Generalize extra inhabitants of tuples.

foo.swift

@@ -0,0 +1,25 @@
+
+enum SinglePayloadGenericEnumWithDefaultMirror<T, U> {
+  case Well
+  case Faucet
+  case Pipe(T, U)
+}
+
+func foo(x: Int, y: [Int], out: (SinglePayloadGenericEnumWithDefaultMirror<Int, [Int]>) -> ()) {
+  out(.Well)
+  out(.Faucet)
+  out(.Pipe(x, y))
+}
+
+func bar<T, U>(_ x: SinglePayloadGenericEnumWithDefaultMirror<T, U>) {
+  switch x {
+  case .Well:
+    print("well")
+  case .Faucet:
+    print("faucet")
+  case .Pipe:
+    print("pipe")
+  }
+}
+
+foo(x: 1, y: [1,2,3], out: bar)

include/swift/ABI/Metadata.h

@@ -1443,7 +1443,7 @@ struct TargetTupleTypeMetadata : public TargetMetadata<Runtime> {
   using StoredSize = typename Runtime::StoredSize;
   TargetTupleTypeMetadata() = default;
   constexpr TargetTupleTypeMetadata(const TargetMetadata<Runtime> &base,
-                                    StoredSize numElements,
+                                    uint32_t numElements,
                                     TargetPointer<Runtime, const char> labels)
     : TargetMetadata<Runtime>(base),
       NumElements(numElements),
@@ -1487,14 +1487,19 @@ struct TargetTupleTypeMetadata : public TargetMetadata<Runtime> {
     return getElements()[i];
   }
 
-  static constexpr StoredSize OffsetToNumElements = sizeof(TargetMetadata<Runtime>);
-
+  static constexpr StoredSize getOffsetToNumElements();
   static bool classof(const TargetMetadata<Runtime> *metadata) {
     return metadata->getKind() == MetadataKind::Tuple;
   }
 };
 using TupleTypeMetadata = TargetTupleTypeMetadata<InProcess>;
 
+template <typename Runtime>
+constexpr inline auto
+TargetTupleTypeMetadata<Runtime>::getOffsetToNumElements() -> StoredSize {
+  return offsetof(TargetTupleTypeMetadata<Runtime>, NumElements);
+}
+
 template <typename Runtime> struct TargetProtocolDescriptor;
 
 #if SWIFT_OBJC_INTEROP

include/swift/ABI/MetadataValues.h

@@ -244,7 +244,6 @@ class TargetExtraInhabitantFlags {
 
 public:
   constexpr TargetExtraInhabitantFlags() : Data(0) {}
-
   /// The number of extra inhabitants in the type's representation.
   int getNumExtraInhabitants() const { return Data & NumExtraInhabitantsMask; }
 

include/swift/Remote/MetadataReader.h

@@ -1087,8 +1087,8 @@ class MetadataReader {
         return _readMetadata<TargetStructMetadata>(address);
       case MetadataKind::Tuple: {
         auto numElementsAddress = address +
-          TargetTupleTypeMetadata<Runtime>::OffsetToNumElements;
-        StoredSize numElements;
+          TargetTupleTypeMetadata<Runtime>::getOffsetToNumElements();
+        uint32_t numElements;
         if (!Reader->readInteger(RemoteAddress(numElementsAddress),
                                  &numElements))
           return nullptr;