Improve wording of static_mut_ref

compiler/rustc_error_codes/src/error_codes/E0796.md

@@ -16,7 +16,11 @@ unsafe {
 fn foo<'a>(_x: &'a i32) {}
 ```
 
-Mutable statics can be written to by multiple threads: aliasing violations or
-data races will cause undefined behavior.
+a mutable reference supposedly lives forever, so creating more than one
+is very dangerous and they can accidentally be used in overlapping ways.
 
-Reference of mutable static is a hard error from 2024 edition.
+a shared reference supposedly lives forever, so if there is ever also a
+mutable reference created that is very dangerous as they can accidentally
+be used in overlapping ways.
+
+Reference to mutable static is a hard error in 2024 edition.

compiler/rustc_hir_analysis/messages.ftl

@@ -373,19 +373,21 @@ hir_analysis_start_not_target_feature = `#[start]` function is not allowed to ha
 hir_analysis_start_not_track_caller = `#[start]` function is not allowed to be `#[track_caller]`
     .label = `#[start]` function is not allowed to be `#[track_caller]`
 
-hir_analysis_static_mut_ref = reference of mutable static is disallowed
+hir_analysis_static_mut_ref = reference to mutable static is disallowed
     .label = reference of mutable static
-    .note = mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+    .note = a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+    .note_mut = a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
     .suggestion = shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
     .suggestion_mut = mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
 
-hir_analysis_static_mut_ref_lint = {$shared}reference of mutable static is discouraged
+hir_analysis_static_mut_ref_lint = {$shared}reference to mutable static is discouraged
     .label = shared reference of mutable static
     .label_mut = mutable reference of mutable static
     .suggestion = shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
     .suggestion_mut = mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
-    .note = reference of mutable static is a hard error from 2024 edition
-    .why_note = mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+    .note = reference of mutable static is a hard error in 2024 edition
+    .why_note = a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+    .why_note_mut = a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
 
 hir_analysis_static_specialize = cannot specialize on `'static` lifetime
 

compiler/rustc_hir_analysis/src/check/errs.rs

@@ -71,7 +71,7 @@ fn handle_static_mut_ref(
         } else {
             errors::StaticMutRefSugg::Shared { span, var }
         };
-        tcx.sess.parse_sess.dcx.emit_err(errors::StaticMutRef { span, sugg });
+        tcx.sess.parse_sess.dcx.emit_err(errors::StaticMutRef { span, note_mut: (), sugg });
         return;
     }
 
@@ -92,6 +92,6 @@ fn handle_static_mut_ref(
         STATIC_MUT_REF,
         hir_id,
         span,
-        errors::RefOfMutStatic { shared, why_note: (), label, sugg },
+        errors::RefOfMutStatic { shared, why_note: (), why_note_mut: (), label, sugg },
     );
 }

compiler/rustc_hir_analysis/src/errors.rs

@@ -1459,6 +1459,8 @@ pub struct StaticMutRef {
     #[primary_span]
     #[label]
     pub span: Span,
+    #[note(hir_analysis_note_mut)]
+    pub note_mut: (),
     #[subdiagnostic]
     pub sugg: StaticMutRefSugg,
 }
@@ -1497,6 +1499,8 @@ pub struct RefOfMutStatic<'a> {
     pub shared: &'a str,
     #[note(hir_analysis_why_note)]
     pub why_note: (),
+    #[note(hir_analysis_why_note_mut)]
+    pub why_note_mut: (),
     #[subdiagnostic]
     pub label: RefOfMutStaticLabel,
     #[subdiagnostic]

compiler/rustc_lint_defs/src/builtin.rs

@@ -1807,7 +1807,7 @@ declare_lint! {
     /// Shared or mutable references of mutable static are almost always a mistake and
     /// can lead to undefined behavior and various other problems in your code.
     ///
-    /// This lint is "warn" by default on editions up to 2021, from 2024 there is
+    /// This lint is "warn" by default on editions up to 2021,in 2024 there is
     /// a hard error instead.
     pub STATIC_MUT_REF,
     Warn,

tests/ui/abi/statics/static-mut-foreign.rs

@@ -33,9 +33,9 @@ unsafe fn run() {
     rust_dbg_static_mut = -3;
     assert_eq!(rust_dbg_static_mut, -3);
     static_bound(&rust_dbg_static_mut);
-    //~^ WARN shared reference of mutable static is discouraged [static_mut_ref]
+    //~^ WARN shared reference to mutable static is discouraged [static_mut_ref]
     static_bound_set(&mut rust_dbg_static_mut);
-    //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+    //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
 }
 
 pub fn main() {

tests/ui/abi/statics/static-mut-foreign.stderr

@@ -1,27 +1,29 @@
-warning: shared reference of mutable static is discouraged
+warning: shared reference to mutable static is discouraged
   --> $DIR/static-mut-foreign.rs:35:18
    |
 LL |     static_bound(&rust_dbg_static_mut);
    |                  ^^^^^^^^^^^^^^^^^^^^ shared reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
    |
 LL |     static_bound(addr_of!(rust_dbg_static_mut));
    |                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/static-mut-foreign.rs:37:22
    |
 LL |     static_bound_set(&mut rust_dbg_static_mut);
    |                      ^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |
 LL |     static_bound_set(addr_of_mut!(rust_dbg_static_mut));

tests/ui/borrowck/borrowck-access-permissions.rs

@@ -16,7 +16,7 @@ fn main() {
         let _y1 = &mut static_x; //~ ERROR [E0596]
         unsafe {
             let _y2 = &mut static_x_mut;
-            //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+            //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
         }
     }
 

tests/ui/borrowck/borrowck-access-permissions.stderr

@@ -1,12 +1,13 @@
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/borrowck-access-permissions.rs:18:23
    |
 LL |             let _y2 = &mut static_x_mut;
    |                       ^^^^^^^^^^^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |

tests/ui/borrowck/borrowck-unsafe-static-mutable-borrows.rs

@@ -17,7 +17,7 @@ impl Foo {
 fn main() {
     unsafe {
         let sfoo: *mut Foo = &mut SFOO;
-        //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+        //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
         let x = (*sfoo).x();
         (*sfoo).x[1] += 1;
         *x += 1;

tests/ui/borrowck/borrowck-unsafe-static-mutable-borrows.stderr

@@ -1,12 +1,13 @@
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/borrowck-unsafe-static-mutable-borrows.rs:19:30
    |
 LL |         let sfoo: *mut Foo = &mut SFOO;
    |                              ^^^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |

tests/ui/borrowck/issue-20801.rs

@@ -12,7 +12,7 @@ fn imm_ref() -> &'static T {
 
 fn mut_ref() -> &'static mut T {
     unsafe { &mut GLOBAL_MUT_T }
-    //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+    //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
 }
 
 fn mut_ptr() -> *mut T {

tests/ui/borrowck/issue-20801.stderr

@@ -1,12 +1,13 @@
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/issue-20801.rs:14:14
    |
 LL |     unsafe { &mut GLOBAL_MUT_T }
    |              ^^^^^^^^^^^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |

tests/ui/borrowck/issue-55492-borrowck-migrate-scans-parents.rs

@@ -10,7 +10,7 @@ mod borrowck_closures_unique {
         //~^ ERROR is not declared as mutable
         unsafe {
             c1(&mut Y);
-            //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+            //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
         }
     }
 }
@@ -25,7 +25,7 @@ mod borrowck_closures_unique_grandparent {
         };
         unsafe {
             c1(&mut Z);
-            //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+            //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
         }
     }
 }
@@ -62,7 +62,7 @@ fn main() {
     static mut X: isize = 2;
     unsafe {
         borrowck_closures_unique::e(&mut X);
-        //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+        //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
     }
 
     mutability_errors::capture_assign_whole((1000,));

tests/ui/borrowck/issue-55492-borrowck-migrate-scans-parents.stderr

@@ -1,41 +1,44 @@
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/issue-55492-borrowck-migrate-scans-parents.rs:12:16
    |
 LL |             c1(&mut Y);
    |                ^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |
 LL |             c1(addr_of_mut!(Y));
    |                ~~~~~~~~~~~~~~~
 
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/issue-55492-borrowck-migrate-scans-parents.rs:27:16
    |
 LL |             c1(&mut Z);
    |                ^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |
 LL |             c1(addr_of_mut!(Z));
    |                ~~~~~~~~~~~~~~~
 
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/issue-55492-borrowck-migrate-scans-parents.rs:64:37
    |
 LL |         borrowck_closures_unique::e(&mut X);
    |                                     ^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |
 LL |         borrowck_closures_unique::e(addr_of_mut!(X));

tests/ui/consts/const_let_assign2.rs

@@ -16,7 +16,7 @@ static mut BB: AA = AA::new();
 
 fn main() {
     let ptr = unsafe { &mut BB };
-    //~^ WARN mutable reference of mutable static is discouraged [static_mut_ref]
+    //~^ WARN mutable reference to mutable static is discouraged [static_mut_ref]
     for a in ptr.data.iter() {
         println!("{}", a);
     }

tests/ui/consts/const_let_assign2.stderr

@@ -1,12 +1,13 @@
-warning: mutable reference of mutable static is discouraged
+warning: mutable reference to mutable static is discouraged
   --> $DIR/const_let_assign2.rs:18:24
    |
 LL |     let ptr = unsafe { &mut BB };
    |                        ^^^^^^^ mutable reference of mutable static
    |
    = note: for more information, see issue #114447 <https://github.com/rust-lang/rust/issues/114447>
-   = note: reference of mutable static is a hard error from 2024 edition
-   = note: mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+   = note: reference of mutable static is a hard error in 2024 edition
+   = note: a shared reference supposedly lives forever, so if there is ever also a mutable reference created that is very dangerous as they can accidentally be used in overlapping ways
+   = note: a mutable reference supposedly lives forever, so creating more than one is very dangerous and they can accidentally be used in overlapping ways
    = note: `#[warn(static_mut_ref)]` on by default
 help: mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
    |

tests/ui/consts/const_refs_to_static_fail_invalid.rs

@@ -43,8 +43,8 @@ fn mutable() {
     // This *must not build*, the constant we are matching against
     // could change its value!
     match &42 {
-        C => {}, //~ERROR: could not evaluate constant pattern
-        _ => {},
+        C => {} //~ERROR: could not evaluate constant pattern
+        _ => {}
     }
 }
 

tests/ui/consts/const_refs_to_static_fail_invalid.stderr

@@ -46,7 +46,7 @@ LL |     const C: &i32 = unsafe { &S_MUT };
 error: could not evaluate constant pattern
   --> $DIR/const_refs_to_static_fail_invalid.rs:46:9
    |
-LL |         C => {},
+LL |         C => {}
    |         ^
 
 error: aborting due to 6 previous errors