Rollup of 13 pull requests

compiler/rustc_ast/src/ast.rs

@@ -2136,10 +2136,12 @@ pub enum TyKind {
     ImplicitSelf,
     /// A macro in the type position.
     MacCall(P<MacCall>),
-    /// Placeholder for a kind that has failed to be defined.
-    Err,
     /// Placeholder for a `va_list`.
     CVarArgs,
+    /// Sometimes we need a dummy value when no error has occurred.
+    Dummy,
+    /// Placeholder for a kind that has failed to be defined.
+    Err(ErrorGuaranteed),
 }
 
 impl TyKind {

compiler/rustc_ast/src/mut_visit.rs

@@ -481,7 +481,12 @@ pub fn noop_visit_ty<T: MutVisitor>(ty: &mut P<Ty>, vis: &mut T) {
     let Ty { id, kind, span, tokens } = ty.deref_mut();
     vis.visit_id(id);
     match kind {
-        TyKind::Infer | TyKind::ImplicitSelf | TyKind::Err | TyKind::Never | TyKind::CVarArgs => {}
+        TyKind::Infer
+        | TyKind::ImplicitSelf
+        | TyKind::Err(_)
+        | TyKind::Dummy
+        | TyKind::Never
+        | TyKind::CVarArgs => {}
         TyKind::Slice(ty) => vis.visit_ty(ty),
         TyKind::Ptr(mt) => vis.visit_mt(mt),
         TyKind::Ref(lt, mt) => {
@@ -1649,7 +1654,7 @@ impl DummyAstNode for Ty {
     fn dummy() -> Self {
         Ty {
             id: DUMMY_NODE_ID,
-            kind: TyKind::Err,
+            kind: TyKind::Dummy,
             span: Default::default(),
             tokens: Default::default(),
         }

compiler/rustc_ast/src/visit.rs

@@ -447,7 +447,7 @@ pub fn walk_ty<'a, V: Visitor<'a>>(visitor: &mut V, typ: &'a Ty) {
             walk_list!(visitor, visit_param_bound, bounds, BoundKind::Impl);
         }
         TyKind::Typeof(expression) => visitor.visit_anon_const(expression),
-        TyKind::Infer | TyKind::ImplicitSelf | TyKind::Err => {}
+        TyKind::Infer | TyKind::ImplicitSelf | TyKind::Dummy | TyKind::Err(_) => {}
         TyKind::MacCall(mac) => visitor.visit_mac_call(mac),
         TyKind::Never | TyKind::CVarArgs => {}
         TyKind::AnonStruct(_, ref fields) | TyKind::AnonUnion(_, ref fields) => {

compiler/rustc_ast_lowering/src/lib.rs

@@ -1286,7 +1286,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     fn lower_ty_direct(&mut self, t: &Ty, itctx: ImplTraitContext) -> hir::Ty<'hir> {
         let kind = match &t.kind {
             TyKind::Infer => hir::TyKind::Infer,
-            TyKind::Err => hir::TyKind::Err(self.dcx().has_errors().unwrap()),
+            TyKind::Err(guar) => hir::TyKind::Err(*guar),
             // Lower the anonymous structs or unions in a nested lowering context.
             //
             // ```
@@ -1504,6 +1504,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 );
                 hir::TyKind::Err(guar)
             }
+            TyKind::Dummy => panic!("`TyKind::Dummy` should never be lowered"),
         };
 
         hir::Ty { kind, span: self.lower_span(t.span), hir_id: self.lower_node_id(t.id) }

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -881,7 +881,8 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                         &item.vis,
                         errors::VisibilityNotPermittedNote::TraitImpl,
                     );
-                    if let TyKind::Err = self_ty.kind {
+                    // njn: use Dummy here
+                    if let TyKind::Err(_) = self_ty.kind {
                         this.dcx().emit_err(errors::ObsoleteAuto { span: item.span });
                     }
                     if let (&Unsafe::Yes(span), &ImplPolarity::Negative(sp)) = (unsafety, polarity)

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1048,11 +1048,16 @@ impl<'a> State<'a> {
             ast::TyKind::Infer => {
                 self.word("_");
             }
-            ast::TyKind::Err => {
+            ast::TyKind::Err(_) => {
                 self.popen();
                 self.word("/*ERROR*/");
                 self.pclose();
             }
+            ast::TyKind::Dummy => {
+                self.popen();
+                self.word("/*DUMMY*/");
+                self.pclose();
+            }
             ast::TyKind::ImplicitSelf => {
                 self.word("Self");
             }

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_expand/src/base.rs

@@ -567,10 +567,13 @@ impl DummyResult {
     }
 
     /// A plain dummy type.
-    pub fn raw_ty(sp: Span, is_error: bool) -> P<ast::Ty> {
+    pub fn raw_ty(sp: Span) -> P<ast::Ty> {
+        // FIXME(nnethercote): you might expect `ast::TyKind::Dummy` to be used here, but some
+        // values produced here end up being lowered to HIR, which `ast::TyKind::Dummy` does not
+        // support, so we use an empty tuple instead.
         P(ast::Ty {
             id: ast::DUMMY_NODE_ID,
-            kind: if is_error { ast::TyKind::Err } else { ast::TyKind::Tup(ThinVec::new()) },
+            kind: ast::TyKind::Tup(ThinVec::new()),
             span: sp,
             tokens: None,
         })
@@ -611,7 +614,7 @@ impl MacResult for DummyResult {
     }
 
     fn make_ty(self: Box<DummyResult>) -> Option<P<ast::Ty>> {
-        Some(DummyResult::raw_ty(self.span, self.is_error))
+        Some(DummyResult::raw_ty(self.span))
     }
 
     fn make_arms(self: Box<DummyResult>) -> Option<SmallVec<[ast::Arm; 1]>> {

compiler/rustc_hir_analysis/messages.ftl

@@ -373,19 +373,24 @@ 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

@@ -1455,12 +1455,13 @@ 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)]
@@ -1491,30 +1492,15 @@ 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_hir_typeck/src/_match.rs

@@ -79,7 +79,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             CoerceMany::with_coercion_sites(coerce_first, arms)
         };
 
-        let mut other_arms = vec![]; // Used only for diagnostics.
+        let mut prior_non_diverging_arms = vec![]; // Used only for diagnostics.
         let mut prior_arm = None;
         for arm in arms {
             if let Some(e) = &arm.guard {
@@ -118,9 +118,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         prior_arm_ty,
                         prior_arm_span,
                         scrut_span: scrut.span,
-                        scrut_hir_id: scrut.hir_id,
                         source: match_src,
-                        prior_arms: other_arms.clone(),
+                        prior_non_diverging_arms: prior_non_diverging_arms.clone(),
                         opt_suggest_box_span,
                     })),
                 ),
@@ -142,16 +141,16 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 false,
             );
 
-            other_arms.push(arm_span);
-            if other_arms.len() > 5 {
-                other_arms.remove(0);
-            }
-
             if !arm_ty.is_never() {
                 // When a match arm has type `!`, then it doesn't influence the expected type for
                 // the following arm. If all of the prior arms are `!`, then the influence comes
                 // from elsewhere and we shouldn't point to any previous arm.
                 prior_arm = Some((arm_block_id, arm_ty, arm_span));
+
+                prior_non_diverging_arms.push(arm_span);
+                if prior_non_diverging_arms.len() > 5 {
+                    prior_non_diverging_arms.remove(0);
+                }
             }
         }