AST: Use TypeTransform::transformDependentMember() to transform DependentMemberType

Author: slavapestov

include/swift/AST/TypeTransform.h

@@ -658,17 +658,7 @@ case TypeKind::Id:
 
     case TypeKind::DependentMember: {
       auto dependent = cast<DependentMemberType>(base);
-      auto dependentBase = doIt(dependent->getBase(), pos);
-      if (!dependentBase)
-        return Type();
-
-      if (dependentBase.getPointer() == dependent->getBase().getPointer())
-        return t;
-
-      if (auto assocType = dependent->getAssocType())
-        return DependentMemberType::get(dependentBase, assocType);
-
-      return DependentMemberType::get(dependentBase, dependent->getName());
+      return asDerived().transformDependentMember(dependent, pos);
     }
 
     case TypeKind::GenericFunction:
@@ -1004,6 +994,20 @@ case TypeKind::Id:
 
     return PackElementType::get(transformedPack, element->getLevel());
   }
+
+  Type transformDependentMember(DependentMemberType *dependent, TypePosition pos) {
+    auto dependentBase = doIt(dependent->getBase(), pos);
+    if (!dependentBase)
+      return Type();
+
+    if (dependentBase.getPointer() == dependent->getBase().getPointer())
+      return dependent;
+
+    if (auto assocType = dependent->getAssocType())
+      return DependentMemberType::get(dependentBase, assocType);
+
+    return DependentMemberType::get(dependentBase, dependent->getName());
+  }
 };
 
 }

lib/AST/TypeSubstitution.cpp

@@ -494,6 +494,8 @@ class TypeSubstituter : public TypeTransform<TypeSubstituter> {
 
   Type transformPackElement(PackElementType *element, TypePosition pos);
 
+  Type transformDependentMember(DependentMemberType *dependent, TypePosition pos);
+
   SubstitutionMap transformSubstitutionMap(SubstitutionMap subs);
 
   CanType transformSILField(CanType fieldTy, TypePosition pos);
@@ -510,19 +512,6 @@ TypeSubstituter::transform(TypeBase *type, TypePosition position) {
          "should not be doing AST type-substitution on a lowered SIL type;"
          "use SILType::subst");
 
-  // We only substitute for substitutable types and dependent member types.
-  
-  // For dependent member types, we may need to look up the member if the
-  // base is resolved to a non-dependent type.
-  if (auto depMemTy = dyn_cast<DependentMemberType>(type)) {
-    auto newBase = doIt(depMemTy->getBase(), TypePosition::Invariant);
-    return getMemberForBaseType(IFS,
-                                depMemTy->getBase(), newBase,
-                                depMemTy->getAssocType(),
-                                depMemTy->getName(),
-                                level);
-  }
-  
   auto substOrig = dyn_cast<SubstitutableType>(type);
   if (!substOrig)
     return std::nullopt;
@@ -593,6 +582,16 @@ Type TypeSubstituter::transformPackElement(PackElementType *element,
   return doIt(element->getPackType(), pos);
 }
 
+Type TypeSubstituter::transformDependentMember(DependentMemberType *dependent,
+                                               TypePosition pos) {
+  auto newBase = doIt(dependent->getBase(), TypePosition::Invariant);
+  return getMemberForBaseType(IFS,
+                              dependent->getBase(), newBase,
+                              dependent->getAssocType(),
+                              dependent->getName(),
+                              level);
+}
+
 SubstitutionMap TypeSubstituter::transformSubstitutionMap(SubstitutionMap subs) {
   // FIXME: Take level into account? Move level down into IFS?
   return subs.subst(IFS);