[AST] Fail an assertion when printing a TypeVariableType with an unknown originator

Author: ahoppen

lib/AST/ASTDumper.cpp

@@ -3766,8 +3766,10 @@ namespace {
         printFlag("error_expr");
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         printRec("dependent_member_type", DMT);
-      } else {
+      } else if (originator.is<PlaceholderTypeRepr *>()) {
         printFlag("placeholder_type_repr");
+      } else {
+        assert(false && "unknown originator");
       }
       PrintWithColorRAII(OS, ParenthesisColor) << ')';
     }

lib/AST/ASTPrinter.cpp

@@ -5701,8 +5701,10 @@ class TypePrinter : public TypeVisitor<TypePrinter> {
         Printer << "error_expr";
       } else if (auto *DMT = originator.dyn_cast<DependentMemberType *>()) {
         visit(DMT);
-      } else {
+      } else if (originator.is<PlaceholderTypeRepr *>()) {
         Printer << "placeholder_type_repr";
+      } else {
+        assert(false && "unknown originator");
       }
       Printer << ">>";
     } else {