[Accepted as a DR at the November, 2023 meeting.]

Subclause 11.5.1 [class.union.general] paragraph 6 describes how union member subobjects are implicitly created by certain assignment operations that assign to union members. However, this description does not appear to properly handle the case of an anonymous union appearing within a union:

  union A {
    int x;
    union {
     int y;
    };
  };
  void f() {
    A a = {.x = 1};
    a.y = 2;
  }

Here, the expectation is that the assignment to a.y starts the lifetime of the anonymous union member subobject within A and also the int member subobject of the anonymous union member subobject. But the algorithm for computing S(a.y) determines that it is {a.y} and does not include the anonymous union member subobject.