[Bug c++/86986] New: Unexpected errors for template parameter pack in a template template parameter

[v.reshetnikov at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86986

            Bug ID: 86986
           Summary: Unexpected errors for template parameter pack in a
                    template template parameter
           Product: gcc
           Version: 9.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: v.reshetnikov at gmail dot com
  Target Milestone: ---

/************* SOURCE *************/
template<class... T>
struct X {
    template<template<T...> class...>
    struct Y { };
};

using type = X<int>::Y<>;
/*********** END SOURCE ***********/


/************* OUTPUT *************/
<source>: In instantiation of 'struct X<int>':
<source>:7:20:   required from here
<source>:4:12: error: '<template-parameter-1-1>' is not a valid type for a
template non-type parameter
4 |     struct Y { };
  |            ^
<source>:4:12: error: '<template-parameter-1-1>' is not a valid type for a
template non-type parameter
<source>:7:22: error: 'Y' in 'struct X<int>' does not name a template type
7 | using type = X<int>::Y<>;
  |                      ^
Compiler returned: 1
/*********** END OUTPUT ***********/

Clang compiles this code successfully