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RalfJungRalfJung
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static mut: allow reference to arbitrary types, not just slices and arrays
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8 files changed

+46
-67
lines changed

8 files changed

+46
-67
lines changed

Diff for: ‎compiler/rustc_const_eval/src/transform/check_consts/check.rs

+16-24
Original file line numberDiff line numberDiff line change
@@ -476,35 +476,27 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
476476
}
477477
}
478478

479-
Rvalue::Ref(_, BorrowKind::Mut { .. }, place) => {
480-
let ty = place.ty(self.body, self.tcx).ty;
481-
let is_allowed = match ty.kind() {
482-
// Inside a `static mut`, `&mut [...]` is allowed.
483-
ty::Array(..) | ty::Slice(_)
484-
if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
485-
{
486-
true
487-
}
488-
489-
// FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
490-
// that this is merely a ZST and it is already eligible for promotion.
491-
// This may require an RFC?
492-
/*
493-
ty::Array(_, len) if len.try_eval_target_usize(cx.tcx, cx.param_env) == Some(0)
494-
=> true,
495-
*/
496-
_ => false,
497-
};
479+
Rvalue::Ref(_, BorrowKind::Mut { .. }, place)
480+
| Rvalue::AddressOf(Mutability::Mut, place) => {
481+
// Inside mutable statics, we allow arbitrary mutable references.
482+
// We've allowed `static mut FOO = &mut [elements];` for a long time (the exact
483+
// reasons why are lost to history), and there is no reason to restrict that to
484+
// arrays and slices.
485+
let is_allowed =
486+
self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut);
498487

499488
if !is_allowed {
500-
self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
489+
self.check_mut_borrow(
490+
place.local,
491+
if matches!(rvalue, Rvalue::Ref(..)) {
492+
hir::BorrowKind::Ref
493+
} else {
494+
hir::BorrowKind::Raw
495+
},
496+
);
501497
}
502498
}
503499

504-
Rvalue::AddressOf(Mutability::Mut, place) => {
505-
self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
506-
}
507-
508500
Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Fake, place)
509501
| Rvalue::AddressOf(Mutability::Not, place) => {
510502
let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(

Diff for: ‎tests/ui/array-slice-vec/check-static-mut-slices.rs

-15
This file was deleted.

Diff for: ‎tests/ui/consts/const-address-of-mut.rs

-2
Original file line numberDiff line numberDiff line change
@@ -4,8 +4,6 @@ const A: () = { let mut x = 2; &raw mut x; }; //~ mutable pointer
44

55
static B: () = { let mut x = 2; &raw mut x; }; //~ mutable pointer
66

7-
static mut C: () = { let mut x = 2; &raw mut x; }; //~ mutable pointer
8-
97
const fn foo() {
108
let mut x = 0;
119
let y = &raw mut x; //~ mutable pointer

Diff for: ‎tests/ui/consts/const-address-of-mut.stderr

+2-12
Original file line numberDiff line numberDiff line change
@@ -18,18 +18,8 @@ LL | static B: () = { let mut x = 2; &raw mut x; };
1818
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
1919
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
2020

21-
error[E0658]: raw mutable pointers are not allowed in statics
22-
--> $DIR/const-address-of-mut.rs:7:37
23-
|
24-
LL | static mut C: () = { let mut x = 2; &raw mut x; };
25-
| ^^^^^^^^^^
26-
|
27-
= note: see issue #57349 <https://github.com./rust-lang/rust/issues/57349> for more information
28-
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
29-
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
30-
3121
error[E0658]: raw mutable pointers are not allowed in constant functions
32-
--> $DIR/const-address-of-mut.rs:11:13
22+
--> $DIR/const-address-of-mut.rs:9:13
3323
|
3424
LL | let y = &raw mut x;
3525
| ^^^^^^^^^^
@@ -38,6 +28,6 @@ LL | let y = &raw mut x;
3828
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
3929
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date
4030

41-
error: aborting due to 4 previous errors
31+
error: aborting due to 3 previous errors
4232

4333
For more information about this error, try `rustc --explain E0658`.

Diff for: ‎tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr

-10
Original file line numberDiff line numberDiff line change
@@ -133,11 +133,6 @@ help: skipping check for `const_mut_refs` feature
133133
|
134134
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
135135
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
136-
help: skipping check that does not even have a feature gate
137-
--> $DIR/mutable_references_err.rs:40:49
138-
|
139-
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
140-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
141136
help: skipping check that does not even have a feature gate
142137
--> $DIR/mutable_references_err.rs:47:44
143138
|
@@ -148,11 +143,6 @@ help: skipping check that does not even have a feature gate
148143
|
149144
LL | const POINTS_TO_MUTABLE1: &i32 = unsafe { &MUTABLE };
150145
| ^^^^^^^
151-
help: skipping check that does not even have a feature gate
152-
--> $DIR/mutable_references_err.rs:50:36
153-
|
154-
LL | static mut MUTABLE_REF: &mut i32 = &mut 42;
155-
| ^^^^^^^
156146
help: skipping check that does not even have a feature gate
157147
--> $DIR/mutable_references_err.rs:51:45
158148
|

Diff for: ‎tests/ui/consts/static-mut-refs.rs

+24
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,24 @@
1+
// run-pass
2+
#![allow(dead_code)]
3+
4+
// Checks that mutable static items can have mutable slices and other references
5+
6+
7+
static mut TEST: &'static mut [isize] = &mut [1];
8+
static mut EMPTY: &'static mut [isize] = &mut [];
9+
static mut INT: &'static mut isize = &mut 1;
10+
11+
// And the same for raw pointers.
12+
13+
static mut TEST_RAW: *mut [isize] = &mut [1isize] as *mut _;
14+
static mut EMPTY_RAW: *mut [isize] = &mut [] as *mut _;
15+
static mut INT_RAW: *mut isize = &mut 1isize as *mut _;
16+
17+
pub fn main() {
18+
unsafe {
19+
TEST[0] += 1;
20+
assert_eq!(TEST[0], 2);
21+
*INT_RAW += 1;
22+
assert_eq!(*INT_RAW, 2);
23+
}
24+
}

Diff for: ‎tests/ui/consts/static_mut_containing_mut_ref2.rs

+1-1
Original file line numberDiff line numberDiff line change
@@ -7,7 +7,7 @@ static mut STDERR_BUFFER_SPACE: u8 = 0;
77
pub static mut STDERR_BUFFER: () = unsafe {
88
*(&mut STDERR_BUFFER_SPACE) = 42;
99
//[mut_refs]~^ ERROR could not evaluate static initializer
10-
//[stock]~^^ ERROR mutable references are not allowed in statics
10+
//[stock]~^^ ERROR mutation through a reference is not allowed in statics
1111
//[mut_refs]~^^^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
1212
//[stock]~^^^^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
1313
};

Diff for: ‎tests/ui/consts/static_mut_containing_mut_ref2.stock.stderr

+3-3
Original file line numberDiff line numberDiff line change
@@ -13,11 +13,11 @@ help: mutable references are dangerous since if there's any other pointer or ref
1313
LL | *addr_of_mut!(STDERR_BUFFER_SPACE) = 42;
1414
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1515

16-
error[E0658]: mutable references are not allowed in statics
17-
--> $DIR/static_mut_containing_mut_ref2.rs:8:6
16+
error[E0658]: mutation through a reference is not allowed in statics
17+
--> $DIR/static_mut_containing_mut_ref2.rs:8:5
1818
|
1919
LL | *(&mut STDERR_BUFFER_SPACE) = 42;
20-
| ^^^^^^^^^^^^^^^^^^^^^^^^^^
20+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
2121
|
2222
= note: see issue #57349 <https://github.com./rust-lang/rust/issues/57349> for more information
2323
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable

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