Revert "Implement Anonymous{Struct, Union} in the AST"

This reverts commit 059b68d.

Note that this was manually adjusted to retain some of the refactoring
introduced by commit 059b68d, so that it could
likewise retain the correction introduced in commit
5b4bc05

(cherry picked from commit 91feb76)

Author: pnkfelix

compiler/rustc_ast/src/ast.rs

@@ -1902,10 +1902,6 @@ pub enum TyKind {
     Never,
     /// A tuple (`(A, B, C, D,...)`).
     Tup(Vec<P<Ty>>),
-    /// An anonymous struct type i.e. `struct { foo: Type }`
-    AnonymousStruct(Vec<FieldDef>, bool),
-    /// An anonymous union type i.e. `union { bar: Type }`
-    AnonymousUnion(Vec<FieldDef>, bool),
     /// A path (`module::module::...::Type`), optionally
     /// "qualified", e.g., `<Vec<T> as SomeTrait>::SomeType`.
     ///

compiler/rustc_ast/src/mut_visit.rs

@@ -484,9 +484,6 @@ 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::AnonymousStruct(fields, ..) | TyKind::AnonymousUnion(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/visit.rs

@@ -407,9 +407,6 @@ pub fn walk_ty<'a, V: Visitor<'a>>(visitor: &mut V, typ: &'a Ty) {
         TyKind::Typeof(ref expression) => visitor.visit_anon_const(expression),
         TyKind::Infer | TyKind::ImplicitSelf | TyKind::Err => {}
         TyKind::MacCall(ref mac) => visitor.visit_mac_call(mac),
-        TyKind::AnonymousStruct(ref fields, ..) | TyKind::AnonymousUnion(ref fields, ..) => {
-            walk_list!(visitor, visit_field_def, fields)
-        }
         TyKind::Never | TyKind::CVarArgs => {}
     }
 }

compiler/rustc_ast_lowering/src/item.rs

@@ -749,10 +749,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    pub(super) fn lower_field_def(
-        &mut self,
-        (index, f): (usize, &FieldDef),
-    ) -> hir::FieldDef<'hir> {
+    fn lower_field_def(&mut self, (index, f): (usize, &FieldDef)) -> hir::FieldDef<'hir> {
         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
             let t = self.lower_path_ty(
                 &f.ty,

compiler/rustc_ast_lowering/src/lib.rs

@@ -1290,15 +1290,6 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         let kind = match t.kind {
             TyKind::Infer => hir::TyKind::Infer,
             TyKind::Err => hir::TyKind::Err,
-            // FIXME(unnamed_fields): IMPLEMENTATION IN PROGRESS
-            TyKind::AnonymousStruct(ref _fields, _recovered) => {
-                self.sess.struct_span_err(t.span, "anonymous structs are unimplemented").emit();
-                hir::TyKind::Err
-            }
-            TyKind::AnonymousUnion(ref _fields, _recovered) => {
-                self.sess.struct_span_err(t.span, "anonymous unions are unimplemented").emit();
-                hir::TyKind::Err
-            }
             TyKind::Slice(ref ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
             TyKind::Ptr(ref mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),
             TyKind::Rptr(ref region, ref mt) => {

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -668,7 +668,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session) {
         // involved, so we only emit errors where there are no other parsing errors.
         gate_all!(destructuring_assignment, "destructuring assignments are unstable");
     }
-    gate_all!(unnamed_fields, "unnamed fields are not yet fully implemented");
 
     // All uses of `gate_all!` below this point were added in #65742,
     // and subsequently disabled (with the non-early gating readded).

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -985,14 +985,6 @@ impl<'a> State<'a> {
                 }
                 self.pclose();
             }
-            ast::TyKind::AnonymousStruct(ref fields, ..) => {
-                self.s.word("struct");
-                self.print_record_struct_body(fields, ty.span);
-            }
-            ast::TyKind::AnonymousUnion(ref fields, ..) => {
-                self.s.word("union");
-                self.print_record_struct_body(fields, ty.span);
-            }
             ast::TyKind::Paren(ref typ) => {
                 self.popen();
                 self.print_type(typ);

compiler/rustc_feature/src/active.rs

@@ -639,9 +639,6 @@ declare_features! (
     /// Allows specifying the as-needed link modifier
     (active, native_link_modifiers_as_needed, "1.53.0", Some(81490), None),
 
-    /// Allows unnamed fields of struct and union type
-    (incomplete, unnamed_fields, "1.53.0", Some(49804), None),
-
     /// Allows qualified paths in struct expressions, struct patterns and tuple struct patterns.
     (active, more_qualified_paths, "1.54.0", Some(86935), None),
 

compiler/rustc_parse/src/parser/item.rs

@@ -1234,7 +1234,7 @@ impl<'a> Parser<'a> {
         Ok((class_name, ItemKind::Union(vdata, generics)))
     }
 
-    pub(super) fn parse_record_struct_body(
+    fn parse_record_struct_body(
         &mut self,
         adt_ty: &str,
     ) -> PResult<'a, (Vec<FieldDef>, /* recovered */ bool)> {
@@ -1468,28 +1468,19 @@ impl<'a> Parser<'a> {
     fn parse_field_ident(&mut self, adt_ty: &str, lo: Span) -> PResult<'a, Ident> {
         let (ident, is_raw) = self.ident_or_err()?;
         if !is_raw && ident.is_reserved() {
-            if ident.name == kw::Underscore {
-                self.sess.gated_spans.gate(sym::unnamed_fields, lo);
+            let err = if self.check_fn_front_matter(false) {
+                let _ = self.parse_fn(&mut Vec::new(), |_| true, lo);
+                let mut err = self.struct_span_err(
+                    lo.to(self.prev_token.span),
+                    &format!("functions are not allowed in {} definitions", adt_ty),
+                );
+                err.help("unlike in C++, Java, and C#, functions are declared in `impl` blocks");
+                err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
+                err
             } else {
-                let err = if self.check_fn_front_matter(false) {
-                    // We use `parse_fn` to get a span for the function
-                    if let Err(mut db) = self.parse_fn(&mut Vec::new(), |_| true, lo) {
-                        db.delay_as_bug();
-                    }
-                    let mut err = self.struct_span_err(
-                        lo.to(self.prev_token.span),
-                        &format!("functions are not allowed in {} definitions", adt_ty),
-                    );
-                    err.help(
-                        "unlike in C++, Java, and C#, functions are declared in `impl` blocks",
-                    );
-                    err.help("see https://doc.rust-lang.org/book/ch05-03-method-syntax.html for more information");
-                    err
-                } else {
-                    self.expected_ident_found()
-                };
-                return Err(err);
-            }
+                self.expected_ident_found()
+            };
+            return Err(err);
         }
         self.bump();
         Ok(ident)

compiler/rustc_parse/src/parser/ty.rs

@@ -226,19 +226,6 @@ impl<'a> Parser<'a> {
             }
         } else if self.eat_keyword(kw::Impl) {
             self.parse_impl_ty(&mut impl_dyn_multi)?
-        } else if self.token.is_keyword(kw::Union)
-            && self.look_ahead(1, |t| t == &token::OpenDelim(token::Brace))
-        {
-            self.bump();
-            let (fields, recovered) = self.parse_record_struct_body("union")?;
-            let span = lo.to(self.prev_token.span);
-            self.sess.gated_spans.gate(sym::unnamed_fields, span);
-            TyKind::AnonymousUnion(fields, recovered)
-        } else if self.eat_keyword(kw::Struct) {
-            let (fields, recovered) = self.parse_record_struct_body("struct")?;
-            let span = lo.to(self.prev_token.span);
-            self.sess.gated_spans.gate(sym::unnamed_fields, span);
-            TyKind::AnonymousStruct(fields, recovered)
         } else if self.is_explicit_dyn_type() {
             self.parse_dyn_ty(&mut impl_dyn_multi)?
         } else if self.eat_lt() {

compiler/rustc_span/src/symbol.rs

@@ -1358,7 +1358,6 @@ symbols! {
         unix,
         unlikely,
         unmarked_api,
-        unnamed_fields,
         unpin,
         unreachable,
         unreachable_code,