[interop][SwiftToCxx] support NSString -> Swift String bridging in C++

Author: hyp

lib/PrintAsClang/PrintClangValueType.cpp

@@ -131,6 +131,10 @@ static void addCppExtensionsToStdlibType(const NominalTypeDecl *typeDecl,
     cPrologueOS << "SWIFT_EXTERN void *_Nonnull "
                    "$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF(swift_interop_stub_"
                    "Swift_String) SWIFT_NOEXCEPT SWIFT_CALL;\n";
+    cPrologueOS << "SWIFT_EXTERN swift_interop_stub_Swift_String "
+                   "$sSS10FoundationE36_"
+                   "unconditionallyBridgeFromObjectiveCySSSo8NSStringCSgFZ("
+                   "void * _Nullable) SWIFT_NOEXCEPT SWIFT_CALL;\n";
     printer.printObjCBlock([](raw_ostream &os) {
       os << "  ";
       ClangSyntaxPrinter(os).printInlineForThunk();
@@ -139,6 +143,17 @@ static void addCppExtensionsToStdlibType(const NominalTypeDecl *typeDecl,
             "*)(_impl::$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF(_impl::swift_interop_"
             "passDirect_Swift_String(_getOpaquePointer())));\n";
       os << "  }\n";
+      os << "static ";
+      ClangSyntaxPrinter(os).printInlineForThunk();
+      os << "String init(NSString * _Nonnull nsString) noexcept {\n";
+      os << "    auto result = _make();\n";
+      os << "    auto res = "
+            "_impl::$sSS10FoundationE36_"
+            "unconditionallyBridgeFromObjectiveCySSSo8NSStringCSgFZ((__bridge "
+            "void *)nsString);\n";
+      os << "    memcpy(result._getOpaquePointer(), &res, sizeof(res));\n";
+      os << "    return result;\n";
+      os << "  }\n";
     });
   } else if (typeDecl == typeDecl->getASTContext().getOptionalDecl()) {
     // Add additional methods for the `Optional` declaration.

test/Interop/SwiftToCxx/stdlib/string/string-to-nsstring.mm

@@ -61,5 +61,13 @@ int main() {
     assert(std::string(nsStr.UTF8String) == "hello");
     assert([nsStr isEqualToString:@"hello"]);
   }
+
+  {
+    NSString *nsStr = @"nsstr";
+    auto str = String::init(nsStr);
+    NSString *nsStr2 = str;
+    assert(std::string(nsStr.UTF8String) == "nsstr");
+    assert([nsStr2 isEqualToString:nsStr]);
+  }
   return 0;
 }

test/Interop/SwiftToCxx/stdlib/swift-stdlib-in-cxx.swift

@@ -79,6 +79,12 @@
 // CHECK-NEXT:  inline __attribute__((always_inline)) operator NSString * _Nonnull () const noexcept {
 // CHECK-NEXT:    return (__bridge_transfer NSString *)(_impl::$sSS10FoundationE19_bridgeToObjectiveCSo8NSStringCyF(_impl::swift_interop_passDirect_Swift_String(_getOpaquePointer())));
 // CHECK-NEXT:   }
+// CHECK-NEXT:  static inline __attribute__((always_inline)) String init(NSString * _Nonnull nsString) noexcept {
+// CHECK-NEXT:  auto result = _make();
+// CHECK-NEXT:  auto res = _impl::$sSS10FoundationE36_unconditionallyBridgeFromObjectiveCySSSo8NSStringCSgFZ((__bridge void *)nsString);
+// CHECK-NEXT:  memcpy(result._getOpaquePointer(), &res, sizeof(res));
+// CHECK-NEXT:  return result;
+// CHECK-NEXT:  }
 // CHECK-EMPTY:
 // CHECK-NEXT:  #endif
 // CHECK-NEXT: private: