case. But for now, it is an error in |
| 57 | +// NLL, even with two-phase borrows.) |
| 58 | +// |
| 59 | +// In any case, the AST-borrowck was not smart enough to know that |
| 60 | +// this should be an error. (Which is perhaps the essence of why |
| 61 | +// rust-lang/rust#45696 arose in the first place.) |
| 62 | +fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 { |
| 63 | + &mut *s.0 //[nll]~ ERROR `*s.0` does not live long enough [E0597] |
| 64 | + //[migrate]~^ WARNING `*s.0` does not live long enough [E0597] |
| 65 | + //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility |
| 66 | +} |
| 67 | + |
| 68 | +// This, by analogy to previous case, is *also* not okay. |
| 69 | +// |
| 70 | +// (But again, AST-borrowck was not smart enogh to know that this |
| 71 | +// should be an error.) |
| 72 | +fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 { |
| 73 | + &mut *(*s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597] |
| 74 | + //[migrate]~^ WARNING `*s.0` does not live long enough [E0597] |
| 75 | + //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility |
| 76 | +} |
| 77 | + |
| 78 | +// This, by analogy to previous case, is *also* not okay. |
| 79 | +// |
| 80 | +// (But again, AST-borrowck was not smart enogh to know that this |
| 81 | +// should be an error.) |
| 82 | +fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 { |
| 83 | + &mut *(**s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597] |
| 84 | + //[migrate]~^ WARNING `*s.0` does not live long enough [E0597] |
| 85 | + //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility |
| 86 | +} |
| 87 | + |
| 88 | +#[rustc_error] |
| 89 | +fn main() { //[ast]~ ERROR compilation successful |
| 90 | + //[migrate]~^ ERROR compilation successful |
| 91 | + let mut x = 1; |
| 92 | + { |
| 93 | + let mut long_lived = Scribble(&mut x); |
| 94 | + *borrowed_scribble(&mut long_lived) += 10; |
| 95 | + // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| 96 | + } |
| 97 | + { |
| 98 | + let mut long_lived = Scribble(&mut x); |
| 99 | + *boxed_borrowed_scribble(Box::new(&mut long_lived)) += 10; |
| 100 | + // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| 101 | + } |
| 102 | + { |
| 103 | + let mut long_lived = Scribble(&mut x); |
| 104 | + *boxed_boxed_borrowed_scribble(Box::new(Box::new(&mut long_lived))) += 10; |
| 105 | + // (Scribble dtor runs here, after `&mut`-borrow above ends) |
| 106 | + } |
| 107 | + *scribbled(Scribble(&mut x)) += 10; |
| 108 | + *boxed_scribbled(Box::new(Scribble(&mut x))) += 10; |
| 109 | + *boxed_boxed_scribbled(Box::new(Box::new(Scribble(&mut x)))) += 10; |
| 110 | +} |
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