1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
|
// revisions: base
//[g2p]compile-flags: -Z two-phase-beyond-autoref
// the above revision is disabled until two-phase-beyond-autoref support is better
// This is a test checking that when we limit two-phase borrows to
// method receivers, we do not let other kinds of auto-ref to leak
// through.
//
// The g2p revision illustrates the "undesirable" behavior you would
// otherwise observe without limiting the phasing to autoref on method
// receivers (namely, in many cases demonstrated below, the error
// would not arise).
use std::ops::{Index, IndexMut};
fn foo(x: &mut u32, y: u32) {
*x += y;
}
fn deref_coercion(x: &mut u32) {
foo(x, *x);
// Above error is a known limitation of AST borrowck
}
// While adding a flag to adjustments (indicating whether they
// should support two-phase borrows, here are the cases I
// encountered:
//
// - [x] Resolving overloaded_call_traits (call, call_mut, call_once)
// - [x] deref_coercion (shown above)
// - [x] coerce_unsized e.g., `&[T; n]`, `&mut [T; n] -> &[T]`,
// `&mut [T; n] -> &mut [T]`, `&Concrete -> &Trait`
// - [x] Method Call Receivers (the case we want to support!)
// - [x] ExprKind::Index and ExprKind::Unary Deref; only need to handle coerce_index_op
// - [x] overloaded_binops
fn overloaded_call_traits() {
// Regarding overloaded call traits, note that there is no
// scenario where adding two-phase borrows should "fix" these
// cases, because either we will resolve both invocations to
// `call_mut` (in which case the inner call requires a mutable
// borrow which will conflict with the outer reservation), or we
// will resolve both to `call` (which will just work, regardless
// of two-phase borrow support), or we will resolve both to
// `call_once` (in which case the inner call requires moving the
// receiver, invalidating the outer call).
fn twice_ten_sm<F: FnMut(i32) -> i32>(f: &mut F) {
f(f(10));
//~^ ERROR cannot borrow `*f` as mutable more than once at a time
}
fn twice_ten_si<F: Fn(i32) -> i32>(f: &mut F) {
f(f(10));
}
fn twice_ten_so<F: FnOnce(i32) -> i32>(f: Box<F>) {
f(f(10));
//~^ ERROR use of moved value: `f`
}
fn twice_ten_om(f: &mut dyn FnMut(i32) -> i32) {
f(f(10));
//~^ ERROR cannot borrow `*f` as mutable more than once at a time
}
fn twice_ten_oi(f: &mut dyn Fn(i32) -> i32) {
f(f(10));
}
fn twice_ten_oo(f: Box<dyn FnOnce(i32) -> i32>) {
f(f(10));
//~^ ERROR use of moved value: `f`
}
twice_ten_sm(&mut |x| x + 1);
twice_ten_si(&mut |x| x + 1);
twice_ten_so(Box::new(|x| x + 1));
twice_ten_om(&mut |x| x + 1);
twice_ten_oi(&mut |x| x + 1);
twice_ten_oo(Box::new(|x| x + 1));
}
trait TwoMethods {
fn m(&mut self, x: i32) -> i32 { x + 1 }
fn i(&self, x: i32) -> i32 { x + 1 }
}
struct T;
impl TwoMethods for T { }
struct S;
impl S {
fn m(&mut self, x: i32) -> i32 { x + 1 }
fn i(&self, x: i32) -> i32 { x + 1 }
}
impl TwoMethods for [i32; 3] { }
fn double_access<X: Copy>(m: &mut [X], s: &[X]) {
m[0] = s[1];
}
fn coerce_unsized() {
let mut a = [1, 2, 3];
// This is not okay.
double_access(&mut a, &a);
//~^ ERROR cannot borrow `a` as immutable because it is also borrowed as mutable [E0502]
// But this is okay.
a.m(a.i(10));
// Above error is an expected limitation of AST borrowck
}
struct I(i32);
impl Index<i32> for I {
type Output = i32;
fn index(&self, _: i32) -> &i32 {
&self.0
}
}
impl IndexMut<i32> for I {
fn index_mut(&mut self, _: i32) -> &mut i32 {
&mut self.0
}
}
fn coerce_index_op() {
let mut i = I(10);
i[i[3]] = 4;
//~^ ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
// Should be accepted with g2p
i[3] = i[4];
i[i[3]] = i[4];
//~^ ERROR cannot borrow `i` as immutable because it is also borrowed as mutable [E0502]
// Should be accepted with g2p
}
fn main() {
// As a reminder, this is the basic case we want to ensure we handle.
let mut v = vec![1, 2, 3];
v.push(v.len());
// Error above is an expected limitation of AST borrowck
// (as a rule, pnkfelix does not like to write tests with dead code.)
deref_coercion(&mut 5);
overloaded_call_traits();
let mut s = S;
s.m(s.i(10));
// Error above is an expected limitation of AST borrowck
let mut t = T;
t.m(t.i(10));
// Error above is an expected limitation of AST borrowck
coerce_unsized();
coerce_index_op();
}
|
