Improve wording of static_mut_ref

Rename `static_mut_ref` lint to `static_mut_refs`

Author: obeis

compiler/rustc_codegen_cranelift/example/mini_core_hello_world.rs

@@ -112,8 +112,8 @@ fn start<T: Termination + 'static>(
 
 static mut NUM: u8 = 6 * 7;
 
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[allow(static_mut_refs)]
 static NUM_REF: &'static u8 = unsafe { &NUM };
 
 unsafe fn zeroed<T>() -> T {

compiler/rustc_codegen_gcc/example/mini_core_hello_world.rs

@@ -99,8 +99,8 @@ fn start<T: Termination + 'static>(
 
 static mut NUM: u8 = 6 * 7;
 
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[allow(static_mut_refs)]
 static NUM_REF: &'static u8 = unsafe { &NUM };
 
 macro_rules! assert {

compiler/rustc_error_codes/src/error_codes/E0796.md

@@ -1,22 +1,26 @@
-Reference of mutable static.
+You have created a reference to a mutable static.
 
 Erroneous code example:
 
 ```compile_fail,edition2024,E0796
 static mut X: i32 = 23;
-static mut Y: i32 = 24;
 
-unsafe {
-  let y = &X;
-  let ref x = X;
-  let (x, y) = (&X, &Y);
-  foo(&X);
+fn work() {
+  let _val = unsafe { X };
 }
 
-fn foo<'a>(_x: &'a i32) {}
+let x_ref = unsafe { &mut X };
+work();
+// The next line has Undefined Behavior!
+// `x_ref` is a mutable reference and allows no aliases,
+// but `work` has been reading the reference between
+// the moment `x_ref` was created and when it was used.
+// This violates the uniqueness of `x_ref`.
+*x_ref = 42;
 ```
 
-Mutable statics can be written to by multiple threads: aliasing violations or
-data races will cause undefined behavior.
+A reference to a mutable static has lifetime `'static`. This is very dangerous
+as it is easy to accidentally overlap the lifetime of that reference with
+other, conflicting accesses to the same static.
 
-Reference of mutable static is a hard error from 2024 edition.
+References to mutable static are a hard error in the 2024 edition.

compiler/rustc_hir_analysis/messages.ftl

@@ -373,19 +373,20 @@ 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
-    .label = reference of mutable static
-    .note = mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+hir_analysis_static_mut_ref = creating a {$shared}reference to a mutable static
+    .label = {$shared}reference to mutable static
+    .note = this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
+    .note_mut = this mutable reference has lifetime `'static`, but if the static gets accessed (read or written) by any other means, or any other reference is created, then any further use of this mutable reference is Undefined Behavior
     .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 = {$shared}reference of mutable static is discouraged
-    .label = shared reference of mutable static
-    .label_mut = mutable reference of mutable static
+hir_analysis_static_mut_refs_lint = {$shared}reference to mutable static is discouraged
+    .label = {$shared}reference to 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 = this will be a hard error in the 2024 edition
+    .why_note = this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
+    .why_note_mut = this mutable reference has lifetime `'static`, but if the static gets accessed (read or written) by any other means, or any other reference is created, then any further use of this mutable reference is Undefined Behavior
 
 hir_analysis_static_specialize = cannot specialize on `'static` lifetime
 

compiler/rustc_hir_analysis/src/check/errs.rs

@@ -1,6 +1,6 @@
 use rustc_hir as hir;
 use rustc_hir_pretty::qpath_to_string;
-use rustc_lint_defs::builtin::STATIC_MUT_REF;
+use rustc_lint_defs::builtin::STATIC_MUT_REFS;
 use rustc_middle::ty::TyCtxt;
 use rustc_span::Span;
 use rustc_type_ir::Mutability;
@@ -66,32 +66,24 @@ fn handle_static_mut_ref(
     hir_id: hir::HirId,
 ) {
     if e2024 {
-        let sugg = if mutable {
-            errors::StaticMutRefSugg::Mut { span, var }
+        let (sugg, shared) = if mutable {
+            (errors::StaticMutRefSugg::Mut { span, var }, "mutable ")
         } else {
-            errors::StaticMutRefSugg::Shared { span, var }
+            (errors::StaticMutRefSugg::Shared { span, var }, "shared ")
         };
-        tcx.sess.parse_sess.dcx.emit_err(errors::StaticMutRef { span, sugg });
+        tcx.sess.parse_sess.dcx.emit_err(errors::StaticMutRef { span, sugg, shared });
         return;
     }
 
-    let (label, sugg, shared) = if mutable {
-        (
-            errors::RefOfMutStaticLabel::Mut { span },
-            errors::RefOfMutStaticSugg::Mut { span, var },
-            "mutable ",
-        )
+    let (sugg, shared) = if mutable {
+        (errors::RefOfMutStaticSugg::Mut { span, var }, "mutable ")
     } else {
-        (
-            errors::RefOfMutStaticLabel::Shared { span },
-            errors::RefOfMutStaticSugg::Shared { span, var },
-            "shared ",
-        )
+        (errors::RefOfMutStaticSugg::Shared { span, var }, "shared ")
     };
     tcx.emit_node_span_lint(
-        STATIC_MUT_REF,
+        STATIC_MUT_REFS,
         hir_id,
         span,
-        errors::RefOfMutStatic { shared, why_note: (), label, sugg },
+        errors::RefOfMutStatic { span, sugg, shared },
     );
 }

compiler/rustc_hir_analysis/src/errors.rs

@@ -1455,12 +1455,14 @@ pub struct OnlyCurrentTraitsPointerSugg<'a> {
 #[derive(Diagnostic)]
 #[diag(hir_analysis_static_mut_ref, code = E0796)]
 #[note]
-pub struct StaticMutRef {
+#[note(hir_analysis_note_mut)]
+pub struct StaticMutRef<'a> {
     #[primary_span]
     #[label]
     pub span: Span,
     #[subdiagnostic]
     pub sugg: StaticMutRefSugg,
+    pub shared: &'a str,
 }
 
 #[derive(Subdiagnostic)]
@@ -1491,30 +1493,16 @@ pub enum StaticMutRefSugg {
 
 // STATIC_MUT_REF lint
 #[derive(LintDiagnostic)]
-#[diag(hir_analysis_static_mut_ref_lint)]
+#[diag(hir_analysis_static_mut_refs_lint)]
 #[note]
+#[note(hir_analysis_why_note)]
+#[note(hir_analysis_why_note_mut)]
 pub struct RefOfMutStatic<'a> {
-    pub shared: &'a str,
-    #[note(hir_analysis_why_note)]
-    pub why_note: (),
-    #[subdiagnostic]
-    pub label: RefOfMutStaticLabel,
+    #[label]
+    pub span: Span,
     #[subdiagnostic]
     pub sugg: RefOfMutStaticSugg,
-}
-
-#[derive(Subdiagnostic)]
-pub enum RefOfMutStaticLabel {
-    #[label(hir_analysis_label)]
-    Shared {
-        #[primary_span]
-        span: Span,
-    },
-    #[label(hir_analysis_label_mut)]
-    Mut {
-        #[primary_span]
-        span: Span,
-    },
+    pub shared: &'a str,
 }
 
 #[derive(Subdiagnostic)]

compiler/rustc_lint/src/lib.rs

@@ -324,6 +324,7 @@ fn register_builtins(store: &mut LintStore) {
     store.register_renamed("or_patterns_back_compat", "rust_2021_incompatible_or_patterns");
     store.register_renamed("non_fmt_panic", "non_fmt_panics");
     store.register_renamed("unused_tuple_struct_fields", "dead_code");
+    store.register_renamed("static_mut_ref", "static_mut_refs");
 
     // These were moved to tool lints, but rustc still sees them when compiling normally, before
     // tool lints are registered, so `check_tool_name_for_backwards_compat` doesn't work. Use

compiler/rustc_lint_defs/src/builtin.rs

@@ -89,7 +89,7 @@ declare_lint_pass! {
         SINGLE_USE_LIFETIMES,
         SOFT_UNSTABLE,
         STABLE_FEATURES,
-        STATIC_MUT_REF,
+        STATIC_MUT_REFS,
         SUSPICIOUS_AUTO_TRAIT_IMPLS,
         TEST_UNSTABLE_LINT,
         TEXT_DIRECTION_CODEPOINT_IN_COMMENT,
@@ -1769,7 +1769,7 @@ declare_lint! {
 }
 
 declare_lint! {
-    /// The `static_mut_ref` lint checks for shared or mutable references
+    /// The `static_mut_refs` lint checks for shared or mutable references
     /// of mutable static inside `unsafe` blocks and `unsafe` functions.
     ///
     /// ### Example
@@ -1807,9 +1807,9 @@ 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,
+    pub STATIC_MUT_REFS,
     Warn,
     "shared references or mutable references of mutable static is discouraged",
     @future_incompatible = FutureIncompatibleInfo {

library/panic_unwind/src/seh.rs

@@ -261,8 +261,8 @@ cfg_if::cfg_if! {
    }
 }
 
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[allow(static_mut_refs)]
 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     use core::intrinsics::atomic_store_seqcst;
 
@@ -324,8 +324,8 @@ pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     _CxxThrowException(throw_ptr, &mut THROW_INFO as *mut _ as *mut _);
 }
 
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[allow(static_mut_refs)]
 pub unsafe fn cleanup(payload: *mut u8) -> Box<dyn Any + Send> {
     // A null payload here means that we got here from the catch (...) of
     // __rust_try. This happens when a non-Rust foreign exception is caught.

library/std/src/panicking.rs

@@ -337,8 +337,9 @@ pub mod panic_count {
 #[doc(hidden)]
 #[cfg(not(feature = "panic_immediate_abort"))]
 #[unstable(feature = "update_panic_count", issue = "none")]
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[cfg_attr(bootstrap, allow(static_mut_ref))]
+#[cfg_attr(not(bootstrap), allow(static_mut_refs))]
 pub mod panic_count {
     use crate::cell::Cell;
     use crate::sync::atomic::{AtomicUsize, Ordering};

library/std/src/sys/pal/common/thread_local/fast_local.rs

@@ -13,8 +13,9 @@ pub macro thread_local_inner {
     (@key $t:ty, const $init:expr) => {{
         #[inline]
         #[deny(unsafe_op_in_unsafe_fn)]
-        // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-        #[allow(static_mut_ref)]
+        // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+        #[cfg_attr(bootstrap, allow(static_mut_ref))]
+        #[cfg_attr(not(bootstrap), allow(static_mut_refs))]
         unsafe fn __getit(
             _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
         ) -> $crate::option::Option<&'static $t> {

library/std/src/sys/pal/common/thread_local/static_local.rs

@@ -11,8 +11,8 @@ pub macro thread_local_inner {
     (@key $t:ty, const $init:expr) => {{
         #[inline] // see comments below
         #[deny(unsafe_op_in_unsafe_fn)]
-        // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-        #[allow(static_mut_ref)]
+        // FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+        #[allow(static_mut_refs)]
         unsafe fn __getit(
             _init: $crate::option::Option<&mut $crate::option::Option<$t>>,
         ) -> $crate::option::Option<&'static $t> {

library/std/src/thread/local.rs

@@ -180,8 +180,8 @@ impl<T: 'static> fmt::Debug for LocalKey<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "thread_local_macro")]
 #[allow_internal_unstable(thread_local_internals)]
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[cfg_attr(not(bootstrap), allow(static_mut_refs))]
 macro_rules! thread_local {
     // empty (base case for the recursion)
     () => {};

src/tools/miri/tests/fail/tls/tls_static_dealloc.rs

@@ -1,8 +1,8 @@
 //! Ensure that thread-local statics get deallocated when the thread dies.
 
 #![feature(thread_local)]
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#![allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#![allow(static_mut_refs)]
 
 #[thread_local]
 static mut TLS: u8 = 0;

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

@@ -1,7 +1,7 @@
 static mut FOO: i32 = 42;
 
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#[allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#[allow(static_mut_refs)]
 static BAR: Foo = Foo(unsafe { &FOO as *const _ });
 
 #[allow(dead_code)]

src/tools/miri/tests/pass/tls/tls_static.rs

@@ -8,8 +8,8 @@
 //! test, we also check that thread-locals act as per-thread statics.
 
 #![feature(thread_local)]
-// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_ref` lint
-#![allow(static_mut_ref)]
+// FIXME: Use `SyncUnsafeCell` instead of allowing `static_mut_refs` lint
+#![allow(static_mut_refs)]
 
 use std::thread;
 

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_refs]
     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_refs]
 }
 
 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
+   |                  ^^^^^^^^^^^^^^^^^^^^ shared reference to 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: `#[warn(static_mut_ref)]` on by default
+   = note: this will be a hard error in the 2024 edition
+   = note: this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
+   = note: this mutable reference has lifetime `'static`, but if the static gets accessed (read or written) by any other means, or any other reference is created, then any further use of this mutable reference is Undefined Behavior
+   = note: `#[warn(static_mut_refs)]` 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
+   |                      ^^^^^^^^^^^^^^^^^^^^^^^^ mutable reference to 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: this will be a hard error in the 2024 edition
+   = note: this shared reference has lifetime `'static`, but if the static ever gets mutated, or a mutable reference is created, then any further use of this shared reference is Undefined Behavior
+   = note: this mutable reference has lifetime `'static`, but if the static gets accessed (read or written) by any other means, or any other reference is created, then any further use of this mutable reference is Undefined Behavior
 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_refs]
         }
     }