[Moved to DR at the November, 2014 meeting.]

Proposed resolution (February, 2014):

Change the grammar in 7.6.1 [expr.post] paragraph 1 as follows:

pseudo-destructor-name:
nested-name-specifier_opt type-name :: ~ type-name
nested-name-specifier template simple-template-id :: ~ type-name
nested-name-specifier_opt ~ type-name
~ decltype-specifier

One of the forms of pseudo-destructor-name is

nested-name-specifier_opt ~ type-name

Presumably the intent of this form is to allow the nested-name-specifier to designate a namespace; otherwise the

nested-name-specifier_opt type-name :: ~ type-name

production would be used.

Since one of the forms of nested-name-specifier is

decltype-specifier ::

one can write something like p->decltype(x)::~Y(). However, the lookup rules in 6.5.5 [basic.lookup.qual] paragraph 6 are inappropriate for the decltype-specifier case:

If a pseudo-destructor-name (_N4778_.7.6.1.4 [expr.pseudo]) contains a nested-name-specifier, the type-names are looked up as types in the scope designated by the nested-name-specifier.

Since this form appears to be useless (use of a decltype-specifier is permitted after a ~, but only with no nested-name-specifer — but see issue 1586), perhaps it should be made ill-formed.