Proposed resolution:

This wording is relative to N5032.

1. Modify [meta.reflection.queries] as indicated:

   consteval info constant_of(info r);
   

   -7- Let R be a constant expression of type `info` such that R == r is `true`. If `r` represents an annotation, then let C be its underlying constant.

   -8- Effects: Equivalent to:

   if constexpr (is_annotation(R)) {
     return C;
   } else if constexpr (is_array_type(type_of(R))) {
     return reflect_constant_array([: R :]);
   } else if constexpr (is_function_type(type_of(R))) {
     return reflect_function([: R :]);
   } else {
     return reflect_constant([: R :]);
   }
   

   -9- Throws: `meta::exception` unless either `r` represents an annotation or [: R :] is a valid splice-expression ([expr.prim.splice]) that doesn't designate a template.

The `constant_of` specification in [meta.reflection.queries] p9 says:

Throws: `meta::exception` unless either `r` represents an annotation or [: R :] is a valid splice-expression ([expr.prim.splice]).

But if we have `[:^^X:]` where `X` is a template, the splice-expression is valid, but we should still throw, because `constant_of` on a template declaration makes no sense. Since we call `reflect_constant` on the splice as per:

if constexpr (is_annotation(R)) {
  return C;
} else if constexpr (is_array_type(type_of(R))) {
  return reflect_constant_array([: R :]);
} else if constexpr (is_function_type(type_of(R))) {
  return reflect_function([: R :]);
} else {
  return reflect_constant([: R :]);
}

the code would be ill-formed anyway, but it seems clearer to say something like:

Throws: `meta::exception` unless either `r` represents an annotation or [: R :] is a valid splice-expression that doesn't designate a template.