[interop][SwiftToCxx] expose subscript getter for Array's operator []

Author: hyp

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -873,7 +873,8 @@ class DeclAndTypePrinter::Implementation
 
   void printAbstractFunctionAsMethod(AbstractFunctionDecl *AFD,
                                      bool isClassMethod,
-                                     bool isNSUIntegerSubscript = false) {
+                                     bool isNSUIntegerSubscript = false,
+                                     const SubscriptDecl *SD = nullptr) {
     printDocumentationComment(AFD);
 
     Optional<ForeignAsyncConvention> asyncConvention =
@@ -910,10 +911,15 @@ class DeclAndTypePrinter::Implementation
           os, owningPrinter.prologueOS, owningPrinter.typeMapping,
           owningPrinter.interopContext, owningPrinter);
       if (auto *accessor = dyn_cast<AccessorDecl>(AFD)) {
-        declPrinter.printCxxPropertyAccessorMethod(
-            typeDeclContext, accessor, funcABI->getSignature(),
-            funcABI->getSymbolName(), resultTy,
-            /*isDefinition=*/false);
+        if (SD)
+          declPrinter.printCxxSubscriptAccessorMethod(
+              typeDeclContext, accessor, funcABI->getSignature(),
+              funcABI->getSymbolName(), resultTy, /*isDefinition=*/false);
+        else
+          declPrinter.printCxxPropertyAccessorMethod(
+              typeDeclContext, accessor, funcABI->getSignature(),
+              funcABI->getSymbolName(), resultTy,
+              /*isDefinition=*/false);
       } else {
         declPrinter.printCxxMethod(typeDeclContext, AFD,
                                    funcABI->getSignature(),
@@ -927,11 +933,15 @@ class DeclAndTypePrinter::Implementation
           owningPrinter);
 
       if (auto *accessor = dyn_cast<AccessorDecl>(AFD)) {
-
-        defPrinter.printCxxPropertyAccessorMethod(
-            typeDeclContext, accessor, funcABI->getSignature(),
-            funcABI->getSymbolName(), resultTy,
-            /*isDefinition=*/true);
+        if (SD)
+          defPrinter.printCxxSubscriptAccessorMethod(
+              typeDeclContext, accessor, funcABI->getSignature(),
+              funcABI->getSymbolName(), resultTy, /*isDefinition=*/true);
+        else
+          defPrinter.printCxxPropertyAccessorMethod(
+              typeDeclContext, accessor, funcABI->getSignature(),
+              funcABI->getSymbolName(), resultTy,
+              /*isDefinition=*/true);
       } else {
         defPrinter.printCxxMethod(typeDeclContext, AFD, funcABI->getSignature(),
                                   funcABI->getSymbolName(), resultTy,
@@ -1818,8 +1828,14 @@ class DeclAndTypePrinter::Implementation
   }
 
   void visitSubscriptDecl(SubscriptDecl *SD) {
-    if (outputLang == OutputLanguageMode::Cxx)
+    if (outputLang == OutputLanguageMode::Cxx) {
+      if (!SD->isInstanceMember())
+        return;
+      auto *getter = SD->getOpaqueAccessor(AccessorKind::Get);
+      printAbstractFunctionAsMethod(getter, false,
+                                    /*isNSUIntegerSubscript=*/false, SD);
       return;
+    }
     assert(SD->isInstanceMember() && "static subscripts not supported");
 
     bool isNSUIntegerSubscript = false;

lib/PrintAsClang/PrintClangFunction.cpp

@@ -1208,6 +1208,32 @@ void DeclAndTypeClangFunctionPrinter::printCxxPropertyAccessorMethod(
   os << "  }\n";
 }
 
+void DeclAndTypeClangFunctionPrinter::printCxxSubscriptAccessorMethod(
+    const NominalTypeDecl *typeDeclContext, const AccessorDecl *accessor,
+    const LoweredFunctionSignature &signature, StringRef swiftSymbolName,
+    Type resultTy, bool isDefinition) {
+  assert(accessor->isGetter());
+  FunctionSignatureModifiers modifiers;
+  if (isDefinition)
+    modifiers.qualifierContext = typeDeclContext;
+  modifiers.isInline = true;
+  modifiers.isConst = true;
+  auto result =
+      printFunctionSignature(accessor, signature, "operator []", resultTy,
+                             FunctionSignatureKind::CxxInlineThunk, modifiers);
+  assert(!result.isUnsupported() && "C signature should be unsupported too!");
+  if (!isDefinition) {
+    os << ";\n";
+    return;
+  }
+  os << " {\n";
+  // FIXME: should it be objTy for resultTy?
+  printCxxThunkBody(accessor, signature, swiftSymbolName,
+                    accessor->getModuleContext(), resultTy,
+                    accessor->getParameters());
+  os << "  }\n";
+}
+
 bool DeclAndTypeClangFunctionPrinter::hasKnownOptionalNullableCxxMapping(
     Type type) {
   if (auto optionalObjectType = type->getOptionalObjectType()) {

lib/PrintAsClang/PrintClangFunction.h

@@ -123,6 +123,12 @@ class DeclAndTypeClangFunctionPrinter {
                                       StringRef swiftSymbolName, Type resultTy,
                                       bool isDefinition);
 
+  /// Print the C++ subscript method.
+  void printCxxSubscriptAccessorMethod(
+      const NominalTypeDecl *typeDeclContext, const AccessorDecl *accessor,
+      const LoweredFunctionSignature &signature, StringRef swiftSymbolName,
+      Type resultTy, bool isDefinition);
+
   /// Print Swift type as C/C++ type, as the return type of a C/C++ function.
   ClangRepresentation
   printClangFunctionReturnType(Type ty, OptionalTypeKind optKind,

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

@@ -48,6 +48,8 @@ int main() {
     UseArray::printArray(val);
     assert(val.getCount() == 1);
     assert(val.getCapacity() >= 1);
+    auto zeroInt = val[0];
+    assert(zeroInt == -11);
     auto firstInt = val.remove(0);
     assert(firstInt == -11);
     assert(val.getCount() == 0);

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

@@ -20,6 +20,7 @@
 // CHECK: static inline Array<T_0_0> init();
 // CHECK: inline void append(const T_0_0& newElement);
 // CHECK: inline T_0_0 remove(swift::Int index);
+// CHECK: inline T_0_0 operator [](swift::Int index) const;
 // CHECK: inline swift::Int getCount() const;
 // CHECK: inline swift::Int getCapacity() const;