Add Extended Existential Vaulue Projection Utilities

Author: CodaFi

include/swift/ABI/Metadata.h

@@ -2125,6 +2125,16 @@ struct TargetExtendedExistentialTypeMetadata
     return this->template getTrailingObjects<ConstTargetPointer<Runtime, void>>();
   }
 
+public:
+  /// Project the value pointer from an extended existential container of the
+  /// type described by this metadata.
+  const OpaqueValue *projectValue(const OpaqueValue *container) const;
+
+  OpaqueValue *projectValue(OpaqueValue *container) const {
+    return const_cast<OpaqueValue *>(
+        projectValue((const OpaqueValue *)container));
+  }
+
 public:
   static bool classof(const TargetMetadata<Runtime> *metadata) {
     return metadata->getKind() == MetadataKind::ExtendedExistential;

include/swift/ABI/MetadataValues.h

@@ -899,6 +899,7 @@ class ExtendedExistentialTypeShapeFlags {
   SpecialKind getSpecialKind() const {
     return SpecialKind((Data & SpecialKindMask) >> SpecialKindShift);
   }
+  bool isOpaque() const { return getSpecialKind() == SpecialKind::None; }
   bool isClassConstrained() const {
     return getSpecialKind() == SpecialKind::Class;
   }

stdlib/public/runtime/Metadata.cpp

@@ -3980,6 +3980,32 @@ ExistentialTypeMetadata::projectValue(const OpaqueValue *container) const {
       "Unhandled ExistentialTypeRepresentation in switch.");
 }
 
+template <>
+const OpaqueValue *ExtendedExistentialTypeMetadata::projectValue(
+    const OpaqueValue *container) const {
+  switch (Shape->Flags.getSpecialKind()) {
+  case ExtendedExistentialTypeShape::SpecialKind::None: {
+    auto *opaqueContainer =
+        reinterpret_cast<const OpaqueExistentialContainer *>(container);
+    return opaqueContainer->projectValue();
+  }
+  case ExtendedExistentialTypeShape::SpecialKind::Class: {
+    auto classContainer =
+        reinterpret_cast<const ClassExistentialContainer *>(container);
+    return reinterpret_cast<const OpaqueValue *>(&classContainer->Value);
+  }
+  case ExtendedExistentialTypeShape::SpecialKind::Metatype: {
+    auto *metatypeContainer =
+        reinterpret_cast<const ExistentialMetatypeContainer *>(container);
+    return reinterpret_cast<const OpaqueValue *>(&metatypeContainer->Value);
+  }
+  case ExtendedExistentialTypeShape::SpecialKind::ExplicitLayout:
+    swift_unreachable("ExplicitLayout not yet handled.");
+  }
+
+  swift_unreachable("Unhandled ExistentialTypeRepresentation in switch.");
+}
+
 template<> const Metadata *
 ExistentialTypeMetadata::getDynamicType(const OpaqueValue *container) const {
   switch (getRepresentation()) {