[cxx-interop] Prevent Swift from importing fields marked with [[no_unique_address]]

Author: susmonteiro

include/swift/AST/DiagnosticsClangImporter.def

@@ -373,5 +373,8 @@ NOTE(ptr_to_nonescapable,none,
      "pointer to non-escapable type %0 cannot be imported",
      (const clang::Type*))
 
+WARNING(unsupported_attribute, none,
+        "Swift doesn't support fields marked with %0", (StringRef))
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

lib/ClangImporter/ImportDecl.cpp

@@ -4383,6 +4383,15 @@ namespace {
       std::optional<ImportedName> correctSwiftName;
       ImportedName importedName;
 
+      if (decl->hasAttr<clang::NoUniqueAddressAttr>()) {
+        // FIXME: Swift doesn't support fields marked with [[no_unique_address]] rdar://148437848
+
+        SourceLoc loc = Impl.importSourceLoc(decl->getLocation());
+        Impl.diagnose(loc, diag::unsupported_attribute, "[[no_unique_addr]]");
+
+        return nullptr;
+      }
+
       std::tie(importedName, correctSwiftName) = importFullName(decl);
       if (!importedName) {
         return nullptr;

test/Interop/Cxx/stdlib/use-std-string.swift

@@ -490,4 +490,11 @@ StdStringTestSuite.test("pass as a default argument") {
 }
 #endif
 
+StdStringTestSuite.test("print std::string") {
+    let cxxString: std.string = "Hello"
+    print(cxxString)
+    let swiftString = String(cxxString)
+    print(swiftString)
+}
+
 runAllTests()