const_mut_refs: allow mutable refs to statics

11 files changed, 116 insertions, 58 deletions

diff --git a/tests/ui/consts/const-ref-to-static-linux-vtable.rs b/tests/ui/consts/const-ref-to-static-linux-vtable.rs
new file mode 100644
index 00000000000..9325746c1e7
--- /dev/null
+++ b/tests/ui/consts/const-ref-to-static-linux-vtable.rs
@@ -0,0 +1,43 @@
+//@check-pass
+//! This is the reduced version of the "Linux kernel vtable" use-case.
+#![feature(const_mut_refs, const_refs_to_static)]
+use std::ptr::addr_of_mut;
+
+#[repr(C)]
+struct ThisModule(i32);
+
+trait Module {
+    const THIS_MODULE_PTR: *mut ThisModule;
+}
+
+struct MyModule;
+
+// Generated by a macro.
+extern "C" {
+    static mut THIS_MODULE: ThisModule;
+}
+
+// Generated by a macro.
+impl Module for MyModule {
+    const THIS_MODULE_PTR: *mut ThisModule = unsafe { addr_of_mut!(THIS_MODULE) };
+}
+
+struct Vtable {
+    module: *mut ThisModule,
+    foo_fn: fn(*mut ()) -> i32,
+}
+
+trait Foo {
+    type Mod: Module;
+
+    fn foo(&mut self) -> i32;
+}
+
+fn generate_vtable<T: Foo>() -> &'static Vtable {
+    &Vtable {
+        module: T::Mod::THIS_MODULE_PTR,
+        foo_fn: |ptr| unsafe { &mut *ptr.cast::<T>() }.foo(),
+    }
+}
+
+fn main() {}
diff --git a/tests/ui/consts/issue-17718-const-bad-values.rs b/tests/ui/consts/issue-17718-const-bad-values.rs
index 0299bfef1b4..e112a346b65 100644
--- a/tests/ui/consts/issue-17718-const-bad-values.rs
+++ b/tests/ui/consts/issue-17718-const-bad-values.rs
@@ -6,5 +6,6 @@ const C1: &'static mut [usize] = &mut [];
 static mut S: usize = 3;
 const C2: &'static mut usize = unsafe { &mut S };
 //~^ ERROR: referencing statics in constants
+//~| ERROR: mutable references are not allowed
 
 fn main() {}
diff --git a/tests/ui/consts/issue-17718-const-bad-values.stderr b/tests/ui/consts/issue-17718-const-bad-values.stderr
index 57fcb1c7e9a..e755e5601a8 100644
--- a/tests/ui/consts/issue-17718-const-bad-values.stderr
+++ b/tests/ui/consts/issue-17718-const-bad-values.stderr
@@ -16,7 +16,17 @@ LL | const C2: &'static mut usize = unsafe { &mut S };
    = note: `static` and `const` variables can refer to other `const` variables. A `const` variable, however, cannot refer to a `static` variable.
    = help: to fix this, the value can be extracted to a `const` and then used.
 
-error: aborting due to 2 previous errors
+error[E0658]: mutable references are not allowed in constants
+  --> $DIR/issue-17718-const-bad-values.rs:7:41
+   |
+LL | const C2: &'static mut usize = unsafe { &mut S };
+   |                                         ^^^^^^
+   |
+   = 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: aborting due to 3 previous errors
 
 Some errors have detailed explanations: E0658, E0764.
 For more information about an error, try `rustc --explain E0658`.
diff --git a/tests/ui/consts/miri_unleashed/box.stderr b/tests/ui/consts/miri_unleashed/box.stderr
index 5229f1e50cd..a0518c99cda 100644
--- a/tests/ui/consts/miri_unleashed/box.stderr
+++ b/tests/ui/consts/miri_unleashed/box.stderr
@@ -16,7 +16,7 @@ help: skipping check for `const_mut_refs` feature
    |
 LL |     &mut *(Box::new(0))
    |     ^^^^^^^^^^^^^^^^^^^
-help: skipping check that does not even have a feature gate
+help: skipping check for `const_mut_refs` feature
   --> $DIR/box.rs:8:5
    |
 LL |     &mut *(Box::new(0))
diff --git a/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr b/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr
index 401cf46710a..82739c08cf1 100644
--- a/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr
+++ b/tests/ui/consts/miri_unleashed/mutable_references_err.32bit.stderr
@@ -114,7 +114,7 @@ help: skipping check for `const_refs_to_static` feature
    |
 LL | const SUBTLE: &mut i32 = unsafe { &mut FOO };
    |                                        ^^^
-help: skipping check that does not even have a feature gate
+help: skipping check for `const_mut_refs` feature
   --> $DIR/mutable_references_err.rs:32:35
    |
 LL | const SUBTLE: &mut i32 = unsafe { &mut FOO };
diff --git a/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr b/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr
index 0eb01f5b773..844483d88e9 100644
--- a/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr
+++ b/tests/ui/consts/miri_unleashed/mutable_references_err.64bit.stderr
@@ -114,7 +114,7 @@ help: skipping check for `const_refs_to_static` feature
    |
 LL | const SUBTLE: &mut i32 = unsafe { &mut FOO };
    |                                        ^^^
-help: skipping check that does not even have a feature gate
+help: skipping check for `const_mut_refs` feature
   --> $DIR/mutable_references_err.rs:32:35
    |
 LL | const SUBTLE: &mut i32 = unsafe { &mut FOO };
diff --git a/tests/ui/consts/mut-ptr-to-static.rs b/tests/ui/consts/mut-ptr-to-static.rs
new file mode 100644
index 00000000000..d8a788bb37d
--- /dev/null
+++ b/tests/ui/consts/mut-ptr-to-static.rs
@@ -0,0 +1,40 @@
+//@run-pass
+#![feature(const_mut_refs)]
+#![feature(sync_unsafe_cell)]
+
+use std::cell::SyncUnsafeCell;
+use std::ptr;
+
+#[repr(C)]
+struct SyncPtr {
+    foo: *mut u32,
+}
+unsafe impl Sync for SyncPtr {}
+
+static mut STATIC: u32 = 42;
+
+static INTERIOR_MUTABLE_STATIC: SyncUnsafeCell<u32> = SyncUnsafeCell::new(42);
+
+// A static that mutably points to STATIC.
+static PTR: SyncPtr = SyncPtr {
+    foo: unsafe { ptr::addr_of_mut!(STATIC) },
+};
+static INTERIOR_MUTABLE_PTR: SyncPtr = SyncPtr {
+    foo: ptr::addr_of!(INTERIOR_MUTABLE_STATIC) as *mut u32,
+};
+
+fn main() {
+    let ptr = PTR.foo;
+    unsafe {
+        assert_eq!(*ptr, 42);
+        *ptr = 0;
+        assert_eq!(*PTR.foo, 0);
+    }
+
+    let ptr = INTERIOR_MUTABLE_PTR.foo;
+    unsafe {
+        assert_eq!(*ptr, 42);
+        *ptr = 0;
+        assert_eq!(*INTERIOR_MUTABLE_PTR.foo, 0);
+    }
+}
diff --git a/tests/ui/error-codes/E0017.rs b/tests/ui/error-codes/E0017.rs
index 9d3433fa543..c128c2779e2 100644
--- a/tests/ui/error-codes/E0017.rs
+++ b/tests/ui/error-codes/E0017.rs
@@ -1,3 +1,5 @@
+#![feature(const_mut_refs)]
+
 static X: i32 = 1;
 const C: i32 = 2;
 static mut M: i32 = 3;
@@ -5,14 +7,12 @@ static mut M: i32 = 3;
 const CR: &'static mut i32 = &mut C; //~ ERROR mutable references are not allowed
 //~| WARN taking a mutable
 
-static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR E0658
-//~| ERROR cannot borrow
-//~| ERROR mutable references are not allowed
+static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR cannot borrow immutable static item `X` as mutable
 
 static CONST_REF: &'static mut i32 = &mut C; //~ ERROR mutable references are not allowed
 //~| WARN taking a mutable
 
-static STATIC_MUT_REF: &'static mut i32 = unsafe { &mut M }; //~ ERROR mutable references are not
+static STATIC_MUT_REF: &'static mut i32 = unsafe { &mut M };
 //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
 
 fn main() {}
diff --git a/tests/ui/error-codes/E0017.stderr b/tests/ui/error-codes/E0017.stderr
index 2a70f2ee0ae..eb626a7fe3a 100644
--- a/tests/ui/error-codes/E0017.stderr
+++ b/tests/ui/error-codes/E0017.stderr
@@ -14,7 +14,7 @@ LL | static STATIC_MUT_REF: &'static mut i32 = unsafe { addr_of_mut!(M) };
    |                                                    ~~~~~~~~~~~~~~~
 
 warning: taking a mutable reference to a `const` item
-  --> $DIR/E0017.rs:5:30
+  --> $DIR/E0017.rs:7:30
    |
 LL | const CR: &'static mut i32 = &mut C;
    |                              ^^^^^^
@@ -22,36 +22,20 @@ LL | const CR: &'static mut i32 = &mut C;
    = note: each usage of a `const` item creates a new temporary
    = note: the mutable reference will refer to this temporary, not the original `const` item
 note: `const` item defined here
-  --> $DIR/E0017.rs:2:1
+  --> $DIR/E0017.rs:4:1
    |
 LL | const C: i32 = 2;
    | ^^^^^^^^^^^^
    = note: `#[warn(const_item_mutation)]` on by default
 
 error[E0764]: mutable references are not allowed in the final value of constants
-  --> $DIR/E0017.rs:5:30
+  --> $DIR/E0017.rs:7:30
    |
 LL | const CR: &'static mut i32 = &mut C;
    |                              ^^^^^^
 
-error[E0658]: mutation through a reference is not allowed in statics
-  --> $DIR/E0017.rs:8:39
-   |
-LL | static STATIC_REF: &'static mut i32 = &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[E0764]: mutable references are not allowed in the final value of statics
-  --> $DIR/E0017.rs:8:39
-   |
-LL | static STATIC_REF: &'static mut i32 = &mut X;
-   |                                       ^^^^^^
-
 error[E0596]: cannot borrow immutable static item `X` as mutable
-  --> $DIR/E0017.rs:8:39
+  --> $DIR/E0017.rs:10:39
    |
 LL | static STATIC_REF: &'static mut i32 = &mut X;
    |                                       ^^^^^^ cannot borrow as mutable
@@ -65,7 +49,7 @@ LL | static CONST_REF: &'static mut i32 = &mut C;
    = note: each usage of a `const` item creates a new temporary
    = note: the mutable reference will refer to this temporary, not the original `const` item
 note: `const` item defined here
-  --> $DIR/E0017.rs:2:1
+  --> $DIR/E0017.rs:4:1
    |
 LL | const C: i32 = 2;
    | ^^^^^^^^^^^^
@@ -76,13 +60,7 @@ error[E0764]: mutable references are not allowed in the final value of statics
 LL | static CONST_REF: &'static mut i32 = &mut C;
    |                                      ^^^^^^
 
-error[E0764]: mutable references are not allowed in the final value of statics
-  --> $DIR/E0017.rs:15:52
-   |
-LL | static STATIC_MUT_REF: &'static mut i32 = unsafe { &mut M };
-   |                                                    ^^^^^^
-
-error: aborting due to 6 previous errors; 3 warnings emitted
+error: aborting due to 3 previous errors; 3 warnings emitted
 
-Some errors have detailed explanations: E0596, E0658, E0764.
+Some errors have detailed explanations: E0596, E0764.
 For more information about an error, try `rustc --explain E0596`.
diff --git a/tests/ui/error-codes/E0388.rs b/tests/ui/error-codes/E0388.rs
index 6049d95f0d2..bd371328e6b 100644
--- a/tests/ui/error-codes/E0388.rs
+++ b/tests/ui/error-codes/E0388.rs
@@ -3,9 +3,7 @@ const C: i32 = 2;
 
 const CR: &'static mut i32 = &mut C; //~ ERROR mutable references are not allowed
                                      //~| WARN taking a mutable
-static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR cannot borrow
-                                              //~| ERROR E0658
-                                              //~| ERROR mutable references are not allowed
+static STATIC_REF: &'static mut i32 = &mut X; //~ ERROR E0658
 
 static CONST_REF: &'static mut i32 = &mut C; //~ ERROR mutable references are not allowed
                                              //~| WARN taking a mutable
diff --git a/tests/ui/error-codes/E0388.stderr b/tests/ui/error-codes/E0388.stderr
index 1f7b688899e..3e89e3f804b 100644
--- a/tests/ui/error-codes/E0388.stderr
+++ b/tests/ui/error-codes/E0388.stderr
@@ -19,7 +19,7 @@ error[E0764]: mutable references are not allowed in the final value of constants
 LL | const CR: &'static mut i32 = &mut C;
    |                              ^^^^^^
 
-error[E0658]: mutation through a reference is not allowed in statics
+error[E0658]: mutable references are not allowed in statics
   --> $DIR/E0388.rs:6:39
    |
 LL | static STATIC_REF: &'static mut i32 = &mut X;
@@ -29,20 +29,8 @@ LL | static STATIC_REF: &'static mut i32 = &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[E0764]: mutable references are not allowed in the final value of statics
-  --> $DIR/E0388.rs:6:39
-   |
-LL | static STATIC_REF: &'static mut i32 = &mut X;
-   |                                       ^^^^^^
-
-error[E0596]: cannot borrow immutable static item `X` as mutable
-  --> $DIR/E0388.rs:6:39
-   |
-LL | static STATIC_REF: &'static mut i32 = &mut X;
-   |                                       ^^^^^^ cannot borrow as mutable
-
 warning: taking a mutable reference to a `const` item
-  --> $DIR/E0388.rs:10:38
+  --> $DIR/E0388.rs:8:38
    |
 LL | static CONST_REF: &'static mut i32 = &mut C;
    |                                      ^^^^^^
@@ -56,12 +44,12 @@ LL | const C: i32 = 2;
    | ^^^^^^^^^^^^
 
 error[E0764]: mutable references are not allowed in the final value of statics
-  --> $DIR/E0388.rs:10:38
+  --> $DIR/E0388.rs:8:38
    |
 LL | static CONST_REF: &'static mut i32 = &mut C;
    |                                      ^^^^^^
 
-error: aborting due to 5 previous errors; 2 warnings emitted
+error: aborting due to 3 previous errors; 2 warnings emitted
 
-Some errors have detailed explanations: E0596, E0658, E0764.
-For more information about an error, try `rustc --explain E0596`.
+Some errors have detailed explanations: E0658, E0764.
+For more information about an error, try `rustc --explain E0658`.