Auto merge of rust-lang#121034 - obeis:improve-static-mut-ref, r=RalfJung

Improve wording of `static_mut_ref`

Close rust-lang#120964

Author: bors

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 statics are a hard error in the 2024 edition.

compiler/rustc_hir_analysis/messages.ftl

@@ -375,19 +375,24 @@ 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
-    .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 = {$shared}reference of mutable static is discouraged
-    .label = shared reference of mutable static
-    .label_mut = mutable reference of mutable static
-    .suggestion = shared references are dangerous since if there's any kind of mutation of that static while the reference lives, that's UB; use `addr_of!` instead to create a raw pointer
-    .suggestion_mut = mutable references are dangerous since if there's any other pointer or reference used for that static while the reference lives, that's UB; use `addr_of_mut!` instead to create a raw pointer
-    .note = reference of mutable static is a hard error from 2024 edition
-    .why_note = mutable statics can be written to by multiple threads: aliasing violations or data races will cause undefined behavior
+hir_analysis_static_mut_ref = creating a {$shared} reference to a mutable static
+    .label = {$shared} reference to mutable static
+    .note = {$shared ->
+        [shared] 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
+        *[mutable] 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 = use `addr_of!` instead to create a raw pointer
+    .suggestion_mut = use `addr_of_mut!` instead to create a raw pointer
+
+hir_analysis_static_mut_refs_lint = creating a {$shared} reference to mutable static is discouraged
+    .label = {$shared} reference to mutable static
+    .suggestion = use `addr_of!` instead to create a raw pointer
+    .suggestion_mut = use `addr_of_mut!` instead to create a raw pointer
+    .note = this will be a hard error in the 2024 edition
+    .why_note = {$shared ->
+        [shared] 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
+        *[mutable] 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

@@ -1462,12 +1462,13 @@ pub struct OnlyCurrentTraitsPointerSugg<'a> {
 #[derive(Diagnostic)]
 #[diag(hir_analysis_static_mut_ref, code = E0796)]
 #[note]
-pub struct StaticMutRef {
+pub struct StaticMutRef<'a> {
     #[primary_span]
     #[label]
     pub span: Span,
     #[subdiagnostic]
     pub sugg: StaticMutRefSugg,
+    pub shared: &'a str,
 }
 
 #[derive(Subdiagnostic)]
@@ -1498,30 +1499,15 @@ 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)]
 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

@@ -325,6 +325,7 @@ 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 +261,9 @@ 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
+#[cfg_attr(bootstrap, allow(static_mut_ref))]
+#[cfg_attr(not(bootstrap), allow(static_mut_refs))]
 pub unsafe fn panic(data: Box<dyn Any + Send>) -> u32 {
     use core::intrinsics::atomic_store_seqcst;
 
@@ -324,8 +325,9 @@ 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
+#[cfg_attr(bootstrap, allow(static_mut_ref))]
+#[cfg_attr(not(bootstrap), 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};