[cxx-interop] disallow use of non-trivial C++ types in @objc declarations

Even though such types can technically be represented in C++, Swift's @objc support does not support them

rdar://114163485

Author: hyp

include/swift/AST/DiagnosticsSema.def

@@ -6084,6 +6084,8 @@ NOTE(not_objc_error_protocol_composition,none,
      "in Objective-C", ())
 NOTE(not_objc_empty_tuple,none,
       "empty tuple type cannot be represented in Objective-C", ())
+NOTE(not_objc_non_trivial_cxx_class,none,
+     "non-trivial C++ classes cannot be represented in Objective-C", ())
 NOTE(not_objc_tuple,none,
       "tuples cannot be represented in Objective-C", ())
 NOTE(not_objc_swift_class,none,

lib/AST/Type.cpp

@@ -3096,6 +3096,17 @@ getForeignRepresentable(Type type, ForeignLanguage language,
 
     case ForeignLanguage::ObjectiveC:
       if (isa<StructDecl>(nominal) || isa<EnumDecl>(nominal)) {
+        // Non-trivial C++ classes and structures are not
+        // supported by @objc attribute, even though they can
+        // be represented in Objective-C++.
+        if (auto *cxxRec = dyn_cast_or_null<clang::CXXRecordDecl>(
+                nominal->getClangDecl())) {
+          if (cxxRec->hasNonTrivialCopyConstructor() ||
+              cxxRec->hasNonTrivialMoveConstructor() ||
+              cxxRec->hasNonTrivialDestructor())
+            return failure();
+        }
+
         // Optional structs are not representable in (Objective-)C if they
         // originally came from C, whether or not they are bridged, unless they
         // came from swift_newtype. If they are defined in Swift, they are only

lib/Sema/TypeCheckDeclObjC.cpp

@@ -179,6 +179,13 @@ static void diagnoseTypeNotRepresentableInObjC(const DeclContext *DC,
 
   // Special diagnostic for structs.
   if (auto *SD = T->getStructOrBoundGenericStruct()) {
+    if (isa_and_nonnull<clang::CXXRecordDecl>(SD->getClangDecl())) {
+      // This can be a non-trivial C++ record.
+      diags.diagnose(TypeRange.Start, diag::not_objc_non_trivial_cxx_class)
+          .highlight(TypeRange)
+          .limitBehavior(behavior);
+      return;
+    }
     diags.diagnose(TypeRange.Start, diag::not_objc_swift_struct)
         .highlight(TypeRange)
         .limitBehavior(behavior);

test/Interop/Cxx/objc-correctness/at-objc-api-using-non-trivial-cxx.swift

@@ -0,0 +1,60 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -typecheck -I %t/Inputs -cxx-interoperability-mode=default -verify %t/test.swift
+
+// REQUIRES: objc_interop
+
+//--- Inputs/header.h
+
+class Trivial {
+public:
+  int x;
+};
+
+class NonTrivial {
+public:
+  NonTrivial(const NonTrivial &other) : x(other.x) {}
+  ~NonTrivial() { }
+
+private:
+  int x;
+};
+
+struct NonTrivialDestrOnly {
+  ~NonTrivialDestrOnly() { }
+
+private:
+  int x;
+};
+
+//--- Inputs/module.modulemap
+
+module NonTrivial {
+    header "header.h"
+    export *
+}
+
+//--- test.swift
+
+import Foundation
+import NonTrivial
+
+@objc
+class ObjCObject: NSObject {
+  @objc var prop: NonTrivial // expected-error {{property cannot be marked @objc because its type cannot be represented in Objective-C}}
+  // expected-note@-1 {{non-trivial C++ classes cannot be represented in Objective-C}}
+
+  @objc var trivProp: Trivial
+
+  override init() { fatalError() }
+
+  @objc func getNonTrivial() -> NonTrivialDestrOnly { // expected-error {{method cannot be marked @objc because its result type cannot be represented in Objective-C}}
+    // expected-note@-1 {{non-trivial C++ classes cannot be represented in Objective-C}}
+    fatalError()
+  }
+
+  @objc func getTrivial() -> Trivial {
+    return Trivial(x: 11)
+  }
+}