[BitwiseCopyable] Ban indirect enums and cases.

Enums which are entirely indirect or which have indirect cases are never
trivial and hence cannot conform to BitwiseCopyable.

Author: nate-chandler

include/swift/AST/DiagnosticsSema.def

@@ -7609,6 +7609,12 @@ ERROR(escapable_requires_feature_flag,none,
       ())
 ERROR(non_bitwise_copyable_type_class,none,
       "class cannot conform to 'BitwiseCopyable'", ())
+ERROR(non_bitwise_copyable_type_indirect_enum,none,
+      "indirect enum cannot conform to 'BitwiseCopyable'", ())
+ERROR(non_bitwise_copyable_type_indirect_enum_element,none,
+      "enum with indirect case cannot conform to 'BitwiseCopyable'", ())
+NOTE(note_non_bitwise_copyable_type_indirect_enum_element,none,
+     "indirect case is here", ())
 ERROR(non_bitwise_copyable_type_noncopyable,none,
       "noncopyable type cannot conform to 'BitwiseCopyable'", ())
 ERROR(non_bitwise_copyable_type_nonescapable,none,

lib/Sema/TypeCheckBitwise.cpp

@@ -115,6 +115,16 @@ bool BitwiseCopyableStorageVisitor::visitMemberDecl(ValueDecl *decl, Type ty) {
   storage = decl;
   SWIFT_DEFER { storage = nullptr; };
 
+  auto *element = dyn_cast<EnumElementDecl>(decl);
+  if (element && element->isIndirect()) {
+    if (!isImplicit(check)) {
+      nominal->diagnose(diag::non_bitwise_copyable_type_indirect_enum_element);
+      element->diagnose(diag::note_non_bitwise_copyable_type_indirect_enum_element);
+    }
+    invalid = true;
+    return true;
+  }
+
   // Fields with unowned(unsafe) ownership are bitwise-copyable.
   auto *roa = decl->getAttrs().getAttribute<ReferenceOwnershipAttr>();
   if (roa && roa->get() == ReferenceOwnership::Unmanaged) {
@@ -244,6 +254,14 @@ static bool checkBitwiseCopyableInstanceStorage(NominalTypeDecl *nominal,
     return true;
   }
 
+  auto *ed = dyn_cast<EnumDecl>(nominal);
+  if (ed && ed->isIndirect()) {
+    if (!isImplicit(check)) {
+      nominal->diagnose(diag::non_bitwise_copyable_type_indirect_enum);
+    }
+    return true;
+  }
+
   BitwiseCopyableStorageVisitor visitor(nominal, dc, check);
 
   return visitor.visit(nominal, dc) || visitor.invalid;

test/Sema/bitwise_copyable_2.swift

@@ -15,3 +15,13 @@ struct S_Implicit_Noncopyable : ~Copyable {}
 struct S_Explicit_With_Any_BitwiseCopyable : _BitwiseCopyable {
   var a: any _BitwiseCopyable // expected-error {{non_bitwise_copyable_type_member}}
 }
+
+struct S {}
+
+indirect enum E_Explicit_Indirect : _BitwiseCopyable { // expected-error {{non_bitwise_copyable_type_indirect_enum}}
+  case s(S)
+}
+
+enum E_Explicit_Indirect_Case : _BitwiseCopyable { // expected-error {{non_bitwise_copyable_type_indirect_enum_element}}
+  indirect case s(S) // expected-note {{note_non_bitwise_copyable_type_indirect_enum_element}}
+}