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

RalfJung · RalfJung · commit 9a819ab8f7f6 · 2024-01-28T10:00:23.000+01:00
diff --git a/compiler/rustc_const_eval/src/transform/check_consts/check.rs b/compiler/rustc_const_eval/src/transform/check_consts/check.rs
@@ -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, _>(
diff --git a/tests/ui/array-slice-vec/check-static-mut-slices.rs b/tests/ui/array-slice-vec/check-static-mut-slices.rs
diff --git a/tests/ui/consts/const-address-of-mut.rs b/tests/ui/consts/const-address-of-mut.rs
@@ -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
diff --git a/tests/ui/consts/const-address-of-mut.stderr b/tests/ui/consts/const-address-of-mut.stderr
@@ -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;
    |             ^^^^^^^^^^
@@ -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`.
diff --git a/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr b/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr
@@ -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
    |
@@ -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
    |
diff --git a/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr b/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr
@@ -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
    |
@@ -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
    |
diff --git a/tests/ui/consts/static-mut-refs.rs b/tests/ui/consts/static-mut-refs.rs
@@ -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);
+    }
+}
diff --git a/tests/ui/consts/static_mut_containing_mut_ref2.rs b/tests/ui/consts/static_mut_containing_mut_ref2.rs
@@ -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]
 };
diff --git a/tests/ui/consts/static_mut_containing_mut_ref2.stock.stderr b/tests/ui/consts/static_mut_containing_mut_ref2.stock.stderr
@@ -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

Original file line number	Diff line number	Diff line change
@@ -133,11 +133,6 @@ help: skipping check for `const_mut_refs` feature
`133`	`133`	`\|`
`134`	`134`	`LL \| static mut MUT_TO_READONLY: &mut i32 = unsafe { &mut (&READONLY as const _ as *mut _) };`
`135`	`135`	`\| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^`
`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`		`- \| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^`
`141`	`136`	`help: skipping check that does not even have a feature gate`
`142`	`137`	`--> $DIR/mutable_references_err.rs:47:44`
`143`	`138`	`\|`
`@@ -148,11 +143,6 @@ help: skipping check that does not even have a feature gate`
`148`	`143`	`\|`
`149`	`144`	`LL \| const POINTS_TO_MUTABLE1: &i32 = unsafe { &MUTABLE };`
`150`	`145`	`\| ^^^^^^^`
`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`		`- \| ^^^^^^^`
`156`	`146`	`help: skipping check that does not even have a feature gate`
`157`	`147`	`--> $DIR/mutable_references_err.rs:51:45`
`158`	`148`	`\|`
Original file line number	Diff line number	Diff line change
`@@ -13,11 +13,11 @@ help: mutable references are dangerous since if there's any other pointer or ref`
`13`	`13`	`LL \| *addr_of_mut!(STDERR_BUFFER_SPACE) = 42;`
`14`	`14`	`\| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~`
`15`	`15`
`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`
`18`	`18`	`\|`
`19`	`19`	`LL \| *(&mut STDERR_BUFFER_SPACE) = 42;`
`20`		`- \| ^^^^^^^^^^^^^^^^^^^^^^^^^^`
	`20`	`+ \| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^`
`21`	`21`	`\|`
`22`	`22`	`= note: see issue #57349 <https://github.com/rust-lang/rust/issues/57349> for more information`
`23`	`23`	= help: add `#![feature(const_mut_refs)]` to the crate attributes to enable