[Bug c++/86959] Use of a variadic alias template unexpectedly breaks compilation

[Bug c++/86959] Use of a variadic alias template unexpectedly breaks compilation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86959

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
clang ICEs with -std=c++20 :).

GCC ICEs starting in GCC 9:
<source>: In substitution of 'template<class> template<class ... T> using Alias
= Outer< <template-parameter-1-1> >::Inner<T ...> [with T = {void};
<template-parameter-1-1> = void]':
<source>:18:38:   required from here
<source>:8:11: internal compiler error: in lookup_template_class_1, at
cp/pt.c:10185
    8 |     using Alias = Inner<T...>;
      |           ^~~~~
0x1dd5279 internal_error(char const*, ...)
        ???:0
0x74caf1 fancy_abort(char const*, int, char const*)
        ???:0
0x9c6efe lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ???:0
0x9b1d4d tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x9b1df7 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x9e8992 instantiate_template(tree_node*, tree_node*, int)
        ???:0
0x9b22a9 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x9c557d lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ???:0
0xa1e7fd finish_template_type(tree_node*, tree_node*, int)
        ???:0
0x97e6b5 c_parse_file()
        ???:0
0xb03782 c_common_parse_file()
        ???:0
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