Check representation of unnamed fields

compiler/rustc_hir_analysis/messages.ftl

@@ -422,6 +422,12 @@ 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_missing_repr_c =
+    {$adt_kind} with unnamed fields must have `#[repr(C)]` representation
+    .label = {$adt_kind} defined here
+
+hir_analysis_unnamed_fields_repr_defined = unnamed field defined here
+
 hir_analysis_unrecognized_atomic_operation =
     unrecognized atomic operation function: `{$op}`
     .label = unrecognized atomic operation

compiler/rustc_hir_analysis/src/check/check.rs

@@ -79,6 +79,7 @@ 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) {
@@ -88,6 +89,40 @@ 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<'_>) {
+    let adt_kind = match def.adt_kind() {
+        ty::AdtKind::Struct => "struct",
+        ty::AdtKind::Union => "union",
+        _ => return,
+    };
+    let variant = def.non_enum_variant();
+    if variant.has_unnamed_fields() {
+        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::UnnamedFieldsReprDefined { span }
+            })
+            .collect::<Vec<_>>();
+        debug_assert_ne!(unnamed_fields.len(), 0, "expect unnamed fields in this adt");
+        if !def.is_anonymous() {
+            let repr =  def.repr();
+            if !repr.c() {
+                tcx.dcx().emit_err(errors::UnnamedFieldsReprMissingReprC {
+                    span,
+                    adt_kind,
+                    unnamed_fields,
+                });
+            }
+        }
+    }
 }
 
 /// Check that the fields of the `union` do not need dropping.

compiler/rustc_hir_analysis/src/collect.rs

@@ -989,7 +989,11 @@ fn adt_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::AdtDef<'_> {
     };
 
     let is_anonymous = item.ident.name == kw::Empty;
-    let repr = tcx.repr_options_of_def(def_id.to_def_id());
+    let repr = if is_anonymous {
+        tcx.adt_def(tcx.local_parent(def_id)).repr()
+    } else {
+        tcx.repr_options_of_def(def_id.to_def_id())
+    };
     let (kind, variants) = match &item.kind {
         ItemKind::Enum(def, _) => {
             let mut distance_from_explicit = 0;

compiler/rustc_hir_analysis/src/errors.rs

@@ -1447,3 +1447,21 @@ pub struct OnlyCurrentTraitsPointerSugg<'a> {
     pub mut_key: &'a str,
     pub ptr_ty: Ty<'a>,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_unnamed_fields_repr_missing_repr_c)]
+pub struct UnnamedFieldsReprMissingReprC {
+    #[primary_span]
+    #[label]
+    pub span: Span,
+    pub adt_kind: &'static str,
+    #[subdiagnostic]
+    pub unnamed_fields: Vec<UnnamedFieldsReprDefined>,
+}
+
+#[derive(Subdiagnostic)]
+#[label(hir_analysis_unnamed_fields_repr_defined)]
+pub struct UnnamedFieldsReprDefined {
+    #[primary_span]
+    pub span: Span,
+}

compiler/rustc_resolve/src/def_collector.rs

@@ -80,6 +80,22 @@ impl<'a, 'b, 'tcx> DefCollector<'a, 'b, 'tcx> {
             let name = field.ident.map_or_else(|| sym::integer(index(self)), |ident| ident.name);
             let def = self.create_def(field.id, name, DefKind::Field, field.span);
             self.with_parent(def, |this| visit::walk_field_def(this, field));
+            self.visit_anon_adt(&field.ty);
+        }
+    }
+
+    fn visit_anon_adt(&mut self, ty: &'a Ty) {
+        let def_kind = match &ty.kind {
+            TyKind::AnonStruct(..) => DefKind::Struct,
+            TyKind::AnonUnion(..) => DefKind::Union,
+            _ => return,
+        };
+        match &ty.kind {
+            TyKind::AnonStruct(node_id, _) | TyKind::AnonUnion(node_id, _) => {
+                let def_id = self.create_def(*node_id, kw::Empty, def_kind, ty.span);
+                self.with_parent(def_id, |this| visit::walk_ty(this, ty));
+            }
+            _ => {},
         }
     }
 
@@ -320,19 +336,8 @@ impl<'a, 'b, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'b, 'tcx> {
     fn visit_ty(&mut self, ty: &'a Ty) {
         match &ty.kind {
             TyKind::MacCall(..) => self.visit_macro_invoc(ty.id),
-            TyKind::AnonStruct(node_id, fields) | TyKind::AnonUnion(node_id, fields) => {
-                let def_kind = match &ty.kind {
-                    TyKind::AnonStruct(..) => DefKind::Struct,
-                    TyKind::AnonUnion(..) => DefKind::Union,
-                    _ => unreachable!(),
-                };
-                let def_id = self.create_def(*node_id, kw::Empty, def_kind, ty.span);
-                self.with_parent(def_id, |this| {
-                    for f in fields {
-                        this.visit_field_def(f);
-                    }
-                });
-            }
+            // Anonymous structs or unions are visited later after defined.
+            TyKind::AnonStruct(..) | TyKind::AnonUnion(..) => {}
             _ => visit::walk_ty(self, ty),
         }
     }

tests/mir-opt/unnamed-fields/field_access.bar.SimplifyCfg-initial.after.mir

@@ -26,7 +26,7 @@ fn bar(_1: Bar) -> () {
         StorageDead(_2);
         StorageLive(_4);
         StorageLive(_5);
-        _5 = ((_1.1: Bar::_::{anon_adt#0}).0: i8);
+        _5 = ((_1.1: Bar::{anon_adt#0}).0: i8);
         _4 = access::<i8>(move _5) -> [return: bb2, unwind: bb5];
     }
 
@@ -35,7 +35,7 @@ fn bar(_1: Bar) -> () {
         StorageDead(_4);
         StorageLive(_6);
         StorageLive(_7);
-        _7 = ((_1.1: Bar::_::{anon_adt#0}).1: bool);
+        _7 = ((_1.1: Bar::{anon_adt#0}).1: bool);
         _6 = access::<bool>(move _7) -> [return: bb3, unwind: bb5];
     }
 
@@ -44,7 +44,7 @@ fn bar(_1: Bar) -> () {
         StorageDead(_6);
         StorageLive(_8);
         StorageLive(_9);
-        _9 = (((_1.2: Bar::_::{anon_adt#0}).0: Bar::_::{anon_adt#0}::_::{anon_adt#0}).0: [u8; 1]);
+        _9 = (((_1.2: Bar::{anon_adt#1}).0: Bar::{anon_adt#1}::{anon_adt#0}).0: [u8; 1]);
         _8 = access::<[u8; 1]>(move _9) -> [return: bb4, unwind: bb5];
     }
 

tests/mir-opt/unnamed-fields/field_access.foo.SimplifyCfg-initial.after.mir

@@ -24,7 +24,7 @@ fn foo(_1: Foo) -> () {
         StorageDead(_2);
         StorageLive(_4);
         StorageLive(_5);
-        _5 = ((_1.1: Foo::_::{anon_adt#0}).0: i8);
+        _5 = ((_1.1: Foo::{anon_adt#0}).0: i8);
         _4 = access::<i8>(move _5) -> [return: bb2, unwind: bb5];
     }
 
@@ -33,7 +33,7 @@ fn foo(_1: Foo) -> () {
         StorageDead(_4);
         StorageLive(_6);
         StorageLive(_7);
-        _7 = ((_1.1: Foo::_::{anon_adt#0}).1: bool);
+        _7 = ((_1.1: Foo::{anon_adt#0}).1: bool);
         _6 = access::<bool>(move _7) -> [return: bb3, unwind: bb5];
     }
 
@@ -42,7 +42,7 @@ fn foo(_1: Foo) -> () {
         StorageDead(_6);
         StorageLive(_8);
         StorageLive(_9);
-        _9 = (((_1.2: Foo::_::{anon_adt#0}).0: Foo::_::{anon_adt#0}::_::{anon_adt#0}).0: [u8; 1]);
+        _9 = (((_1.2: Foo::{anon_adt#1}).0: Foo::{anon_adt#1}::{anon_adt#0}).0: [u8; 1]);
         _8 = access::<[u8; 1]>(move _9) -> [return: bb4, unwind: bb5];
     }
 

tests/ui/union/unnamed-fields/repr_check.rs

@@ -0,0 +1,27 @@
+#![allow(incomplete_features)]
+#![feature(unnamed_fields)]
+
+struct A { //~ ERROR struct with unnamed fields must have `#[repr(C)]` representation
+    _: struct {
+        a: i32,
+    }
+}
+
+union B { //~ ERROR union with unnamed fields must have `#[repr(C)]` representation
+    _: struct {
+        b: i32,
+    }
+}
+
+#[derive(Clone, Copy)]
+struct Foo {}
+
+struct C { //~ ERROR struct with unnamed fields must have `#[repr(C)]` representation
+    _: Foo,
+}
+
+union D { //~ ERROR union with unnamed fields must have `#[repr(C)]` representation
+    _: Foo,
+}
+
+fn main() {}

tests/ui/union/unnamed-fields/repr_check.stderr

@@ -0,0 +1,38 @@
+error: struct with unnamed fields must have `#[repr(C)]` representation
+  --> $DIR/repr_check.rs:4:1
+   |
+LL |   struct A {
+   |   ^^^^^^^^ struct defined here
+LL | /     _: struct {
+LL | |         a: i32,
+LL | |     }
+   | |_____- unnamed field defined here
+
+error: union with unnamed fields must have `#[repr(C)]` representation
+  --> $DIR/repr_check.rs:10:1
+   |
+LL |   union B {
+   |   ^^^^^^^ union defined here
+LL | /     _: struct {
+LL | |         b: i32,
+LL | |     }
+   | |_____- unnamed field defined here
+
+error: struct with unnamed fields must have `#[repr(C)]` representation
+  --> $DIR/repr_check.rs:19:1
+   |
+LL | struct C {
+   | ^^^^^^^^ struct defined here
+LL |     _: Foo,
+   |     ------ unnamed field defined here
+
+error: union with unnamed fields must have `#[repr(C)]` representation
+  --> $DIR/repr_check.rs:23:1
+   |
+LL | union D {
+   | ^^^^^^^ union defined here
+LL |     _: Foo,
+   |     ------ unnamed field defined here
+
+error: aborting due to 4 previous errors
+