(From submission #743.)

Consider:

struct S { };
void f() {
  S s;
  template for (auto x : s) { }
}

This destructuring expansion statement is ill-formed, because the syntactic rewrite contains

  auto&& [] = s ;

which is an ill-formed structured binding declaration.

Empty expansion statements are allowed for the other two kinds of expansion statements.

Possible resolution:

Change in 8.7 [stmt.expand] bullet 5.3 as follows:

• Otherwise, S is a destructuring expansion statement and, if N is 0, S is equivalent to:

  init-statement
  constexpropt auto&& range = expansion-initializer ;
  

  otherwise, S is equivalent to: ...