AST: Introduce PackArchetypeType::getSingletonPackType()

Author: slavapestov

include/swift/AST/Types.h

@@ -6054,6 +6054,8 @@ class PackArchetypeType final
     return T->getKind() == TypeKind::PackArchetype;
   }
 
+  CanTypeWrapper<PackType> getSingletonPackType();
+
 private:
   PackArchetypeType(const ASTContext &Ctx, GenericEnvironment *GenericEnv,
                     Type InterfaceType, ArrayRef<ProtocolDecl *> ConformsTo,

lib/AST/ParameterPack.cpp

@@ -418,4 +418,11 @@ PackType *PackType::get(const ASTContext &C,
   }
 
   return get(C, wrappedArgs)->flattenPackTypes();
-}
+}
+
+
+CanPackType PackArchetypeType::getSingletonPackType() {
+  SmallVector<Type, 1> types;
+  types.push_back(PackExpansionType::get(this, getReducedShape()));
+  return CanPackType(PackType::get(getASTContext(), types));
+}

lib/IRGen/GenType.cpp

@@ -2215,15 +2215,12 @@ const TypeInfo *TypeConverter::convertType(CanType ty) {
   case TypeKind::Pack:
     return convertPackType(cast<PackType>(ty));
   case TypeKind::PackArchetype: {
-    // FIXME: This is the wrong place for this kind of wrapping
-    SmallVector<Type> elts;
     auto archetypeTy = cast<PackArchetypeType>(ty);
-    elts.push_back(PackExpansionType::get(archetypeTy,
-                                          archetypeTy->getReducedShape()));
-    return convertPackType(PackType::get(IGM.Context, elts));
+    return convertPackType(archetypeTy->getSingletonPackType());
   }
   case TypeKind::PackExpansion: {
-    // FIXME: This is the wrong place for this kind of wrapping
+    // FIXME: SIL shouldn't emit values with pack expansion type; they
+    // should always be wrapped in a PackType or be a bare PackArchetypeType
     SmallVector<Type> elts;
     elts.push_back(ty);
     return convertPackType(PackType::get(IGM.Context, elts));