Implement projectExistentialAndUnwrapClass

Implement a version of projectExistential tailored for LLDB. There are 2
differences when projecting existentials for LLDB:

1 - When it comes to existentials, LLDB stores the address of the error
    pointer, which must be dereferenced.
2 - When the existential wraps a class type, LLDB expects the address
    returned is the class instance itself and not the address of the
    reference.

This patch also adapts the swift reflection test machinery to test
projectExistentialAndUnwrapClass as well. This is done by exposing
the new functionality from swift reflection test.  It is tested in
existentials.swift, and ensures that the typeref information is
exactly the same as what is expected from projectExistential,
except the out address.

Author: augusto2112

include/swift/Reflection/ReflectionContext.h

@@ -92,7 +92,7 @@ class ReflectionContext
   using super = remote::MetadataReader<Runtime, TypeRefBuilder>;
   using super::readMetadata;
   using super::readObjCClassName;
-
+  using super::readResolvedPointerValue;
   std::unordered_map<typename super::StoredPointer, const TypeInfo *> Cache;
 
   /// All buffers we need to keep around long term. This will automatically free them
@@ -789,6 +789,52 @@ class ReflectionContext
     }
   }
 
+  llvm::Optional<std::pair<const TypeRef *, RemoteAddress>>
+  getDynamicTypeAndAddressClassExistential(RemoteAddress ExistentialAddress) {
+    auto PointerValue =
+        readResolvedPointerValue(ExistentialAddress.getAddressData());
+    if (!PointerValue)
+      return {};
+    auto Result = readMetadataFromInstance(*PointerValue);
+    if (!Result)
+      return {};
+    auto TypeResult = readTypeFromMetadata(Result.getValue());
+    if (!TypeResult)
+      return {};
+    return {{std::move(TypeResult), RemoteAddress(*PointerValue)}};
+  }
+
+  llvm::Optional<std::pair<const TypeRef *, RemoteAddress>>
+  getDynamicTypeAndAddressErrorExistential(RemoteAddress ExistentialAddress,
+                                           bool *IsBridgedError = nullptr) {
+    auto Result = readMetadataAndValueErrorExistential(ExistentialAddress);
+    if (!Result)
+      return {};
+
+    auto TypeResult =
+        readTypeFromMetadata(Result->MetadataAddress.getAddressData());
+    if (!TypeResult)
+      return {};
+
+    if (IsBridgedError)
+      *IsBridgedError = Result->IsBridgedError;
+
+    return {{TypeResult, Result->PayloadAddress}};
+  }
+
+  llvm::Optional<std::pair<const TypeRef *, RemoteAddress>>
+  getDynamicTypeAndAddressOpaqueExistential(RemoteAddress ExistentialAddress) {
+    auto Result = readMetadataAndValueOpaqueExistential(ExistentialAddress);
+    if (!Result)
+      return {};
+
+    auto TypeResult =
+        readTypeFromMetadata(Result->MetadataAddress.getAddressData());
+    if (!TypeResult)
+      return {};
+    return {{std::move(TypeResult), Result->PayloadAddress}};
+  }
+
   bool projectExistential(RemoteAddress ExistentialAddress,
                           const TypeRef *ExistentialTR,
                           const TypeRef **OutInstanceTR,
@@ -850,6 +896,75 @@ class ReflectionContext
       return false;
     }
   }
+  /// A version of `projectExistential` tailored for LLDB.
+  /// This version dereferences the resulting TypeRef if it wraps
+  /// a class type, it also dereferences the input `ExistentialAddress` before
+  /// attempting to find its dynamic type and address when dealing with error
+  /// existentials.
+  llvm::Optional<std::pair<const TypeRef *, RemoteAddress>>
+  projectExistentialAndUnwrapClass(RemoteAddress ExistentialAddress,
+                                   const TypeRef &ExistentialTR) {
+    auto IsClass = [](const TypeRef *TypeResult) {
+      // When the existential wraps a class type, LLDB expects that the
+      // address returned is the class instance itself and not the address
+      // of the reference.
+      bool IsClass = TypeResult->getKind() == TypeRefKind::ForeignClass ||
+                     TypeResult->getKind() == TypeRefKind::ObjCClass;
+      if (auto *nominal = llvm::dyn_cast<NominalTypeRef>(TypeResult))
+        IsClass = nominal->isClass();
+      else if (auto *boundGeneric =
+                   llvm::dyn_cast<BoundGenericTypeRef>(TypeResult))
+        IsClass = boundGeneric->isClass();
+      return IsClass;
+    };
+
+    auto DereferenceAndSet = [&](RemoteAddress &Address) {
+      auto PointerValue = readResolvedPointerValue(Address.getAddressData());
+      if (!PointerValue)
+        return false;
+      Address = RemoteAddress(*PointerValue);
+      return true;
+    };
+
+    auto ExistentialRecordTI = getRecordTypeInfo(&ExistentialTR, nullptr);
+    if (!ExistentialRecordTI)
+      return {};
+
+    switch (ExistentialRecordTI->getRecordKind()) {
+    case RecordKind::ClassExistential:
+      return getDynamicTypeAndAddressClassExistential(ExistentialAddress);
+    case RecordKind::ErrorExistential: {
+      // LLDB stores the address of the error pointer.
+      if (!DereferenceAndSet(ExistentialAddress))
+        return {};
+
+      bool IsBridgedError = false;
+      auto Pair = getDynamicTypeAndAddressErrorExistential(ExistentialAddress,
+                                                           &IsBridgedError);
+      if (!Pair)
+        return {};
+
+      if (!IsBridgedError && IsClass(std::get<const TypeRef *>(*Pair)))
+        if (!DereferenceAndSet(std::get<RemoteAddress>(*Pair)))
+          return {};
+
+      return Pair;
+    }
+    case RecordKind::OpaqueExistential: {
+      auto Pair = getDynamicTypeAndAddressOpaqueExistential(ExistentialAddress);
+      if (!Pair)
+        return {};
+
+      if (IsClass(std::get<const TypeRef *>(*Pair)))
+        if (!DereferenceAndSet(std::get<RemoteAddress>(*Pair)))
+          return {};
+
+      return Pair;
+    }
+    default:
+      return {};
+    }
+  }
 
   /// Projects the value of an enum.
   ///
@@ -889,6 +1004,12 @@ class ReflectionContext
     }
   }
 
+  const RecordTypeInfo *getRecordTypeInfo(const TypeRef *TR,
+                              remote::TypeInfoProvider *ExternalTypeInfo) {
+    auto *TypeInfo = getTypeInfo(TR, ExternalTypeInfo);
+    return dyn_cast_or_null<const RecordTypeInfo>(TypeInfo);
+  }
+
   /// Iterate the protocol conformance cache tree rooted at NodePtr, calling
   /// Call with the type and protocol in each node.
   void iterateConformanceTree(StoredPointer NodePtr,

include/swift/SwiftRemoteMirror/SwiftRemoteMirror.h

@@ -247,6 +247,19 @@ int swift_reflection_projectExistential(SwiftReflectionContextRef ContextRef,
                                         swift_typeref_t *OutInstanceTypeRef,
                                         swift_addr_t *OutStartOfInstanceData);
 
+/// Like swift_reflection_projectExistential, with 2 differences:
+///
+/// - When dealing with an error existential, this version will dereference 
+///   the ExistentialAddress before proceeding.
+/// - After setting OutInstanceTypeRef and OutStartOfInstanceData this version
+///   may derefence and set OutStartOfInstanceData if OutInstanceTypeRef is a 
+///   class TypeRef.
+SWIFT_REMOTE_MIRROR_LINKAGE
+int swift_reflection_projectExistentialAndUnwrapClass(
+    SwiftReflectionContextRef ContextRef, swift_addr_t ExistentialAddress,
+    swift_typeref_t ExistentialTypeRef, swift_typeref_t *OutInstanceTypeRef,
+    swift_addr_t *OutStartOfInstanceData);
+
 /// Projects the value of an enum.
 ///
 /// Takes the address and typeref for an enum and determines the

stdlib/private/SwiftReflectionTest/SwiftReflectionTest.swift

@@ -17,6 +17,7 @@
 //===----------------------------------------------------------------------===//
 
 let RequestInstanceKind = "k"
+let RequestShouldUnwrapClassExistential = "u"
 let RequestInstanceAddress = "i"
 let RequestReflectionInfos = "r"
 let RequestImages = "m"
@@ -346,11 +347,15 @@ internal func sendPointerSize() {
 /// The parent sends a Done message to indicate that it's done
 /// looking at this instance. It will continue to ask for instances,
 /// so call doneReflecting() when you don't have any more instances.
-internal func reflect(instanceAddress: UInt, kind: InstanceKind) {
+internal func reflect(instanceAddress: UInt, 
+                      kind: InstanceKind, 
+                      shouldUnwrapClassExistential: Bool = false) {
   while let command = readLine(strippingNewline: true) {
     switch command {
     case String(validatingUTF8: RequestInstanceKind)!:
       sendValue(kind.rawValue)
+    case String(validatingUTF8: RequestShouldUnwrapClassExistential)!:
+      sendValue(shouldUnwrapClassExistential)
     case String(validatingUTF8: RequestInstanceAddress)!:
       sendValue(instanceAddress)
     case String(validatingUTF8: RequestReflectionInfos)!:
@@ -437,12 +442,18 @@ public func reflect(object: AnyObject) {
 /// The test doesn't care about the witness tables - we only care
 /// about what's in the buffer, so we always put these values into
 /// an Any existential.
-public func reflect<T>(any: T, kind: InstanceKind = .Existential) {
+///
+/// If shouldUnwrapClassExistential is set to true, this exercises 
+/// projectExistentialAndUnwrapClass instead of projectExistential.
+public func reflect<T>(any: T, kind: InstanceKind = .Existential, 
+    shouldUnwrapClassExistential: Bool = false) {
   let any: Any = any
   let anyPointer = UnsafeMutablePointer<Any>.allocate(capacity: MemoryLayout<Any>.size)
   anyPointer.initialize(to: any)
   let anyPointerValue = UInt(bitPattern: anyPointer)
-  reflect(instanceAddress: anyPointerValue, kind: kind)
+  reflect(instanceAddress: anyPointerValue, 
+          kind: kind, 
+          shouldUnwrapClassExistential: shouldUnwrapClassExistential)
   anyPointer.deallocate()
 }
 
@@ -474,6 +485,21 @@ public func reflect<T: Error>(error: T) {
   reflect(instanceAddress: errorPointerValue, kind: .ErrorExistential)
 }
 
+// Like reflect<T: Error>(error: T), but calls projectExistentialAndUnwrapClass 
+// instead of projectExistential and adds an extra level of indirection, which is
+// what projectExistentialAndUnwrapClass expects.
+public func reflectUnwrappingClassExistential<T: Error>(error: T) {
+  let error: Error = error
+  let errorPointerValue = unsafeBitCast(error, to: UInt.self)
+  let anyPointer = UnsafeMutablePointer<Any>.allocate(capacity: MemoryLayout<Any>.size)
+  anyPointer.initialize(to: errorPointerValue)
+  let anyPointerValue = UInt(bitPattern: anyPointer)
+  reflect(instanceAddress: anyPointerValue, 
+          kind: .ErrorExistential, 
+          shouldUnwrapClassExistential: true)
+  anyPointer.deallocate()
+}
+
 // Reflect an `Enum`
 //
 // These are handled like existentials, but

stdlib/public/SwiftRemoteMirror/SwiftRemoteMirror.cpp

@@ -571,6 +571,23 @@ int swift_reflection_projectExistential(SwiftReflectionContextRef ContextRef,
   return Success;
 }
 
+int swift_reflection_projectExistentialAndUnwrapClass(SwiftReflectionContextRef ContextRef,
+                                        swift_addr_t ExistentialAddress,
+                                        swift_typeref_t ExistentialTypeRef,
+                                        swift_typeref_t *InstanceTypeRef,
+                                        swift_addr_t *StartOfInstanceData) {
+  auto Context = ContextRef->nativeContext;
+  auto ExistentialTR = reinterpret_cast<const TypeRef *>(ExistentialTypeRef);
+  auto RemoteExistentialAddress = RemoteAddress(ExistentialAddress);
+  auto Pair = Context->projectExistentialAndUnwrapClass(
+      RemoteExistentialAddress, *ExistentialTR);
+  if (!Pair.hasValue())
+    return false;
+  *InstanceTypeRef = reinterpret_cast<swift_typeref_t>(std::get<const TypeRef *>(*Pair));
+  *StartOfInstanceData = std::get<RemoteAddress>(*Pair).getAddressData();
+
+  return true;
+}
 int swift_reflection_projectEnumValue(SwiftReflectionContextRef ContextRef,
                                       swift_addr_t EnumAddress,
                                       swift_typeref_t EnumTypeRef,
@@ -761,4 +778,4 @@ const char *swift_reflection_iterateAsyncTaskAllocations(
         Call(AllocationPtr, Count, ConvertedChunks.data(), ContextPtr);
       });
   return returnableCString(ContextRef, Error);
-}
+}

stdlib/tools/swift-reflection-test/messages.h

@@ -11,6 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 static const char *REQUEST_INSTANCE_KIND = "k\n";
+static const char *REQUEST_SHOULD_UNWRAP_CLASS_EXISTENTIAL = "u\n";
 static const char *REQUEST_INSTANCE_ADDRESS = "i\n";
 static const char *REQUEST_REFLECTION_INFO = "r\n";
 static const char *REQUEST_IMAGES = "m\n";