[Interop][SwiftToCxx] Introduces swift::Expected

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -780,6 +780,7 @@ EmittedClangHeaderDependencyInfo swift::printModuleContentsAsCxx(
     os << "#ifndef SWIFT_CXX_INTEROP_HIDE_STL_OVERLAY\n";
     os << "#include <string>\n";
     os << "#endif\n";
+    os << "#include <new>\n";
     // Embed an overlay for the standard library.
     ClangSyntaxPrinter(moduleOS).printIncludeForShimHeader(
         "_SwiftStdlibCxxOverlay.h");

lib/PrintAsClang/PrintClangFunction.cpp

@@ -688,6 +688,8 @@ ClangRepresentation DeclAndTypeClangFunctionPrinter::printFunctionSignature(
       ClangRepresentation::representable;
 
   // Print out the return type.
+  if (FD->hasThrows() && outputLang == OutputLanguageMode::Cxx)
+    os << "Swift::ThrowingResult<";
   if (kind == FunctionSignatureKind::CFunctionProto) {
     // First, verify that the C++ return type is representable.
     {
@@ -740,7 +742,8 @@ ClangRepresentation DeclAndTypeClangFunctionPrinter::printFunctionSignature(
             .isUnsupported())
       return resultingRepresentation;
   }
-
+  if (FD->hasThrows() && outputLang == OutputLanguageMode::Cxx)
+    os << ">";
   os << ' ';
   if (const auto *typeDecl = modifiers.qualifierContext)
     ClangSyntaxPrinter(os).printNominalTypeQualifier(
@@ -1241,14 +1244,43 @@ void DeclAndTypeClangFunctionPrinter::printCxxThunkBody(
   // Create the condition and the statement to throw an exception.
   if (hasThrows) {
     os << "  if (opaqueError != nullptr)\n";
+    os << "#ifdef __cpp_exceptions\n";
     os << "    throw (Swift::Error(opaqueError));\n";
-  }
+    os << "#else\n";
+    if (resultTy->isVoid()) {
+      os << "    return SWIFT_RETURN_THUNK(void, Swift::Error(opaqueError));\n";
+      os << "#endif\n";
+    } else {
+      auto directResultType = signature.getDirectResultType();
+      printDirectReturnOrParamCType(
+          *directResultType, resultTy, moduleContext, os, cPrologueOS,
+          typeMapping, interopContext, [&]() {
+            os << "    return SWIFT_RETURN_THUNK(";
+            OptionalTypeKind retKind;
+            Type objTy;
+            std::tie(objTy, retKind) =
+                DeclAndTypePrinter::getObjectTypeAndOptionality(FD, resultTy);
 
-  // Return the function result value if it doesn't throw.
-  if (!resultTy->isVoid() && hasThrows) {
-    os << "\n";
-    os << "return returnValue;\n";
+            auto s = printClangFunctionReturnType(objTy, retKind, const_cast<ModuleDecl *>(moduleContext),
+                                                  OutputLanguageMode::Cxx);
+            os << ", Swift::Error(opaqueError));\n";
+            os << "#endif\n";
+
+            // Return the function result value if it doesn't throw.
+            if (!resultTy->isVoid() && hasThrows) {
+              os << "\n";
+              os << "  return SWIFT_RETURN_THUNK(";
+              printClangFunctionReturnType(
+                  objTy, retKind, const_cast<ModuleDecl *>(moduleContext),
+                  OutputLanguageMode::Cxx);
+              os << ", returnValue);\n";
+            }
+
+            assert(!s.isUnsupported());
+          });
+    }
   }
+
 }
 
 static StringRef getConstructorName(const AbstractFunctionDecl *FD) {

lib/PrintAsClang/_SwiftStdlibCxxOverlay.h

@@ -132,6 +132,8 @@ inline const void *_Nullable getErrorMetadata() {
   return ptr2;
 }
 
+#ifndef SWIFT_CXX_INTEROP_HIDE_SWIFT_ERROR
+
 class Error {
 public:
   Error() {}
@@ -179,4 +181,196 @@ class Error {
   void *_Nonnull opaqueValue = nullptr;
 };
 
+namespace _impl {
+
+constexpr inline std::size_t max(std::size_t a, std::size_t b) {
+  return a > b ? a : b;
+}
+
+} // namespace _impl
+
+/// The Expected class has either an error or an value.
+template<class T>
+class Expected {
+public:
+
+  /// Default
+  constexpr Expected() noexcept {
+    new (&buffer) Error();
+    has_val = false;
+  }
+
+  constexpr Expected(const Swift::Error& error_val) noexcept {
+    new (&buffer) Error(error_val);
+    has_val = false;
+  }
+
+  constexpr Expected(const T &val) noexcept {
+    new (&buffer) T(val);
+    has_val = true;
+  }
+
+  /// Copy
+  constexpr Expected(Expected const& other) noexcept {
+    if (other.has_value())
+      new (&buffer) T(other.value());
+    else
+      new (&buffer) Error(other.error());
+
+    has_val = other.has_value();
+  }
+
+  /// Move
+  // FIXME: Implement move semantics when move Swift values is possible
+  constexpr Expected(Expected&&) noexcept { abort(); }
+
+  ~Expected() noexcept {
+    if (has_value())
+      reinterpret_cast<const T *>(buffer)->~T();
+    else
+      reinterpret_cast<Swift::Error *>(buffer)->~Error();
+  }
+
+  /// assignment
+  constexpr auto operator=(Expected&& other) noexcept = delete;
+  constexpr auto operator=(Expected&) noexcept = delete;
+
+  /// For accessing T's members
+  constexpr T const *_Nonnull operator->() const noexcept {
+    if (!has_value())
+      abort();
+    return reinterpret_cast<const T *>(buffer);
+  }
+
+  constexpr T *_Nonnull operator->() noexcept {
+    if (!has_value())
+      abort();
+    return reinterpret_cast<T *>(buffer);
+  }
+
+  /// Getting reference to T
+  constexpr T const &operator*() const & noexcept {
+    if (!has_value())
+      abort();
+    return reinterpret_cast<const T &>(buffer);
+  }
+
+  constexpr T &operator*() & noexcept {
+    if (!has_value())
+      abort();
+    return reinterpret_cast<T &>(buffer);
+  }
+
+  constexpr explicit operator bool() const noexcept { return has_value(); }
+
+  // Get value, if not exists abort
+  constexpr T const& value() const& {
+    if (!has_value())
+      abort();
+    return *reinterpret_cast<const T *>(buffer);
+  }
+
+  constexpr T& value() & {
+    if (!has_value())
+      abort();
+    return *reinterpret_cast<T *>(buffer);
+  }
+
+  // Get error
+  constexpr Swift::Error const& error() const& {
+    if (has_value())
+      abort();
+    return reinterpret_cast<const Swift::Error&>(buffer);
+  }
+
+  constexpr Swift::Error& error() & {
+    if (has_value())
+      abort();
+    return reinterpret_cast<Swift::Error&>(buffer);
+  }
+
+  constexpr bool has_value() const noexcept { return has_val; }
+
+private:
+  alignas(_impl::max(alignof(T), alignof(Swift::Error))) char buffer[_impl::max(sizeof(T), sizeof(Swift::Error))];
+  bool has_val;
+};
+
+template<>
+class Expected<void> {
+public:
+  /// Default
+  Expected() noexcept {
+    new (&buffer) Error();
+    has_val = false;
+  }
+
+  Expected(const Swift::Error& error_val) noexcept {
+    new (&buffer) Error(error_val);
+    has_val = false;
+  }
+
+
+  /// Copy
+  Expected(Expected const& other) noexcept {
+    if (other.has_value())
+      abort();
+    else
+      new (&buffer) Error(other.error());
+
+    has_val = other.has_value();
+  }
+
+  /// Move
+  // FIXME: Implement move semantics when move swift values is possible
+  [[noreturn]] Expected(Expected&&) noexcept { abort(); }
+
+  ~Expected() noexcept {
+    reinterpret_cast<Swift::Error *>(buffer)->~Error();
+  }
+
+  /// assignment
+  constexpr auto operator=(Expected&& other) noexcept = delete;
+  constexpr auto operator=(Expected&) noexcept = delete;
+
+
+  constexpr explicit operator bool() const noexcept { return has_value(); }
+
+  // Get error
+  constexpr Swift::Error const& error() const& {
+    if (has_value())
+      abort();
+    return reinterpret_cast<const Swift::Error&>(buffer);
+  }
+
+  constexpr Swift::Error& error() & {
+    if (has_value())
+      abort();
+    return reinterpret_cast<Swift::Error&>(buffer);
+  }
+
+  constexpr bool has_value() const noexcept { return has_val; }
+private:
+  alignas(alignof(Swift::Error)) char buffer[sizeof(Swift::Error)];
+  bool has_val;
+};
+
+#ifdef __cpp_exceptions
+
+template<class T>
+using ThrowingResult = T;
+
+#define SWIFT_RETURN_THUNK(T, v) v
+
+#else
+
+template<class T>
+using ThrowingResult = Swift::Expected<T>;
+
+#define SWIFT_RETURN_THUNK(T, v) Swift::Expected<T>(v)
+
+#endif
+
+#endif // SWIFT_CXX_INTEROP_HIDE_SWIFT_ERROR
+
 #endif