[Bug c++/85279] New: [6/7/8 Regression] Broken diagnostic for decltype

[reichelt at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=85279

            Bug ID: 85279
           Summary: [6/7/8 Regression] Broken diagnostic for decltype
           Product: gcc
           Version: 8.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: reichelt at gcc dot gnu.org
  Target Milestone: ---

The following invalid testcase produces a broken diagnostic since GCC 4.7.0:

====================================
template<typename T> struct A
{
  void foo(decltype(T())::Y);
};
====================================

bug.cc:3:27: error: '#'decltype_type' not supported by dump_expr#<expression
error>::Y' is not a type
   void foo(decltype(T())::Y);
                           ^