--- /dev/null
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// rust-lang/rust#45696: This test is checking that we can return
+// mutable borrows owned by boxes even when the boxes are dropped.
+//
+// We will explicitly test AST-borrowck, NLL, and migration modes;
+// thus we will also skip the automated compare-mode=nll.
+
+// revisions: ast nll migrate
+// ignore-compare-mode-nll
+
+#![cfg_attr(nll, feature(nll))]
+//[migrate]compile-flags: -Z borrowck=migrate -Z two-phase-borrows
+
+// run-pass
+
+type Boxed<'a, 'b> = Box<(&'a mut u32, &'b mut u32)>;
+
+fn return_borrow_from_dropped_box<'a>(x: Boxed<'a, '_>) -> &'a mut u32 {
+ &mut *x.0
+}
+
+fn return_borrow_from_dropped_tupled_box<'a>(x: (Boxed<'a, '_>, &mut u32)) -> &'a mut u32 {
+ &mut *(x.0).0
+}
+
+fn basic_tests() {
+ let mut x = 2;
+ let mut y = 3;
+ let mut z = 4;
+ *return_borrow_from_dropped_box(Box::new((&mut x, &mut y))) += 10;
+ assert_eq!((x, y, z), (12, 3, 4));
+ *return_borrow_from_dropped_tupled_box((Box::new((&mut x, &mut y)), &mut z)) += 10;
+ assert_eq!((x, y, z), (22, 3, 4));
+}
+
+// These scribbling tests have been transcribed from
+// issue-45696-scribble-on-boxed-borrow.rs
+//
+// In the context of that file, these tests are meant to show cases
+// that should be *accepted* by the compiler, so here we are actually
+// checking that the code we get when they are compiled matches our
+// expectations.
+
+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
+}
+
+fn scribbling_tests() {
+ let mut x = 1;
+ {
+ let mut long_lived = Scribble(&mut x);
+ *borrowed_scribble(&mut long_lived) += 10;
+ assert_eq!(*long_lived.0, 11);
+ // (Scribble dtor runs here, after `&mut`-borrow above ends)
+ }
+ assert_eq!(x, 42);
+ x = 1;
+ {
+ let mut long_lived = Scribble(&mut x);
+ *boxed_borrowed_scribble(Box::new(&mut long_lived)) += 10;
+ assert_eq!(*long_lived.0, 11);
+ // (Scribble dtor runs here, after `&mut`-borrow above ends)
+ }
+ assert_eq!(x, 42);
+ x = 1;
+ {
+ let mut long_lived = Scribble(&mut x);
+ *boxed_boxed_borrowed_scribble(Box::new(Box::new(&mut long_lived))) += 10;
+ assert_eq!(*long_lived.0, 11);
+ // (Scribble dtor runs here, after `&mut`-borrow above ends)
+ }
+ assert_eq!(x, 42);
+}
+
+fn main() {
+ basic_tests();
+ scribbling_tests();
+}
--- /dev/null
+error: compilation successful
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:89:1
+ |
+LL | / fn main() { //[ast]~ ERROR compilation successful
+LL | | //[migrate]~^ ERROR compilation successful
+LL | | let mut x = 1;
+LL | | {
+... |
+LL | | *boxed_boxed_scribbled(Box::new(Box::new(Scribble(&mut x)))) += 10;
+LL | | }
+ | |_^
+
+error: aborting due to previous error
+
--- /dev/null
+warning[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:63:5
+ |
+LL | &mut *s.0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 62:14...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:62:14
+ |
+LL | fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 {
+ | ^^
+ = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
+ It represents potential unsoundness in your code.
+ This warning will become a hard error in the future.
+
+warning[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:73:5
+ |
+LL | &mut *(*s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 72:20...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:72:20
+ |
+LL | fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 {
+ | ^^
+ = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
+ It represents potential unsoundness in your code.
+ This warning will become a hard error in the future.
+
+warning[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:83:5
+ |
+LL | &mut *(**s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 82:26...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:82:26
+ |
+LL | fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 {
+ | ^^
+ = warning: This error has been downgraded to a warning for backwards compatibility with previous releases.
+ It represents potential unsoundness in your code.
+ This warning will become a hard error in the future.
+
+error: compilation successful
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:89:1
+ |
+LL | / fn main() { //[ast]~ ERROR compilation successful
+LL | | //[migrate]~^ ERROR compilation successful
+LL | | let mut x = 1;
+LL | | {
+... |
+LL | | *boxed_boxed_scribbled(Box::new(Box::new(Scribble(&mut x)))) += 10;
+LL | | }
+ | |_^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0597`.
--- /dev/null
+error[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:63:5
+ |
+LL | &mut *s.0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 62:14...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:62:14
+ |
+LL | fn scribbled<'a>(s: Scribble<'a>) -> &'a mut u32 {
+ | ^^
+
+error[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:73:5
+ |
+LL | &mut *(*s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 72:20...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:72:20
+ |
+LL | fn boxed_scribbled<'a>(s: Box<Scribble<'a>>) -> &'a mut u32 {
+ | ^^
+
+error[E0597]: `*s.0` does not live long enough
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:83:5
+ |
+LL | &mut *(**s).0 //[nll]~ ERROR `*s.0` does not live long enough [E0597]
+ | ^^^^^^^^^^^^^ borrowed value does not live long enough
+...
+LL | }
+ | - `*s.0` dropped here while still borrowed
+ |
+note: borrowed value must be valid for the lifetime 'a as defined on the function body at 82:26...
+ --> $DIR/issue-45696-scribble-on-boxed-borrow.rs:82:26
+ |
+LL | fn boxed_boxed_scribbled<'a>(s: Box<Box<Scribble<'a>>>) -> &'a mut u32 {
+ | ^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0597`.
--- /dev/null
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// 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 AST-borrowck, NLL, and migration modes;
+// thus we will also skip the automated compare-mode=nll.
+
+// revisions: ast nll migrate
+// ignore-compare-mode-nll
+
+// This test is going to pass in the ast and migrate revisions,
+// 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))]
+//[migrate]compile-flags: -Z borrowck=migrate -Z two-phase-borrows
+
+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 `*s.0` does not live long enough [E0597]
+ //[migrate]~^ WARNING `*s.0` does not live long enough [E0597]
+ //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility
+}
+
+// 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 `*s.0` does not live long enough [E0597]
+ //[migrate]~^ WARNING `*s.0` does not live long enough [E0597]
+ //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility
+}
+
+// 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 `*s.0` does not live long enough [E0597]
+ //[migrate]~^ WARNING `*s.0` does not live long enough [E0597]
+ //[migrate]~| WARNING This error has been downgraded to a warning for backwards compatibility
+}
+
+#[rustc_error]
+fn main() { //[ast]~ ERROR compilation successful
+ //[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;
+}
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