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static mut: allow mutable reference to arbitrary types, not just slices and arrays #117614

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Feb 10, 2024
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static mut: allow mutable reference to arbitrary types, not just slices and arrays #117614

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40 changes: 16 additions & 24 deletions compiler/rustc_const_eval/src/transform/check_consts/check.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -476,35 +476,27 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
}
}

Rvalue::Ref(_, BorrowKind::Mut { .. }, place) => {
let ty = place.ty(self.body, self.tcx).ty;
let is_allowed = match ty.kind() {
// Inside a `static mut`, `&mut [...]` is allowed.
ty::Array(..) | ty::Slice(_)
if self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut) =>
{
true
}

// FIXME(ecstaticmorse): We could allow `&mut []` inside a const context given
// that this is merely a ZST and it is already eligible for promotion.
// This may require an RFC?
/*
ty::Array(_, len) if len.try_eval_target_usize(cx.tcx, cx.param_env) == Some(0)
=> true,
*/
_ => false,
};
Rvalue::Ref(_, BorrowKind::Mut { .. }, place)
| Rvalue::AddressOf(Mutability::Mut, place) => {
// Inside mutable statics, we allow arbitrary mutable references.
// We've allowed `static mut FOO = &mut [elements];` for a long time (the exact
// reasons why are lost to history), and there is no reason to restrict that to
// arrays and slices.
let is_allowed =
self.const_kind() == hir::ConstContext::Static(hir::Mutability::Mut);

if !is_allowed {
self.check_mut_borrow(place.local, hir::BorrowKind::Ref)
self.check_mut_borrow(
place.local,
if matches!(rvalue, Rvalue::Ref(..)) {
hir::BorrowKind::Ref
} else {
hir::BorrowKind::Raw
},
);
}
}

Rvalue::AddressOf(Mutability::Mut, place) => {
self.check_mut_borrow(place.local, hir::BorrowKind::Raw)
}

Rvalue::Ref(_, BorrowKind::Shared | BorrowKind::Fake, place)
| Rvalue::AddressOf(Mutability::Not, place) => {
let borrowed_place_has_mut_interior = qualifs::in_place::<HasMutInterior, _>(
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15 changes: 0 additions & 15 deletions tests/ui/array-slice-vec/check-static-mut-slices.rs
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This file was deleted.

2 changes: 0 additions & 2 deletions tests/ui/consts/const-address-of-mut.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,6 @@ const A: () = { let mut x = 2; &raw mut x; }; //~ mutable pointer

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

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

const fn foo() {
let mut x = 0;
let y = &raw mut x; //~ mutable pointer
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14 changes: 2 additions & 12 deletions tests/ui/consts/const-address-of-mut.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -18,18 +18,8 @@ LL | static B: () = { let mut x = 2; &raw mut x; };
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: raw mutable pointers are not allowed in statics
--> $DIR/const-address-of-mut.rs:7:37
|
LL | static mut C: () = { let mut x = 2; &raw mut x; };
| ^^^^^^^^^^
|
= note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error[E0658]: raw mutable pointers are not allowed in constant functions
--> $DIR/const-address-of-mut.rs:11:13
--> $DIR/const-address-of-mut.rs:9:13
|
LL | let y = &raw mut x;
| ^^^^^^^^^^
Expand All @@ -38,6 +28,6 @@ LL | let y = &raw mut x;
= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable
= note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error: aborting due to 4 previous errors
error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0658`.
10 changes: 0 additions & 10 deletions tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr
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Expand Up @@ -133,11 +133,6 @@ help: skipping check for `const_mut_refs` feature
|
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:40:49
|
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:47:44
|
Expand All @@ -148,11 +143,6 @@ help: skipping check that does not even have a feature gate
|
LL | const POINTS_TO_MUTABLE1: &i32 = unsafe { &MUTABLE };
| ^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:50:36
|
LL | static mut MUTABLE_REF: &mut i32 = &mut 42;
| ^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:51:45
|
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10 changes: 0 additions & 10 deletions tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr
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Original file line number Diff line number Diff line change
Expand Up @@ -133,11 +133,6 @@ help: skipping check for `const_mut_refs` feature
|
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:40:49
|
LL | static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut *(&READONLY as *const _ as *mut _) };
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:47:44
|
Expand All @@ -148,11 +143,6 @@ help: skipping check that does not even have a feature gate
|
LL | const POINTS_TO_MUTABLE1: &i32 = unsafe { &MUTABLE };
| ^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:50:36
|
LL | static mut MUTABLE_REF: &mut i32 = &mut 42;
| ^^^^^^^
help: skipping check that does not even have a feature gate
--> $DIR/mutable_references_err.rs:51:45
|
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24 changes: 24 additions & 0 deletions tests/ui/consts/static-mut-refs.rs
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Original file line number Diff line number Diff line change
@@ -0,0 +1,24 @@
// run-pass
#![allow(dead_code)]

// Checks that mutable static items can have mutable slices and other references


static mut TEST: &'static mut [isize] = &mut [1];
static mut EMPTY: &'static mut [isize] = &mut [];
static mut INT: &'static mut isize = &mut 1;

// And the same for raw pointers.

static mut TEST_RAW: *mut [isize] = &mut [1isize] as *mut _;
static mut EMPTY_RAW: *mut [isize] = &mut [] as *mut _;
static mut INT_RAW: *mut isize = &mut 1isize as *mut _;

pub fn main() {
unsafe {
TEST[0] += 1;
assert_eq!(TEST[0], 2);
*INT_RAW += 1;
assert_eq!(*INT_RAW, 2);
}
}
2 changes: 1 addition & 1 deletion tests/ui/consts/static_mut_containing_mut_ref2.rs
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Expand Up @@ -7,7 +7,7 @@ static mut STDERR_BUFFER_SPACE: u8 = 0;
pub static mut STDERR_BUFFER: () = unsafe {
*(&mut STDERR_BUFFER_SPACE) = 42;
//[mut_refs]~^ ERROR could not evaluate static initializer
//[stock]~^^ ERROR mutable references are not allowed in statics
//[stock]~^^ ERROR mutation through a reference is not allowed in statics
//[mut_refs]~^^^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
//[stock]~^^^^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
};
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6 changes: 3 additions & 3 deletions tests/ui/consts/static_mut_containing_mut_ref2.stock.stderr
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Expand Up @@ -13,11 +13,11 @@ help: mutable references are dangerous since if there's any other pointer or ref
LL | *addr_of_mut!(STDERR_BUFFER_SPACE) = 42;
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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