Proposed resolution:

This wording is relative to N4659.

1. Change [deque.modifiers] as indicated:

   iterator erase(const_iterator position);
   iterator erase(const_iterator first, const_iterator last);
   void pop_front();
   void pop_back();
   

   -4- Effects: […]

   -5- Complexity: The number of calls to the destructor of T is the same as the number of elements erased, but the number of calls to the assignment operator of T is no more than the lesser of the number of elements before the erased elements and the number of elements after the erased elements.

   -6- Throws: Nothing unless an exception is thrown by the copy constructor, move constructor, assignment operator, or move assignment operator of T.

[ 2017-07 Toronto Wed Issue Prioritization ]

Priority 0; Move to Ready

Most of the discussion of LWG 2853 applies, mutatis mutandis, to deque::erase. The relevant requirements table requires neither Copy/MoveInsertable nor Copy/MoveConstructible for the erase operations, so there's no way a copy/move constructor can safely be called.

And "assignment operator or move assignment operator" is just "assignment operator", since "move assignment operator" is just a species of "assignment operator".