Improve wording of static_mut_ref

Author: obeis

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;