Full name of submitter: Brian Bi

Issue description: There is a gap in the specification of composite pointer type if both a pointer-to-member conversion and a qualification conversion are needed to achieve a common type. However, all implementations accept at least some such cases.

using P = int*;
using CP = const int* const;
struct B {
    P a;
};
struct D : B {};

constexpr P (B::*bnc) = &B::a;
constexpr CP (B::*bc) = &B::a;
constexpr P (D::*dnc) = &B::a;
constexpr CP (D::*dc) = dnc;  // work around GCC bug

static_assert(bnc == dc);
static_assert(bc == dnc);  // EDG rejects

Suggested resolution: Edit [expr.type]/3.7 and add sub-bullets as follows. Note that the cross-reference to [dcl.init.ref] is struck because it already occurs in an earlier bullet.

• if T1 is “pointer to member of C1 of type cv1 U1” and T2 is “pointer to member of C2 of type cv2 U2”, for some non-function type U, where

  • U1 and U2 are similar object types and
  • C1 is reference-related to C2 or C2 is reference-related to C1 ([dcl.init.ref]),

  the qualification-combined type of T2 and T1 or the qualification-combined type of T1 and T2, respectively;