[dcl.attr.deprecated] Deprecating structured binding declarations

[cor3ntin]

[dcl.attr.deprecated]

Issue description:

The following code seem somewhat sensible, and there does not seem to be a a good reason for it to be disallowed

namespace binding {
  struct S { int i; }
  auto [G [[deprecated]]] = S{42};
  int test() {
    return G; // warn
  }
}

Suggested resolution:

The proposed warning mirror that of [[maybe_unused]]

Edit [dcl.attr.deprecated]/p2

The attribute may be applied to the declaration of a class, a typedef-name, a variable (including a structured binding declaration), a non-static data member, a function, a namespace, an enumeration, an enumerator, a concept, or a template specialization.

PS: The wording seemingly allows deprecating local variables, which seems of questionable usefulness.

[jensmaurer]

This a (small) feature request, and thus needs a paper to EWG. I believe there is no doubt the status quo wording in the Working Draft is clear that this is ill-formed.

And the wording doesn't do what you want it to do; the "variable" here refers to the hidden variable that is declared by a structured binding declaration, where G refers to a subobject of that variable.