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Rollup merge of rust-lang#59500 - crlf0710:boxed-closure-impls, r=cramertj
Unsized rvalues: implement boxed closure impls. (2nd try) This is a rebase of S-blocked-closed PR rust-lang#55431 to current master. LLVM has moved forward since then, so maybe we can check whether the new LLVM 8.0 version unblocked this work.
2 parents 8543a10 + 812d89c commit 20dcec2

12 files changed

+119
-100
lines changed

‎src/doc/unstable-book/src/library-features/fnbox.md‎

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# `fnbox`
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The tracking issue for this feature is [#28796]
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[#28796]: https://github.com/rust-lang/rust/issues/28796
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------------------------
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This had been a temporary alternative to the following impls:
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```rust,ignore
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impl<A, F> FnOnce for Box<F> where F: FnOnce<A> + ?Sized {}
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impl<A, F> FnMut for Box<F> where F: FnMut<A> + ?Sized {}
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impl<A, F> Fn for Box<F> where F: Fn<A> + ?Sized {}
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```
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The impls are parallel to these (relatively old) impls:
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```rust,ignore
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impl<A, F> FnOnce for &mut F where F: FnMut<A> + ?Sized {}
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impl<A, F> FnMut for &mut F where F: FnMut<A> + ?Sized {}
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impl<A, F> Fn for &mut F where F: Fn<A> + ?Sized {}
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impl<A, F> FnOnce for &F where F: Fn<A> + ?Sized {}
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impl<A, F> FnMut for &F where F: Fn<A> + ?Sized {}
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impl<A, F> Fn for &F where F: Fn<A> + ?Sized {}
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```
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Before the introduction of [`unsized_locals`][unsized_locals], we had been unable to provide the former impls. That means, unlike `&dyn Fn()` or `&mut dyn FnMut()` we could not use `Box<dyn FnOnce()>` at that time.
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[unsized_locals]: language-features/unsized-locals.html
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`FnBox()` is an alternative approach to `Box<dyn FnBox()>` is delegated to `FnBox::call_box` which doesn't need unsized locals. As we now have `Box<dyn FnOnce()>` working, the `fnbox` feature is going to be removed.

‎src/liballoc/boxed.rs‎

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@@ -694,6 +694,28 @@ impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {
694694
#[stable(feature = "fused", since = "1.26.0")]
695695
impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
696696

697+
#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
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impl<A, F: FnOnce<A> + ?Sized> FnOnce<A> for Box<F> {
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type Output = <F as FnOnce<A>>::Output;
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extern "rust-call" fn call_once(self, args: A) -> Self::Output {
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<F as FnOnce<A>>::call_once(*self, args)
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}
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}
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#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
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impl<A, F: FnMut<A> + ?Sized> FnMut<A> for Box<F> {
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extern "rust-call" fn call_mut(&mut self, args: A) -> Self::Output {
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<F as FnMut<A>>::call_mut(self, args)
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}
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}
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#[stable(feature = "boxed_closure_impls", since = "1.35.0")]
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impl<A, F: Fn<A> + ?Sized> Fn<A> for Box<F> {
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extern "rust-call" fn call(&self, args: A) -> Self::Output {
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<F as Fn<A>>::call(self, args)
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}
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}
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698720
/// `FnBox` is a version of the `FnOnce` intended for use with boxed
699721
/// closure objects. The idea is that where one would normally store a
@@ -735,9 +757,7 @@ impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
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#[rustc_paren_sugar]
736758
#[unstable(feature = "fnbox",
737759
reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
738-
pub trait FnBox<A> {
739-
type Output;
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pub trait FnBox<A>: FnOnce<A> {
741761
fn call_box(self: Box<Self>, args: A) -> Self::Output;
742762
}
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@@ -746,33 +766,11 @@ pub trait FnBox<A> {
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impl<A, F> FnBox<A> for F
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where F: FnOnce<A>
748768
{
749-
type Output = F::Output;
750-
751769
fn call_box(self: Box<F>, args: A) -> F::Output {
752770
self.call_once(args)
753771
}
754772
}
755773

756-
#[unstable(feature = "fnbox",
757-
reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
758-
impl<A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + '_> {
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type Output = R;
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extern "rust-call" fn call_once(self, args: A) -> R {
762-
self.call_box(args)
763-
}
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}
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#[unstable(feature = "fnbox",
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reason = "will be deprecated if and when `Box<FnOnce>` becomes usable", issue = "28796")]
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impl<A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + Send + '_> {
769-
type Output = R;
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extern "rust-call" fn call_once(self, args: A) -> R {
772-
self.call_box(args)
773-
}
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}
775-
776774
#[unstable(feature = "coerce_unsized", issue = "27732")]
777775
impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}
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‎src/liballoc/lib.rs‎

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#![feature(unboxed_closures)]
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#![feature(unicode_internals)]
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#![feature(unsize)]
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#![feature(unsized_locals)]
110111
#![feature(allocator_internals)]
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#![feature(on_unimplemented)]
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#![feature(rustc_const_unstable)]

‎src/test/run-pass/unsized-locals/box-fnonce.rs‎

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fn call_it<T>(f: Box<dyn FnOnce() -> T>) -> T {
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f()
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}
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fn main() {
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let s = "hello".to_owned();
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assert_eq!(&call_it(Box::new(|| s)) as &str, "hello");
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}

‎src/test/run-pass/unsized-locals/fnbox-compat.rs‎

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#![feature(fnbox)]
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use std::boxed::FnBox;
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fn call_it<T>(f: Box<dyn FnBox() -> T>) -> T {
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f()
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}
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fn main() {
10+
let s = "hello".to_owned();
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assert_eq!(&call_it(Box::new(|| s)) as &str, "hello");
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}

‎src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.nll.stderr‎

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@@ -7,17 +7,15 @@ LL | f(f(10));
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| first mutable borrow occurs here
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| first borrow later used by call
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10-
error[E0382]: use of moved value: `*f`
10+
error[E0382]: use of moved value: `f`
1111
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
1212
|
1313
LL | fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
14-
| - consider adding a `Copy` constraint to this type argument
14+
| - move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
1515
LL | f(f(10));
1616
| - ^ value used here after move
1717
| |
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| value moved here
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|
20-
= note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
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2220
error[E0499]: cannot borrow `*f` as mutable more than once at a time
2321
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
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2826
| first mutable borrow occurs here
2927
| first borrow later used by call
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31-
error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
32-
--> $DIR/two-phase-nonrecv-autoref.rs:85:9
33-
|
34-
LL | f(f(10));
35-
| ^
36-
37-
error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
38-
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
39-
|
40-
LL | f(f(10));
41-
| ^
42-
43-
error[E0382]: use of moved value: `*f`
29+
error[E0382]: use of moved value: `f`
4430
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
4531
|
32+
LL | fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
33+
| - move occurs because `f` has type `std::boxed::Box<dyn std::ops::FnOnce(i32) -> i32>`, which does not implement the `Copy` trait
4634
LL | f(f(10));
4735
| - ^ value used here after move
4836
| |
4937
| value moved here
50-
|
51-
= note: move occurs because `*f` has type `dyn std::ops::FnOnce(i32) -> i32`, which does not implement the `Copy` trait
5238

5339
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
54-
--> $DIR/two-phase-nonrecv-autoref.rs:129:27
40+
--> $DIR/two-phase-nonrecv-autoref.rs:125:27
5541
|
5642
LL | double_access(&mut a, &a);
5743
| ------------- ------ ^^ immutable borrow occurs here
@@ -60,7 +46,7 @@ LL | double_access(&mut a, &a);
6046
| mutable borrow later used by call
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6248
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
63-
--> $DIR/two-phase-nonrecv-autoref.rs:157:7
49+
--> $DIR/two-phase-nonrecv-autoref.rs:153:7
6450
|
6551
LL | i[i[3]] = 4;
6652
| --^----
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7056
| mutable borrow later used here
7157

7258
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
73-
--> $DIR/two-phase-nonrecv-autoref.rs:163:7
59+
--> $DIR/two-phase-nonrecv-autoref.rs:159:7
7460
|
7561
LL | i[i[3]] = i[4];
7662
| --^----
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7965
| mutable borrow occurs here
8066
| mutable borrow later used here
8167

82-
error: aborting due to 9 previous errors
68+
error: aborting due to 7 previous errors
8369

84-
Some errors occurred: E0161, E0382, E0499, E0502.
85-
For more information about an error, try `rustc --explain E0161`.
70+
Some errors occurred: E0382, E0499, E0502.
71+
For more information about an error, try `rustc --explain E0382`.

‎src/test/ui/borrowck/two-phase-nonrecv-autoref.ast.stderr‎

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@@ -15,15 +15,15 @@ LL | f(f(10));
1515
| | second mutable borrow occurs here
1616
| first mutable borrow occurs here
1717

18-
error[E0382]: use of moved value: `*f`
18+
error[E0382]: use of moved value: `f`
1919
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
2020
|
2121
LL | f(f(10));
2222
| - ^ value used here after move
2323
| |
2424
| value moved here
2525
|
26-
= note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
26+
= note: move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
2727

2828
error[E0499]: cannot borrow `*f` as mutable more than once at a time
2929
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
@@ -34,18 +34,18 @@ LL | f(f(10));
3434
| | second mutable borrow occurs here
3535
| first mutable borrow occurs here
3636

37-
error[E0382]: use of moved value: `*f`
37+
error[E0382]: use of moved value: `f`
3838
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
3939
|
4040
LL | f(f(10));
4141
| - ^ value used here after move
4242
| |
4343
| value moved here
4444
|
45-
= note: move occurs because `*f` has type `(dyn std::ops::FnOnce(i32) -> i32 + 'static)`, which does not implement the `Copy` trait
45+
= note: move occurs because `f` has type `std::boxed::Box<(dyn std::ops::FnOnce(i32) -> i32 + 'static)>`, which does not implement the `Copy` trait
4646

4747
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
48-
--> $DIR/two-phase-nonrecv-autoref.rs:129:28
48+
--> $DIR/two-phase-nonrecv-autoref.rs:125:28
4949
|
5050
LL | double_access(&mut a, &a);
5151
| - ^- mutable borrow ends here
@@ -54,7 +54,7 @@ LL | double_access(&mut a, &a);
5454
| mutable borrow occurs here
5555

5656
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
57-
--> $DIR/two-phase-nonrecv-autoref.rs:135:9
57+
--> $DIR/two-phase-nonrecv-autoref.rs:131:9
5858
|
5959
LL | a.m(a.i(10));
6060
| - ^ - mutable borrow ends here
@@ -63,7 +63,7 @@ LL | a.m(a.i(10));
6363
| mutable borrow occurs here
6464

6565
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
66-
--> $DIR/two-phase-nonrecv-autoref.rs:157:7
66+
--> $DIR/two-phase-nonrecv-autoref.rs:153:7
6767
|
6868
LL | i[i[3]] = 4;
6969
| - ^ - mutable borrow ends here
@@ -72,7 +72,7 @@ LL | i[i[3]] = 4;
7272
| mutable borrow occurs here
7373

7474
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
75-
--> $DIR/two-phase-nonrecv-autoref.rs:163:7
75+
--> $DIR/two-phase-nonrecv-autoref.rs:159:7
7676
|
7777
LL | i[i[3]] = i[4];
7878
| - ^ - mutable borrow ends here
@@ -81,7 +81,7 @@ LL | i[i[3]] = i[4];
8181
| mutable borrow occurs here
8282

8383
error[E0502]: cannot borrow `v` as immutable because it is also borrowed as mutable
84-
--> $DIR/two-phase-nonrecv-autoref.rs:172:12
84+
--> $DIR/two-phase-nonrecv-autoref.rs:168:12
8585
|
8686
LL | v.push(v.len());
8787
| - ^ - mutable borrow ends here
@@ -90,7 +90,7 @@ LL | v.push(v.len());
9090
| mutable borrow occurs here
9191

9292
error[E0502]: cannot borrow `s` as immutable because it is also borrowed as mutable
93-
--> $DIR/two-phase-nonrecv-autoref.rs:183:9
93+
--> $DIR/two-phase-nonrecv-autoref.rs:179:9
9494
|
9595
LL | s.m(s.i(10));
9696
| - ^ - mutable borrow ends here
@@ -99,7 +99,7 @@ LL | s.m(s.i(10));
9999
| mutable borrow occurs here
100100

101101
error[E0502]: cannot borrow `t` as immutable because it is also borrowed as mutable
102-
--> $DIR/two-phase-nonrecv-autoref.rs:188:9
102+
--> $DIR/two-phase-nonrecv-autoref.rs:184:9
103103
|
104104
LL | t.m(t.i(10));
105105
| - ^ - mutable borrow ends here

‎src/test/ui/borrowck/two-phase-nonrecv-autoref.nll.stderr‎

Lines changed: 11 additions & 25 deletions
Original file line numberDiff line numberDiff line change
@@ -7,17 +7,15 @@ LL | f(f(10));
77
| first mutable borrow occurs here
88
| first borrow later used by call
99

10-
error[E0382]: use of moved value: `*f`
10+
error[E0382]: use of moved value: `f`
1111
--> $DIR/two-phase-nonrecv-autoref.rs:69:11
1212
|
1313
LL | fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
14-
| - consider adding a `Copy` constraint to this type argument
14+
| - move occurs because `f` has type `std::boxed::Box<F>`, which does not implement the `Copy` trait
1515
LL | f(f(10));
1616
| - ^ value used here after move
1717
| |
1818
| value moved here
19-
|
20-
= note: move occurs because `*f` has type `F`, which does not implement the `Copy` trait
2119

2220
error[E0499]: cannot borrow `*f` as mutable more than once at a time
2321
--> $DIR/two-phase-nonrecv-autoref.rs:76:11
@@ -28,30 +26,18 @@ LL | f(f(10));
2826
| first mutable borrow occurs here
2927
| first borrow later used by call
3028

31-
error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
32-
--> $DIR/two-phase-nonrecv-autoref.rs:85:9
33-
|
34-
LL | f(f(10));
35-
| ^
36-
37-
error[E0161]: cannot move a value of type dyn std::ops::FnOnce(i32) -> i32: the size of dyn std::ops::FnOnce(i32) -> i32 cannot be statically determined
38-
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
39-
|
40-
LL | f(f(10));
41-
| ^
42-
43-
error[E0382]: use of moved value: `*f`
29+
error[E0382]: use of moved value: `f`
4430
--> $DIR/two-phase-nonrecv-autoref.rs:85:11
4531
|
32+
LL | fn twice_ten_oo(f: Box<FnOnce(i32) -> i32>) {
33+
| - move occurs because `f` has type `std::boxed::Box<dyn std::ops::FnOnce(i32) -> i32>`, which does not implement the `Copy` trait
4634
LL | f(f(10));
4735
| - ^ value used here after move
4836
| |
4937
| value moved here
50-
|
51-
= note: move occurs because `*f` has type `dyn std::ops::FnOnce(i32) -> i32`, which does not implement the `Copy` trait
5238

5339
error[E0502]: cannot borrow `a` as immutable because it is also borrowed as mutable
54-
--> $DIR/two-phase-nonrecv-autoref.rs:129:27
40+
--> $DIR/two-phase-nonrecv-autoref.rs:125:27
5541
|
5642
LL | double_access(&mut a, &a);
5743
| ------------- ------ ^^ immutable borrow occurs here
@@ -60,7 +46,7 @@ LL | double_access(&mut a, &a);
6046
| mutable borrow later used by call
6147

6248
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
63-
--> $DIR/two-phase-nonrecv-autoref.rs:157:7
49+
--> $DIR/two-phase-nonrecv-autoref.rs:153:7
6450
|
6551
LL | i[i[3]] = 4;
6652
| --^----
@@ -70,7 +56,7 @@ LL | i[i[3]] = 4;
7056
| mutable borrow later used here
7157

7258
error[E0502]: cannot borrow `i` as immutable because it is also borrowed as mutable
73-
--> $DIR/two-phase-nonrecv-autoref.rs:163:7
59+
--> $DIR/two-phase-nonrecv-autoref.rs:159:7
7460
|
7561
LL | i[i[3]] = i[4];
7662
| --^----
@@ -79,7 +65,7 @@ LL | i[i[3]] = i[4];
7965
| mutable borrow occurs here
8066
| mutable borrow later used here
8167

82-
error: aborting due to 9 previous errors
68+
error: aborting due to 7 previous errors
8369

84-
Some errors occurred: E0161, E0382, E0499, E0502.
85-
For more information about an error, try `rustc --explain E0161`.
70+
Some errors occurred: E0382, E0499, E0502.
71+
For more information about an error, try `rustc --explain E0382`.

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