[interop][SwiftToCxx] start emitting bindings for Swift class types

This includes release on destruction, and correctly returning class values from Swift to C++.

lib/PrintAsClang/CMakeLists.txt

@@ -5,6 +5,7 @@ add_swift_host_library(swiftPrintAsClang STATIC
   ModuleContentsWriter.cpp
   PrimitiveTypeMapping.cpp
   PrintAsClang.cpp
+  PrintClangClassType.cpp
   PrintClangFunction.cpp
   PrintClangValueType.cpp
   PrintSwiftToClangCoreScaffold.cpp

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -13,6 +13,7 @@
 #include "DeclAndTypePrinter.h"
 #include "ClangSyntaxPrinter.h"
 #include "PrimitiveTypeMapping.h"
+#include "PrintClangClassType.h"
 #include "PrintClangFunction.h"
 #include "PrintClangValueType.h"
 #include "SwiftToClangInteropContext.h"
@@ -296,6 +297,15 @@ private:
   void visitClassDecl(ClassDecl *CD) {
     printDocumentationComment(CD);
 
+    if (outputLang == OutputLanguageMode::Cxx) {
+      // FIXME: Non objc class.
+      // FIXME: Print availability.
+      ClangClassTypePrinter(os).printClassTypeDecl(CD, []() {
+        // FIXME: print class body.
+      });
+      return;
+    }
+
     // This is just for testing, so we check explicitly for the attribute instead
     // of asking if the class is weak imported. If the class has availability,
     // we'll print a SWIFT_AVAILABLE() which implies __attribute__((weak_imported))

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -605,6 +605,8 @@ public:
 
       if (auto ED = dyn_cast<EnumDecl>(D)) {
         success = writeEnum(ED);
+      } else if (auto CD = dyn_cast<ClassDecl>(D)) {
+        success = writeClass(CD);
       } else if (outputLangMode == OutputLanguageMode::Cxx) {
         if (auto FD = dyn_cast<FuncDecl>(D))
           success = writeFunc(FD);
@@ -612,9 +614,7 @@ public:
           success = writeStruct(SD);
         // FIXME: Warn on unsupported exported decl.
       } else if (isa<ValueDecl>(D)) {
-        if (auto CD = dyn_cast<ClassDecl>(D))
-          success = writeClass(CD);
-        else if (auto PD = dyn_cast<ProtocolDecl>(D))
+        if (auto PD = dyn_cast<ProtocolDecl>(D))
           success = writeProtocol(PD);
         else if (auto ED = dyn_cast<FuncDecl>(D))
           success = writeFunc(ED);

lib/PrintAsClang/PrintClangClassType.cpp

@@ -0,0 +1,91 @@
+//===--- PrintClangClassType.cpp - Print class types in C/C++ ---*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "PrintClangClassType.h"
+#include "ClangSyntaxPrinter.h"
+#include "PrintClangValueType.h"
+#include "swift/AST/Decl.h"
+
+using namespace swift;
+
+void ClangClassTypePrinter::printClassTypeDecl(
+    const ClassDecl *typeDecl, llvm::function_ref<void(void)> bodyPrinter) {
+  auto printCxxImplClassName = ClangValueTypePrinter::printCxxImplClassName;
+
+  ClangSyntaxPrinter printer(os);
+
+  // Print out a forward declaration of the "hidden" _impl class.
+  printer.printNamespace(cxx_synthesis::getCxxImplNamespaceName(),
+                         [&](raw_ostream &os) {
+                           os << "class ";
+                           printCxxImplClassName(os, typeDecl);
+                           os << ";\n";
+                         });
+
+  os << "class ";
+  printer.printBaseName(typeDecl);
+  // FIXME: Add support for inherintance.
+  os << " final";
+  os << " {\n";
+  os << "public:\n";
+
+  // Destructor releases the object.
+  os << "  inline ~";
+  printer.printBaseName(typeDecl);
+  os << "() { swift::" << cxx_synthesis::getCxxImplNamespaceName()
+     << "::swift_release(_opaquePointer); }\n";
+
+  // FIXME: move semantics should be restricted?
+  os << "  inline ";
+  printer.printBaseName(typeDecl);
+  os << "(";
+  printer.printBaseName(typeDecl);
+  os << "&&) noexcept = default;\n";
+
+  os << "private:\n";
+  os << "  inline ";
+  printer.printBaseName(typeDecl);
+  os << "(void * _Nonnull ptr) noexcept : _opaquePointer(ptr) {}\n";
+  os << "\n  void * _Nonnull _opaquePointer;\n";
+  os << "  friend class " << cxx_synthesis::getCxxImplNamespaceName() << "::";
+  printCxxImplClassName(os, typeDecl);
+  os << ";\n";
+  os << "};\n\n";
+
+  // Print out the "hidden" _impl class.
+  printer.printNamespace(
+      cxx_synthesis::getCxxImplNamespaceName(), [&](raw_ostream &os) {
+        os << "class ";
+        printCxxImplClassName(os, typeDecl);
+        os << " {\n";
+        os << "public:\n";
+        os << "static inline ";
+        printer.printBaseName(typeDecl);
+        os << " fromUnretained(void * _Nonnull ptr) noexcept { return ";
+        printer.printBaseName(typeDecl);
+        os << "(ptr); }\n";
+        os << "};\n";
+      });
+}
+
+void ClangClassTypePrinter::printClassTypeReturnScaffold(
+    raw_ostream &os, const ClassDecl *type, const ModuleDecl *moduleContext,
+    llvm::function_ref<void(void)> bodyPrinter) {
+  os << "  return ";
+  ClangSyntaxPrinter(os).printModuleNamespaceQualifiersIfNeeded(
+      type->getModuleContext(), moduleContext);
+  os << cxx_synthesis::getCxxImplNamespaceName() << "::";
+  ClangValueTypePrinter::printCxxImplClassName(os, type);
+  os << "::fromUnretained(";
+  bodyPrinter();
+  os << ");\n";
+}

lib/PrintAsClang/PrintClangClassType.h

@@ -0,0 +1,46 @@
+//===--- PrintClangClassType.h - Print class types in C/C++ -----*- C++ -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2022 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_PRINTASCLANG_PRINTCLANGCLASSTYPE_H
+#define SWIFT_PRINTASCLANG_PRINTCLANGCLASSTYPE_H
+
+#include "swift/Basic/LLVM.h"
+#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/raw_ostream.h"
+
+namespace swift {
+
+class ClassDecl;
+class ModuleDecl;
+
+/// Responsible for printing a Swift class decl or in C or C++ mode, to
+/// be included in a Swift module's generated clang header.
+class ClangClassTypePrinter {
+public:
+  ClangClassTypePrinter(raw_ostream &os) : os(os) {}
+
+  /// Print the C++ class definition that corresponds to the given Swift class.
+  void printClassTypeDecl(const ClassDecl *typeDecl,
+                          llvm::function_ref<void(void)> bodyPrinter);
+
+  static void
+  printClassTypeReturnScaffold(raw_ostream &os, const ClassDecl *type,
+                               const ModuleDecl *moduleContext,
+                               llvm::function_ref<void(void)> bodyPrinter);
+
+private:
+  raw_ostream &os;
+};
+
+} // end namespace swift
+
+#endif

lib/PrintAsClang/PrintClangFunction.cpp

@@ -15,6 +15,7 @@
 #include "DeclAndTypePrinter.h"
 #include "OutputLanguageMode.h"
 #include "PrimitiveTypeMapping.h"
+#include "PrintClangClassType.h"
 #include "PrintClangValueType.h"
 #include "SwiftToClangInteropContext.h"
 #include "swift/AST/Decl.h"
@@ -147,6 +148,21 @@ public:
     visitPart(aliasTy->getSinglyDesugaredType(), optionalKind, isInOutParam);
   }
 
+  void visitClassType(ClassType *CT, Optional<OptionalTypeKind> optionalKind,
+                      bool isInOutParam) {
+    // FIXME: handle optionalKind.
+    // FIXME: handle isInOutParam.
+    if (languageMode != OutputLanguageMode::Cxx) {
+      os << "void * _Nonnull";
+      return;
+    }
+    if (typeUseKind == FunctionSignatureTypeUse::ParamType)
+      os << "const ";
+    ClangSyntaxPrinter(os).printBaseName(CT->getDecl());
+    if (typeUseKind == FunctionSignatureTypeUse::ParamType)
+      os << "&";
+  }
+
   void visitEnumType(EnumType *ET, Optional<OptionalTypeKind> optionalKind,
                      bool isInOutParam) {
     visitValueType(ET, optionalKind, isInOutParam);
@@ -559,6 +575,12 @@ void DeclAndTypeClangFunctionPrinter::printCxxThunkBody(
       os << ";\n  return returnValue;\n";
       return;
     }
+    if (auto *classDecl = resultTy->getClassOrBoundGenericClass()) {
+      ClangClassTypePrinter::printClassTypeReturnScaffold(
+          os, classDecl, moduleContext,
+          [&]() { printCallToCFunc(/*additionalParam=*/None); });
+      return;
+    }
     if (auto *decl = resultTy->getNominalOrBoundGenericNominal()) {
       if ((isa<StructDecl>(decl) || isa<EnumDecl>(decl))) {
         bool isIndirect =

stdlib/public/SwiftShims/_SwiftCxxInteroperability.h

@@ -28,6 +28,10 @@
 namespace swift {
 namespace _impl {
 
+extern "C" void *_Nonnull swift_retain(void *_Nonnull) noexcept;
+
+extern "C" void swift_release(void *_Nonnull) noexcept;
+
 inline void *_Nonnull opaqueAlloc(size_t size, size_t align) noexcept {
 #if defined(_WIN32)
   void *r = _aligned_malloc(size, align);

test/Interop/SwiftToCxx/class/swift-class-execution.cpp

@@ -0,0 +1,24 @@
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend %S/swift-class-in-cxx.swift -typecheck -module-name Class -clang-header-expose-public-decls -emit-clang-header-path %t/class.h
+
+// RUN: %target-interop-build-clangxx -c %s -I %t -o %t/swift-class-execution.o
+// RUN: %target-interop-build-swift %S/swift-class-in-cxx.swift -o %t/swift-class-execution -Xlinker %t/swift-class-execution.o -module-name Class -Xfrontend -entry-point-function-name -Xfrontend swiftMain
+
+// RUN: %target-codesign %t/swift-class-execution
+// RUN: %target-run %t/swift-class-execution | %FileCheck %s
+
+// REQUIRES: executable_test
+
+#include <assert.h>
+#include "class.h"
+
+int main() {
+  using namespace Class;
+
+  // Ensure that the class is released.
+  auto x = returnClassWithIntField();
+// CHECK:      init ClassWithIntField
+// CHECK-NEXT: destroy ClassWithIntField
+  return 0;
+}

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

@@ -0,0 +1,61 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -typecheck -module-name Class -clang-header-expose-public-decls -emit-clang-header-path %t/class.h
+// RUN: %FileCheck %s < %t/class.h
+
+// RUN: %check-interop-cxx-header-in-clang(%t/class.h)
+
+public final class ClassWithIntField {
+  let field: Int64
+
+  init() {
+    field = 0
+    print("init ClassWithIntField")
+  }
+  deinit {
+    print("destroy ClassWithIntField")
+  }
+}
+
+// CHECK: namespace Class {
+
+// CHECK: SWIFT_EXTERN void * _Nonnull $s5Class06returnA12WithIntFieldAA0acdE0CyF(void) SWIFT_NOEXCEPT SWIFT_CALL; // returnClassWithIntField()
+
+// CHECK: namespace Class {
+
+// CHECK: namespace _impl {
+// CHECK-EMPTY:
+// CHECK-NEXT: class _impl_ClassWithIntField;
+// CHECK-EMPTY:
+// CHECK-NEXT: } // namespace _impl
+// CHECK-EMPTY:
+// CHECK-NEXT: class ClassWithIntField final {
+// CHECK-NEXT: public:
+// CHECK-NEXT:   inline ~ClassWithIntField() { swift::_impl::swift_release(_opaquePointer); }
+// CHECK-NEXT:   inline ClassWithIntField(ClassWithIntField&&) noexcept = default;
+// CHECK-NEXT: private:
+// CHECK-NEXT:   inline ClassWithIntField(void * _Nonnull ptr) noexcept : _opaquePointer(ptr) {}
+// CHECK-EMPTY:
+// CHECK-NEXT:   void * _Nonnull _opaquePointer;
+// CHECK-NEXT:   friend class _impl::_impl_ClassWithIntField;
+// CHECK-NEXT: };
+// CHECK-EMPTY:
+// CHECK-NEXT:namespace _impl {
+// CHECK-EMPTY:
+// CHECK-NEXT:class _impl_ClassWithIntField {
+// CHECK-NEXT:public:
+// CHECK-NEXT:static inline ClassWithIntField fromUnretained(void * _Nonnull ptr) noexcept { return ClassWithIntField(ptr); }
+// CHECK-NEXT:};
+// CHECK-EMPTY:
+// CHECK-NEXT:} // namespace _impl
+
+public final class register { }
+
+// CHECK: class register_ final {
+
+public func returnClassWithIntField() -> ClassWithIntField {
+  return ClassWithIntField()
+}
+
+// CHECK: inline ClassWithIntField returnClassWithIntField() noexcept SWIFT_WARN_UNUSED_RESULT {
+// CHECK-NEXT:   return _impl::_impl_ClassWithIntField::fromUnretained(_impl::$s5Class06returnA12WithIntFieldAA0acdE0CyF());
+// CHECK-NEXT: }