[cxx-interop] mark C++ classes with trivial_abi attribute as unavailable in Swift

(cherry picked from commit 2c4188b)

Author: hyp

lib/ClangImporter/ImportDecl.cpp

@@ -2712,6 +2712,17 @@ namespace {
       if (!result)
         return nullptr;
 
+      if (decl->hasAttr<clang::TrivialABIAttr>()) {
+        // We cannot yet represent trivial_abi C++ records in Swift.
+        // Clang tells us such type can be passed in registers, so
+        // we avoid using AddressOnly type-layout for such type, which means
+        // that it then does not use C++'s copy and destroy semantics from
+        // Swift.
+        Impl.markUnavailable(cast<ValueDecl>(result),
+                             "C++ classes with `trivial_abi` Clang attribute "
+                             "are not yet available in Swift");
+      }
+
       if (auto classDecl = dyn_cast<ClassDecl>(result)) {
         validateForeignReferenceType(decl, classDecl);
 

test/Interop/Cxx/class/clang-trivial-abi.swift

@@ -0,0 +1,33 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// RUN: %target-swift-ide-test -print-module -module-to-print=Test -I %t/Inputs -source-filename=x -enable-experimental-cxx-interop | %FileCheck %s
+// RUN: %target-swift-frontend -typecheck -I %t/Inputs  %t/test.swift  -enable-experimental-cxx-interop -verify
+
+//--- Inputs/module.modulemap
+module Test {
+    header "test.h"
+    requires cplusplus
+}
+
+//--- Inputs/test.h
+
+class TrivialABIRecord {
+    int x = 0;
+public:
+    TrivialABIRecord() {}
+    ~TrivialABIRecord() {
+    }
+}
+__attribute__((trivial_abi));
+
+// CHECK: @available(*, unavailable, message: "C++ classes with `trivial_abi` Clang attribute are not yet available in Swift")
+// CHECK-NEXT: struct TrivialABIRecord {
+
+//--- test.swift
+
+import Test
+
+func test() {
+    let _ = TrivialABIRecord() // expected-error{{'TrivialABIRecord' is unavailable: C++ classes with `trivial_abi` Clang attribute are not yet available in Swift}}
+}