[interop][SwiftToCxx] add some helper methods to work with Swift's Optional in C++

Author: hyp

lib/PrintAsClang/ClangSyntaxPrinter.cpp

@@ -354,3 +354,7 @@ void ClangSyntaxPrinter::printIncludeForShimHeader(StringRef headerName) {
   os << "#include <swiftToCxx/" << headerName << ">\n";
   os << "#endif\n";
 }
+
+void ClangSyntaxPrinter::printDefine(StringRef macroName) {
+  os << "#define " << macroName << "\n";
+}

lib/PrintAsClang/ClangSyntaxPrinter.h

@@ -187,6 +187,9 @@ class ClangSyntaxPrinter {
   // Print the #include sequence for the specified C++ interop shim header.
   void printIncludeForShimHeader(StringRef headerName);
 
+  // Print the #define for the given macro.
+  void printDefine(StringRef macroName);
+
 protected:
   raw_ostream &os;
 };

lib/PrintAsClang/PrintClangValueType.cpp

@@ -140,6 +140,10 @@ static void addCppExtensionsToStdlibType(const NominalTypeDecl *typeDecl,
             "passDirect_Swift_String(_getOpaquePointer())));\n";
       os << "  }\n";
     });
+  } else if (typeDecl == typeDecl->getASTContext().getOptionalDecl()) {
+    // Add additional methods for the `Optional` declaration.
+    printer.printDefine("SWIFT_CXX_INTEROP_OPTIONAL_MIXIN");
+    printer.printIncludeForShimHeader("_SwiftStdlibCxxOverlay.h");
   }
 }
 

lib/PrintAsClang/_SwiftCxxInteroperability.h

@@ -25,6 +25,9 @@
 #include <malloc.h>
 #endif
 
+// FIXME: Use always_inline, artificial.
+#define SWIFT_INLINE_THUNK inline
+
 namespace swift {
 namespace _impl {
 

lib/PrintAsClang/_SwiftStdlibCxxOverlay.h

@@ -14,6 +14,26 @@
 #error "no C++"
 #endif
 
+#ifdef SWIFT_CXX_INTEROP_OPTIONAL_MIXIN
+
+/// True when the Optional has a value.
+SWIFT_INLINE_THUNK operator bool() const noexcept { return *this != none; }
+
+/// Returns the value stored in the Optional.
+///
+/// The returned value is copied using the appropriate Swift / C++ copy
+/// semantics.
+SWIFT_INLINE_THUNK T_0_0 get() const
+    noexcept(noexcept(getUnsafelyUnwrapped())) {
+  // FIXME: Fail with source location.
+  return getUnsafelyUnwrapped();
+}
+
+#undef SWIFT_CXX_INTEROP_OPTIONAL_MIXIN
+
+#else
+// out-of-class overlay for Swift standard library.
+
 static_assert(sizeof(_impl::_impl_String) >= 0,
               "included outside of stdlib bindings");
 
@@ -70,3 +90,5 @@ template <class T>
 inline cxxOverlay::IterationEndSentinel end(const Array<T> &) {
   return {};
 }
+
+#endif

test/Interop/SwiftToCxx/stdlib/optional/optional-execution.cpp

@@ -84,9 +84,12 @@ int main() {
   {
     auto val = createCIntOpt(2);
     takeCIntOpt(val);
+    assert((bool)val);
     assert(val.isSome());
     assert(val.getUnsafelyUnwrapped() == 2);
+    assert(val.get() == 2);
     resetOpt(val);
+    assert(!(bool)val);
     assert(val.isNone());
     takeCIntOpt(val);
   }
@@ -95,9 +98,12 @@ int main() {
   {
     auto val = createSmallStructOpt(0xFA);
     takeSmallStructOpt(val);
+    assert((bool)val);
     assert(val.isSome());
     assert(val.getUnsafelyUnwrapped().getX() == 0xFA);
+    assert(val.get().getX() == 0xFA);
     resetOpt(val);
+    assert(!(bool)val);
     assert(val.isNone());
     takeSmallStructOpt(val);
   }