Auto merge of rust-lang#121158 - GuillaumeGomez:rollup-l38pzjw, r=GuillaumeGomez

Rollup of 13 pull requests

Successful merges:

 - rust-lang#118264 (Optimize `VecDeque::drain` for (half-)open ranges)
 - rust-lang#120741 (Make `io::BorrowedCursor::advance` safe)
 - rust-lang#120777 (Bump Unicode to version 15.1.0, regenerate tables)
 - rust-lang#120971 (Fix comment in core/src/str/validations.rs)
 - rust-lang#121034 (Improve wording of `static_mut_ref`)
 - rust-lang#121095 (Add extra indent spaces for rust-playground link)
 - rust-lang#121109 (Add an ErrorGuaranteed to ast::TyKind::Err (attempt 2))
 - rust-lang#121119 (Make `async Fn` trait kind errors better)
 - rust-lang#121141 (Fix closure kind docs)
 - rust-lang#121145 (Update aarch64 target feature docs to match LLVM)
 - rust-lang#121146 (Only point out non-diverging arms for match suggestions)
 - rust-lang#121147 (Avoid debug logging entire MIR body)
 - rust-lang#121155 (doc: add note about panicking examples for strict_overflow_ops)

r? `@ghost`
`@rustbot` modify labels: rollup

Author: bors

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]>> {