Lowering unnamed fields and anonymous adt

compiler/rustc_ast/src/ast.rs

@@ -2107,9 +2107,9 @@ pub enum TyKind {
     /// A tuple (`(A, B, C, D,...)`).
     Tup(ThinVec<P<Ty>>),
     /// An anonymous struct type i.e. `struct { foo: Type }`
-    AnonStruct(ThinVec<FieldDef>),
+    AnonStruct(NodeId, ThinVec<FieldDef>),
     /// An anonymous union type i.e. `union { bar: Type }`
-    AnonUnion(ThinVec<FieldDef>),
+    AnonUnion(NodeId, ThinVec<FieldDef>),
     /// A path (`module::module::...::Type`), optionally
     /// "qualified", e.g., `<Vec<T> as SomeTrait>::SomeType`.
     ///
@@ -2161,6 +2161,10 @@ impl TyKind {
             None
         }
     }
+
+    pub fn is_anon_adt(&self) -> bool {
+        matches!(self, TyKind::AnonStruct(..) | TyKind::AnonUnion(..))
+    }
 }
 
 /// Syntax used to declare a trait object.

compiler/rustc_ast/src/mut_visit.rs

@@ -514,7 +514,8 @@ 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) => {
+        TyKind::AnonStruct(id, fields) | TyKind::AnonUnion(id, fields) => {
+            vis.visit_id(id);
             fields.flat_map_in_place(|field| vis.flat_map_field_def(field));
         }
     }

compiler/rustc_ast/src/visit.rs

@@ -450,7 +450,7 @@ 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, ..) => {
+        TyKind::AnonStruct(_, ref fields) | TyKind::AnonUnion(_, ref fields) => {
             walk_list!(visitor, visit_field_def, fields)
         }
     }

compiler/rustc_ast_lowering/src/item.rs

@@ -720,7 +720,10 @@ impl<'hir> LoweringContext<'_, 'hir> {
         }
     }
 
-    fn lower_field_def(&mut self, (index, f): (usize, &FieldDef)) -> hir::FieldDef<'hir> {
+    pub(super) fn lower_field_def(
+        &mut self,
+        (index, f): (usize, &FieldDef),
+    ) -> hir::FieldDef<'hir> {
         let ty = if let TyKind::Path(qself, path) = &f.ty.kind {
             let t = self.lower_path_ty(
                 &f.ty,

compiler/rustc_ast_lowering/src/lib.rs

@@ -1288,17 +1288,44 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TyKind::Err => {
                 hir::TyKind::Err(self.dcx().span_delayed_bug(t.span, "TyKind::Err lowered"))
             }
-            // FIXME(unnamed_fields): IMPLEMENTATION IN PROGRESS
-            #[allow(rustc::untranslatable_diagnostic)]
-            #[allow(rustc::diagnostic_outside_of_impl)]
-            TyKind::AnonStruct(ref _fields) => {
-                hir::TyKind::Err(self.dcx().span_err(t.span, "anonymous structs are unimplemented"))
-            }
-            // FIXME(unnamed_fields): IMPLEMENTATION IN PROGRESS
-            #[allow(rustc::untranslatable_diagnostic)]
-            #[allow(rustc::diagnostic_outside_of_impl)]
-            TyKind::AnonUnion(ref _fields) => {
-                hir::TyKind::Err(self.dcx().span_err(t.span, "anonymous unions are unimplemented"))
+            // Lower the anonymous structs or unions in a nested lowering context.
+            //
+            // ```
+            // struct Foo {
+            //     _: union {
+            // //     ^__________________  <-- within the nested lowering context,
+            //         /* fields */ //   |     we lower all fields defined into an
+            //     } //                  |     owner node of struct or union item
+            // //  ^_____________________|
+            // }
+            // ```
+            TyKind::AnonStruct(node_id, fields) | TyKind::AnonUnion(node_id, fields) => {
+                // Here its `def_id` is created in `build_reduced_graph`.
+                let def_id = self.local_def_id(*node_id);
+                debug!(?def_id);
+                let owner_id = hir::OwnerId { def_id };
+                self.with_hir_id_owner(*node_id, |this| {
+                    let fields = this.arena.alloc_from_iter(
+                        fields.iter().enumerate().map(|f| this.lower_field_def(f)),
+                    );
+                    let span = t.span;
+                    let variant_data = hir::VariantData::Struct { fields, recovered: false };
+                    // FIXME: capture the generics from the outer adt.
+                    let generics = hir::Generics::empty();
+                    let kind = match t.kind {
+                        TyKind::AnonStruct(..) => hir::ItemKind::Struct(variant_data, generics),
+                        TyKind::AnonUnion(..) => hir::ItemKind::Union(variant_data, generics),
+                        _ => unreachable!(),
+                    };
+                    hir::OwnerNode::Item(this.arena.alloc(hir::Item {
+                        ident: Ident::new(kw::Empty, span),
+                        owner_id,
+                        kind,
+                        span: this.lower_span(span),
+                        vis_span: this.lower_span(span.shrink_to_lo()),
+                    }))
+                });
+                hir::TyKind::AnonAdt(hir::ItemId { owner_id })
             }
             TyKind::Slice(ty) => hir::TyKind::Slice(self.lower_ty(ty, itctx)),
             TyKind::Ptr(mt) => hir::TyKind::Ptr(self.lower_mt(mt, itctx)),

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -219,8 +219,8 @@ impl<'a> AstValidator<'a> {
                     }
                 }
             }
-            TyKind::AnonStruct(ref fields, ..) | TyKind::AnonUnion(ref fields, ..) => {
-                walk_list!(self, visit_field_def, fields)
+            TyKind::AnonStruct(_, ref fields) | TyKind::AnonUnion(_, ref fields) => {
+                walk_list!(self, visit_struct_field_def, fields)
             }
             _ => visit::walk_ty(self, t),
         }

compiler/rustc_ast_pretty/src/pprust/state.rs

@@ -1003,11 +1003,11 @@ impl<'a> State<'a> {
                 }
                 self.pclose();
             }
-            ast::TyKind::AnonStruct(fields) => {
+            ast::TyKind::AnonStruct(_, fields) => {
                 self.head("struct");
                 self.print_record_struct_body(fields, ty.span);
             }
-            ast::TyKind::AnonUnion(fields) => {
+            ast::TyKind::AnonUnion(_, fields) => {
                 self.head("union");
                 self.print_record_struct_body(fields, ty.span);
             }

compiler/rustc_builtin_macros/src/deriving/clone.rs

@@ -110,7 +110,9 @@ fn cs_clone_simple(
                 && !seen_type_names.insert(name)
             {
                 // Already produced an assertion for this type.
-            } else {
+                // Anonymous structs or unions must be eliminated as they cannot be
+                // type parameters.
+            } else if !field.ty.kind.is_anon_adt() {
                 // let _: AssertParamIsClone<FieldTy>;
                 super::assert_ty_bounds(
                     cx,

compiler/rustc_builtin_macros/src/deriving/mod.rs

@@ -123,6 +123,8 @@ fn assert_ty_bounds(
     span: Span,
     assert_path: &[Symbol],
 ) {
+    // Deny anonymous structs or unions to avoid wierd errors.
+    assert!(!ty.kind.is_anon_adt(), "Anonymous structs or unions cannot be type parameters");
     // Generate statement `let _: assert_path<ty>;`.
     let span = cx.with_def_site_ctxt(span);
     let assert_path = cx.path_all(span, true, cx.std_path(assert_path), vec![GenericArg::Type(ty)]);

compiler/rustc_hir/src/def.rs

@@ -8,6 +8,7 @@ use rustc_data_structures::unord::UnordMap;
 use rustc_macros::HashStable_Generic;
 use rustc_span::def_id::{DefId, LocalDefId};
 use rustc_span::hygiene::MacroKind;
+use rustc_span::symbol::kw;
 use rustc_span::Symbol;
 
 use std::array::IntoIter;
@@ -225,6 +226,7 @@ impl DefKind {
 
     pub fn def_path_data(self, name: Symbol) -> DefPathData {
         match self {
+            DefKind::Struct | DefKind::Union if name == kw::Empty => DefPathData::AnonAdt,
             DefKind::Mod
             | DefKind::Struct
             | DefKind::Union

compiler/rustc_hir/src/definitions.rs

@@ -287,6 +287,8 @@ pub enum DefPathData {
     /// An existential `impl Trait` type node.
     /// Argument position `impl Trait` have a `TypeNs` with their pretty-printed name.
     OpaqueTy,
+    /// An anonymous struct or union type i.e. `struct { foo: Type }` or `union { bar: Type }`
+    AnonAdt,
 }
 
 impl Definitions {
@@ -409,8 +411,9 @@ impl DefPathData {
         match *self {
             TypeNs(name) if name == kw::Empty => None,
             TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
+
             Impl | ForeignMod | CrateRoot | Use | GlobalAsm | Closure | Ctor | AnonConst
-            | OpaqueTy => None,
+            | OpaqueTy | AnonAdt => None,
         }
     }
 
@@ -431,6 +434,7 @@ impl DefPathData {
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst => DefPathDataName::Anon { namespace: sym::constant },
             OpaqueTy => DefPathDataName::Anon { namespace: sym::opaque },
+            AnonAdt => DefPathDataName::Anon { namespace: sym::anon_adt },
         }
     }
 }

compiler/rustc_hir/src/hir.rs

@@ -2587,6 +2587,8 @@ pub enum TyKind<'hir> {
     Never,
     /// A tuple (`(A, B, C, D, ...)`).
     Tup(&'hir [Ty<'hir>]),
+    /// An anonymous struct or union type i.e. `struct { foo: Type }` or `union { foo: Type }`
+    AnonAdt(ItemId),
     /// A path to a type definition (`module::module::...::Type`), or an
     /// associated type (e.g., `<Vec<T> as Trait>::Type` or `<T>::Target`).
     ///

compiler/rustc_hir/src/intravisit.rs

@@ -852,6 +852,9 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) {
         }
         TyKind::Typeof(ref expression) => visitor.visit_anon_const(expression),
         TyKind::Infer | TyKind::InferDelegation(..) | TyKind::Err(_) => {}
+        TyKind::AnonAdt(item_id) => {
+            visitor.visit_nested_item(item_id);
+        }
     }
 }
 

compiler/rustc_hir_analysis/messages.ftl

@@ -123,6 +123,28 @@ hir_analysis_field_already_declared =
     .label = field already declared
     .previous_decl_label = `{$field_name}` first declared here
 
+hir_analysis_field_already_declared_both_nested =
+    field `{$field_name}` is already declared
+    .label = field `{$field_name}` declared in this unnamed field
+    .nested_field_decl_note = field `{$field_name}` declared here
+    .previous_decl_label = `{$field_name}` first declared here in this unnamed field
+    .previous_nested_field_decl_note = field `{$field_name}` first declared here
+
+hir_analysis_field_already_declared_current_nested =
+    field `{$field_name}` is already declared
+    .label = field `{$field_name}` declared in this unnamed field
+    .nested_field_decl_note = field `{$field_name}` declared here
+    .previous_decl_label = `{$field_name}` first declared here
+
+hir_analysis_field_already_declared_nested_help =
+    fields from the type of this unnamed field are considered fields of the outer type
+
+hir_analysis_field_already_declared_previous_nested =
+    field `{$field_name}` is already declared
+    .label = field already declared
+    .previous_decl_label = `{$field_name}` first declared here in this unnamed field
+    .previous_nested_field_decl_note = field `{$field_name}` first declared here
+
 hir_analysis_function_not_found_in_trait = function not found in this trait
 
 hir_analysis_function_not_have_default_implementation = function doesn't have a default implementation
@@ -420,6 +442,19 @@ hir_analysis_typeof_reserved_keyword_used =
 hir_analysis_unconstrained_opaque_type = unconstrained opaque type
     .note = `{$name}` must be used in combination with a concrete type within the same {$what}
 
+hir_analysis_unnamed_fields_repr_field_defined = unnamed field defined here
+
+hir_analysis_unnamed_fields_repr_field_missing_repr_c =
+    named type of unnamed field must have `#[repr(C)]` representation
+    .label = unnamed field defined here
+    .field_ty_label = `{$field_ty}` defined here
+    .suggestion = add `#[repr(C)]` to this {$field_adt_kind}
+
+hir_analysis_unnamed_fields_repr_missing_repr_c =
+    {$adt_kind} with unnamed fields must have `#[repr(C)]` representation
+    .label = {$adt_kind} `{$adt_name}` defined here
+    .suggestion = add `#[repr(C)]` to this {$adt_kind}
+
 hir_analysis_unrecognized_atomic_operation =
     unrecognized atomic operation function: `{$op}`
     .label = unrecognized atomic operation

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2457,6 +2457,19 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             hir::TyKind::Tup(fields) => {
                 Ty::new_tup_from_iter(tcx, fields.iter().map(|t| self.ast_ty_to_ty(t)))
             }
+            hir::TyKind::AnonAdt(item_id) => {
+                let did = item_id.owner_id.def_id;
+                let adt_def = tcx.adt_def(did);
+                let generics = tcx.generics_of(did);
+
+                debug!("ast_ty_to_ty_inner(AnonAdt): generics={:?}", generics);
+                let args = ty::GenericArgs::for_item(tcx, did.to_def_id(), |param, _| {
+                    tcx.mk_param_from_def(param)
+                });
+                debug!("ast_ty_to_ty_inner(AnonAdt): args={:?}", args);
+
+                Ty::new_adt(tcx, adt_def, tcx.mk_args(args))
+            }
             hir::TyKind::BareFn(bf) => {
                 require_c_abi_if_c_variadic(tcx, bf.decl, bf.abi, ast_ty.span);
 

compiler/rustc_hir_analysis/src/check/check.rs

@@ -80,6 +80,7 @@ fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId) {
 
     check_transparent(tcx, def);
     check_packed(tcx, span, def);
+    check_unnamed_fields(tcx, def);
 }
 
 fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId) {
@@ -89,6 +90,58 @@ fn check_union(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     check_transparent(tcx, def);
     check_union_fields(tcx, span, def_id);
     check_packed(tcx, span, def);
+    check_unnamed_fields(tcx, def);
+}
+
+/// Check the representation of adts with unnamed fields.
+fn check_unnamed_fields(tcx: TyCtxt<'_>, def: ty::AdtDef<'_>) {
+    if def.is_enum() {
+        return;
+    }
+    let variant = def.non_enum_variant();
+    if !variant.has_unnamed_fields() {
+        return;
+    }
+    if !def.is_anonymous() {
+        let adt_kind = def.descr();
+        let span = tcx.def_span(def.did());
+        let unnamed_fields = variant
+            .fields
+            .iter()
+            .filter(|f| f.is_unnamed())
+            .map(|f| {
+                let span = tcx.def_span(f.did);
+                errors::UnnamedFieldsReprFieldDefined { span }
+            })
+            .collect::<Vec<_>>();
+        debug_assert_ne!(unnamed_fields.len(), 0, "expect unnamed fields in this adt");
+        let adt_name = tcx.item_name(def.did());
+        if !def.repr().c() {
+            tcx.dcx().emit_err(errors::UnnamedFieldsRepr::MissingReprC {
+                span,
+                adt_kind,
+                adt_name,
+                unnamed_fields,
+                sugg_span: span.shrink_to_lo(),
+            });
+        }
+    }
+    for field in variant.fields.iter().filter(|f| f.is_unnamed()) {
+        let field_ty = tcx.type_of(field.did).instantiate_identity();
+        if let Some(adt) = field_ty.ty_adt_def()
+            && !adt.is_anonymous()
+            && !adt.repr().c()
+        {
+            let field_ty_span = tcx.def_span(adt.did());
+            tcx.dcx().emit_err(errors::UnnamedFieldsRepr::FieldMissingReprC {
+                span: tcx.def_span(field.did),
+                field_ty_span,
+                field_ty,
+                field_adt_kind: adt.descr(),
+                sugg_span: field_ty_span.shrink_to_lo(),
+            });
+        }
+    }
 }
 
 /// Check that the fields of the `union` do not need dropping.