[AST] Use Type::transformRec() when getting a canonical type in context.

NFC cleanup

Author: DougGregor

lib/AST/GenericSignature.cpp

@@ -605,21 +605,22 @@ CanType GenericSignature::getCanonicalTypeInContext(Type type,
     return CanType(type);
 
   // Replace non-canonical type parameters.
-  type = type.transform([&](Type component) -> Type {
-    if (!component->isTypeParameter()) return component;
+  type = type.transformRec([&](TypeBase *component) -> Optional<Type> {
+    if (!isa<GenericTypeParamType>(component) &&
+        !isa<DependentMemberType>(component))
+      return None;
 
     // Resolve the potential archetype.  This can be null in nested generic
     // types, which we can't immediately canonicalize.
-    auto pa = builder.resolveArchetype(component);
-    if (!pa) return component;
+    auto pa = builder.resolveArchetype(Type(component));
+    if (!pa) return None;
 
     auto rep = pa->getArchetypeAnchor();
     if (rep->isConcreteType()) {
       return getCanonicalTypeInContext(rep->getConcreteType(), builder);
-    } else {
-      return rep->getDependentType(getGenericParams(),
-                                   /*allowUnresolved*/ false);
     }
+
+    return rep->getDependentType(getGenericParams(), /*allowUnresolved*/ false);
   });
 
   auto result = type->getCanonicalType();