Reorder extern static errors over static mut

Extern statics are much more spicy than static mut: they may be uninit!
Issue their errors first, and in doing so make miri happier.

Author: workingjubilee

compiler/rustc_mir_build/src/check_unsafety.rs

@@ -464,12 +464,13 @@ impl<'a, 'tcx> Visitor<'a, 'tcx> for UnsafetyVisitor<'a, 'tcx> {
                 if let ExprKind::StaticRef { def_id, .. } | ExprKind::ThreadLocalRef(def_id) =
                     self.thir[arg].kind
                 {
-                    if self.tcx.is_mutable_static(def_id) && allow_implicit_static_deref {
+                    // The requirements for an extern static are much more stringent
+                    if self.tcx.is_foreign_item(def_id) {
+                        self.requires_unsafe(expr.span, UseOfExternStatic);
+                    } else if self.tcx.is_mutable_static(def_id) && allow_implicit_static_deref {
                         // we're only taking the address of the implicit place expr, it's fine
                     } else if self.tcx.is_mutable_static(def_id) {
                         self.requires_unsafe(expr.span, UseOfMutableStatic);
-                    } else if self.tcx.is_foreign_item(def_id) {
-                        self.requires_unsafe(expr.span, UseOfExternStatic);
                     }
                 } else if self.thir[arg].ty.is_unsafe_ptr() {
                     self.requires_unsafe(expr.span, DerefOfRawPointer);

src/tools/miri/tests/pass/static_mut.rs

@@ -2,7 +2,7 @@ use std::ptr::addr_of;
 
 static mut FOO: i32 = 42;
 
-static BAR: Foo = Foo(unsafe { addr_of!(FOO) });
+static BAR: Foo = Foo(addr_of!(FOO));
 
 #[allow(dead_code)]
 struct Foo(*const i32);

tests/ui/static/safe-extern-statics-mut.rs

@@ -8,10 +8,10 @@ extern "C" {
 }
 
 fn main() {
-    let b = B; //~ ERROR use of mutable static is unsafe
-    let rb = &B; //~ ERROR use of mutable static is unsafe
-    //~^ WARN shared reference to mutable static is discouraged [static_mut_refs]
-    let xb = XB; //~ ERROR use of mutable static is unsafe
-    let xrb = &XB; //~ ERROR use of mutable static is unsafe
-    //~^ WARN shared reference to mutable static is discouraged [static_mut_refs]
+    let b = B; //~ static is unsafe
+    let rb = &B; //~ static is unsafe
+                 //~^ WARN shared reference to mutable static is discouraged [static_mut_refs]
+    let xb = XB; //~ static is unsafe
+    let xrb = &XB; //~ static is unsafe
+                   //~^ WARN shared reference to mutable static is discouraged [static_mut_refs]
 }

tests/ui/static/safe-extern-statics-mut.stderr

@@ -27,37 +27,37 @@ help: use `addr_of!` instead to create a raw pointer
 LL |     let xrb = addr_of!(XB);
    |               ~~~~~~~~~~~~
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/safe-extern-statics-mut.rs:11:13
    |
 LL |     let b = B;
-   |             ^ use of mutable static
+   |             ^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/safe-extern-statics-mut.rs:12:15
    |
 LL |     let rb = &B;
-   |               ^ use of mutable static
+   |               ^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/safe-extern-statics-mut.rs:14:14
    |
 LL |     let xb = XB;
-   |              ^^ use of mutable static
+   |              ^^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/safe-extern-statics-mut.rs:15:16
    |
 LL |     let xrb = &XB;
-   |                ^^ use of mutable static
+   |                ^^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
 error: aborting due to 4 previous errors; 2 warnings emitted
 

tests/ui/static/static-mut-foreign-requires-unsafe.stderr

@@ -1,26 +1,26 @@
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/static-mut-foreign-requires-unsafe.rs:6:5
    |
 LL |     a += 3;
-   |     ^ use of mutable static
+   |     ^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/static-mut-foreign-requires-unsafe.rs:7:5
    |
 LL |     a = 4;
-   |     ^ use of mutable static
+   |     ^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
-error[E0133]: use of mutable static is unsafe and requires unsafe function or block
+error[E0133]: use of extern static is unsafe and requires unsafe function or block
   --> $DIR/static-mut-foreign-requires-unsafe.rs:8:14
    |
 LL |     let _b = a;
-   |              ^ use of mutable static
+   |              ^ use of extern static
    |
-   = note: mutable statics can be mutated by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: extern statics are not controlled by the Rust type system: invalid data, aliasing violations or data races will cause undefined behavior
 
 error: aborting due to 3 previous errors