Auto merge of #115131 - frank-king:feature/unnamed-fields-lite, r=petrochenkov

Parse unnamed fields and anonymous structs or unions (no-recovery)

It is part of #114782 which implements #49804. Only parse anonymous structs or unions in struct field definition positions.

r? `@petrochenkov`

compiler/rustc_ast/src/ast.rs

@@ -2092,6 +2092,10 @@ pub enum TyKind {
     Never,
     /// A tuple (`(A, B, C, D,...)`).
     Tup(ThinVec<P<Ty>>),
+    /// An anonymous struct type i.e. `struct { foo: Type }`
+    AnonStruct(ThinVec<FieldDef>),
+    /// An anonymous union type i.e. `union { bar: Type }`
+    AnonUnion(ThinVec<FieldDef>),
     /// A path (`module::module::...::Type`), optionally
     /// "qualified", e.g., `<Vec<T> as SomeTrait>::SomeType`.
     ///

compiler/rustc_ast/src/mut_visit.rs

@@ -510,6 +510,9 @@ pub fn noop_visit_ty<T: MutVisitor>(ty: &mut P<Ty>, vis: &mut T) {
             visit_vec(bounds, |bound| vis.visit_param_bound(bound));
         }
         TyKind::MacCall(mac) => vis.visit_mac_call(mac),
+        TyKind::AnonStruct(fields) | TyKind::AnonUnion(fields) => {
+            fields.flat_map_in_place(|field| vis.flat_map_field_def(field));
+        }
     }
     vis.visit_span(span);
     visit_lazy_tts(tokens, vis);

compiler/rustc_ast/src/token.rs

@@ -486,6 +486,8 @@ impl Token {
             Lt | BinOp(Shl)             | // associated path
             ModSep                      => true, // global path
             Interpolated(ref nt) => matches!(**nt, NtTy(..) | NtPath(..)),
+            // For anonymous structs or unions, which only appear in specific positions
+            // (type of struct fields or union fields), we don't consider them as regular types
             _ => false,
         }
     }

compiler/rustc_ast/src/visit.rs

@@ -438,6 +438,9 @@ pub fn walk_ty<'a, V: Visitor<'a>>(visitor: &mut V, typ: &'a Ty) {
         TyKind::Infer | TyKind::ImplicitSelf | TyKind::Err => {}
         TyKind::MacCall(mac) => visitor.visit_mac_call(mac),
         TyKind::Never | TyKind::CVarArgs => {}
+        TyKind::AnonStruct(ref fields, ..) | TyKind::AnonUnion(ref fields, ..) => {
+            walk_list!(visitor, visit_field_def, fields)
+        }
     }
 }