[interop][SwiftToCxx] add experimental Swift::String -> NSString conversion operator

Author: hyp

lib/PrintAsClang/ClangSyntaxPrinter.cpp

@@ -98,10 +98,23 @@ void ClangSyntaxPrinter::printExternC(
   os << "#endif\n";
 }
 
+void ClangSyntaxPrinter::printObjCBlock(
+    llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const {
+  os << "#if defined(__OBJC__)\n";
+  bodyPrinter(os);
+  os << "\n#endif\n";
+}
+
 void ClangSyntaxPrinter::printSwiftImplQualifier() const {
   os << "swift::" << cxx_synthesis::getCxxImplNamespaceName() << "::";
 }
 
+void ClangSyntaxPrinter::printInlineForThunk() const {
+  // FIXME: make a macro and add 'nodebug', and
+  // migrate all other 'inline' uses.
+  os << "inline __attribute__((always_inline)) ";
+}
+
 void ClangSyntaxPrinter::printNullability(
     Optional<OptionalTypeKind> kind, NullabilityPrintKind printKind) const {
   if (!kind)

lib/PrintAsClang/ClangSyntaxPrinter.h

@@ -70,6 +70,10 @@ class ClangSyntaxPrinter {
   void
   printExternC(llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const;
 
+  /// Print an #ifdef __OBJC__ block.
+  void
+  printObjCBlock(llvm::function_ref<void(raw_ostream &OS)> bodyPrinter) const;
+
   /// Print the `swift::_impl::` namespace qualifier.
   void printSwiftImplQualifier() const;
 
@@ -80,6 +84,8 @@ class ClangSyntaxPrinter {
     ContextSensitive,
   };
 
+  void printInlineForThunk() const;
+
   void printNullability(
       Optional<OptionalTypeKind> kind,
       NullabilityPrintKind printKind = NullabilityPrintKind::After) const;

lib/PrintAsClang/PrintClangValueType.cpp

@@ -87,6 +87,30 @@ void ClangValueTypePrinter::forwardDeclType(raw_ostream &os,
   os << ";\n";
 }
 
+static void addCppExtensionsToStdlibType(const NominalTypeDecl *typeDecl,
+                                         ClangSyntaxPrinter &printer,
+                                         raw_ostream &cPrologueOS) {
+  if (typeDecl == typeDecl->getASTContext().getStringDecl()) {
+    // Perform String -> NSString conversion using
+    // _bridgeToObjectiveCImpl.
+    // FIXME: This is an extension, we should
+    // just expose the method to C once extensions are
+    // supported.
+    cPrologueOS << "SWIFT_EXTERN void *_Nonnull "
+                   "$sSS23_bridgeToObjectiveCImplyXlyF(swift_interop_stub_"
+                   "Swift_String) SWIFT_NOEXCEPT SWIFT_CALL;\n";
+    printer.printObjCBlock([](raw_ostream &os) {
+      os << "  ";
+      ClangSyntaxPrinter(os).printInlineForThunk();
+      os << "operator NSString * _Nonnull () const noexcept {\n";
+      os << "    return (__bridge_transfer NSString "
+            "*)(_impl::$sSS23_bridgeToObjectiveCImplyXlyF(_impl::swift_interop_"
+            "passDirect_Swift_String(_getOpaquePointer())));\n";
+      os << "  }\n";
+    });
+  }
+}
+
 void ClangValueTypePrinter::printValueTypeDecl(
     const NominalTypeDecl *typeDecl,
     llvm::function_ref<void(void)> bodyPrinter) {
@@ -193,6 +217,8 @@ void ClangValueTypePrinter::printValueTypeDecl(
   os << " &&) = default;\n";
 
   bodyPrinter();
+  if (typeDecl->isStdlibDecl())
+    addCppExtensionsToStdlibType(typeDecl, printer, cPrologueOS);
 
   os << "private:\n";
 

test/Interop/SwiftToCxx/lit.local.cfg

@@ -1 +1 @@
-config.suffixes = ['.swift', '.cpp']
+config.suffixes = ['.swift', '.cpp', '.mm']

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

@@ -0,0 +1,68 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -parse-as-library %platform-module-dir/Swift.swiftmodule/%module-target-triple.swiftinterface -enable-library-evolution -disable-objc-attr-requires-foundation-module -typecheck -module-name Swift -parse-stdlib -enable-experimental-cxx-interop -emit-clang-header-path %t/Swift.h  -experimental-skip-all-function-bodies
+
+// RUN: %target-swift-frontend -typecheck %t/create_string.swift -typecheck -module-name StringCreator -enable-experimental-cxx-interop -emit-clang-header-path %t/StringCreator.h
+
+// RUN: %target-interop-build-clangxx -fobjc-arc -c %t/string-to-nsstring.mm -I %t -o %t/swift-stdlib-execution.o
+// RUN: %target-build-swift %t/use_foundation.swift %t/create_string.swift -o %t/swift-stdlib-execution -Xlinker %t/swift-stdlib-execution.o -module-name StringCreator -Xfrontend -entry-point-function-name -Xfrontend swiftMain -lc++
+// RUN: %target-codesign %t/swift-stdlib-execution
+// RUN: %target-run %t/swift-stdlib-execution
+
+// RUN: %target-interop-build-clangxx -fobjc-arc -c %t/string-to-nsstring-one-arc-op.mm -I %t -Xclang -emit-llvm -S -o - -O1 |  %FileCheck --check-prefix=CHECKARC %s
+
+// REQUIRES: executable_test
+// REQUIRES: objc_interop
+
+//--- use_foundation.swift
+import Foundation
+
+//--- create_string.swift
+@_expose(Cxx)
+public func createString(_ ptr: UnsafePointer<CChar>) -> String {
+    return String(cString: ptr)
+}
+
+//--- string-to-nsstring-one-arc-op.mm
+
+#include "Swift.h"
+
+int main() {
+  using namespace Swift;
+  auto emptyString = String::init();
+  NSString *nsStr = emptyString;
+}
+
+// CHECKARC: %[[VAL:.*]] = call swiftcc i8* @"$sSS23_bridgeToObjectiveCImplyXlyF"
+// CHECKARC: call i8* @llvm.objc.autorelease(i8* %[[VAL]])
+// CHECKARC: @llvm.objc.
+// CHECKARC-SAME: autorelease(i8*)
+// CHECKARC-NOT: @llvm.objc.
+
+//--- string-to-nsstring.mm
+
+#include <cassert>
+#include <string>
+#include "Swift.h"
+#include "StringCreator.h"
+
+int main() {
+  using namespace Swift;
+
+  auto emptyString = String::init();
+
+  {
+    NSString *nsStr = emptyString;
+    assert(std::string(nsStr.UTF8String) == "");
+    assert([nsStr isEqualToString:@""]);
+  }
+
+  auto aStr = StringCreator::createString("hello");
+  {
+    NSString *nsStr = aStr;
+    assert(std::string(nsStr.UTF8String) == "hello");
+    assert([nsStr isEqualToString:@"hello"]);
+  }
+  return 0;
+}

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

@@ -14,6 +14,12 @@
 // CHECK:  }
 // CHECK-NEXT:  inline String(String &&) = default;
 // CHECK-NEXT:  static inline String init();
+// CHECK-NEXT:  #if defined(__OBJC__)
+// CHECK-NEXT:  inline __attribute__((always_inline)) operator NSString * _Nonnull () const noexcept {
+// CHECK-NEXT:    return (__bridge_transfer NSString *)(_impl::$sSS23_bridgeToObjectiveCImplyXlyF(_impl::swift_interop_passDirect_Swift_String(_getOpaquePointer())));
+// CHECK-NEXT:   }
+// CHECK-EMPTY:
+// CHECK-NEXT:  #endif
 // CHECK-NEXT: private:
 
 // CHECK: } // namespace Swift