[Bug c++/106351] New: ICE in fold expression involving templatized lambda

["amir.ahmed.ansari at outlook dot com" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106351

            Bug ID: 106351
           Summary: ICE in fold expression involving templatized lambda
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: amir.ahmed.ansari at outlook dot com
  Target Milestone: ---

The following code:

template <typename ...Args>
struct C
{
    void f()
    {
        (
            [&, this]<typename Arg>()
            {
            }.operator()<Args>(),
            ...
        );
    }
};

int main()
{
    C<int>{}.f();

    return 0;
}

produces:

<source>: In instantiation of 'void C<Args>::f() [with Args = {int}]':
<source>:17:15:   required from here
<source>:9:30: internal compiler error: in lookup_template_class_1, at
cp/pt.cc:10114
    7 |             [&, this]<typename Arg>()
      |             ~~~~~~~~~~~~~~~~~~~~~~~~~
    8 |             {
      |             ~                 
    9 |             }.operator()<Args>(),
      |             ~~~~~~~~~~~~~~~~~^
0x1ba65f9 internal_error(char const*, ...)
        ???:0
0x6fad32 fancy_abort(char const*, int, char const*)
        ???:0
0x87f6fd lookup_template_class(tree_node*, tree_node*, tree_node*, tree_node*,
int, int)
        ???:0
0x875d31 tsubst(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x881224 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
        ???:0
0x878889 instantiate_decl(tree_node*, bool, bool)
        ???:0
0x8936ab instantiate_pending_templates(int)
        ???:0
0x79c46d c_parse_final_cleanups()
        ???:0
Please submit a full bug report, with preprocessed source (by using
-freport-bug).
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.
ASM generation compiler returned: 1