Drive-by fix for #132061 (comment)

Author: zyn0217

clang/lib/Sema/SemaTemplateDeductionGuide.cpp

@@ -972,6 +972,19 @@ getRHSTemplateDeclAndArgs(Sema &SemaRef, TypeAliasTemplateDecl *AliasTemplate) {
   return {Template, AliasRhsTemplateArgs};
 }
 
+bool IsNonDeducedArgument(const TemplateArgument &TA) {
+  // The following cases indicate the template argument is non-deducible:
+  //   1. The result is null. E.g. When it comes from a default template
+  //   argument that doesn't appear in the alias declaration.
+  //   2. The template parameter is a pack and that cannot be deduced from
+  //   the arguments within the alias declaration.
+  // Non-deducible template parameters will persist in the transformed
+  // deduction guide.
+  return TA.isNull() ||
+         (TA.getKind() == TemplateArgument::Pack &&
+          llvm::any_of(TA.pack_elements(), IsNonDeducedArgument));
+}
+
 // Build deduction guides for a type alias template from the given underlying
 // deduction guide F.
 FunctionTemplateDecl *