AST: Use TypeTransform::transformPackElement() to transform PackElementType

Author: slavapestov

include/swift/AST/TypeTransform.h

@@ -592,15 +592,7 @@ case TypeKind::Id:
 
     case TypeKind::PackElement: {
       auto element = cast<PackElementType>(base);
-
-      Type transformedPack = doIt(element->getPackType(), pos);
-      if (!transformedPack)
-        return Type();
-
-      if (transformedPack.getPointer() == element->getPackType().getPointer())
-        return t;
-
-      return PackElementType::get(transformedPack, element->getLevel());
+      return asDerived().transformPackElement(element, pos);
     }
 
     case TypeKind::Tuple: {
@@ -1001,6 +993,17 @@ case TypeKind::Id:
 
     return PackExpansionType::get(transformedPat, transformedCount);
   }
+
+  Type transformPackElement(PackElementType *element, TypePosition pos) {
+    Type transformedPack = doIt(element->getPackType(), pos);
+    if (!transformedPack)
+      return Type();
+
+    if (transformedPack.getPointer() == element->getPackType().getPointer())
+      return element;
+
+    return PackElementType::get(transformedPack, element->getLevel());
+  }
 };
 
 }

lib/AST/TypeSubstitution.cpp

@@ -492,6 +492,8 @@ class TypeSubstituter : public TypeTransform<TypeSubstituter> {
 
   Type transformPackExpansion(PackExpansionType *expand, TypePosition pos);
 
+  Type transformPackElement(PackElementType *element, TypePosition pos);
+
   SubstitutionMap transformSubstitutionMap(SubstitutionMap subs);
 
   CanType transformSILField(CanType fieldTy, TypePosition pos);
@@ -508,14 +510,6 @@ TypeSubstituter::transform(TypeBase *type, TypePosition position) {
          "should not be doing AST type-substitution on a lowered SIL type;"
          "use SILType::subst");
 
-  auto oldLevel = level;
-  SWIFT_DEFER { level = oldLevel; };
-
-  if (auto elementTy = dyn_cast<PackElementType>(type)) {
-    type = elementTy->getPackType().getPointer();
-    level += elementTy->getLevel();
-  }
-
   // We only substitute for substitutable types and dependent member types.
 
   // For dependent member types, we may need to look up the member if the
@@ -592,6 +586,13 @@ Type TypeSubstituter::transformPackExpansion(PackExpansionType *expand,
   return Type(PackType::get(expand->getASTContext(), eltTys));
 }
 
+Type TypeSubstituter::transformPackElement(PackElementType *element,
+                                           TypePosition pos) {
+  SWIFT_DEFER { level -= element->getLevel(); };
+  level += element->getLevel();
+  return doIt(element->getPackType(), pos);
+}
+
 SubstitutionMap TypeSubstituter::transformSubstitutionMap(SubstitutionMap subs) {
   // FIXME: Take level into account? Move level down into IFS?
   return subs.subst(IFS);