[Bug c++/91793] [8/9/trunk regression] ICE on unexpanded parameter pack in lambda

[cyp561 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91793

--- Comment #2 from Cyp <cyp561 at gmail dot com> ---
Compiler output from reduced testcase:
-------------------
91793.cpp: In instantiation of ‘<lambda(auto:1 ...)> [with auto:1 = {}]’:
91793.cpp:6:4:   required from here
91793.cpp:4:25: internal compiler error: Segmentation fault
    using b = decltype(a);
                         ^
0xb61e5f crash_signal
        /var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/toplev.c:325
0x7f1b8e9f202f ???
       
/var/tmp/portage/sys-libs/glibc-2.29-r2/work/glibc-2.29/signal/../sysdeps/unix/sysv/linux/x86_64/sigaction.c:0
0x70ea21 invalid_nonstatic_memfn_p(unsigned int, tree_node*, int)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/typeck.c:1887
0x6f546a finish_decltype_type(tree_node*, bool, int)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/semantics.c:8769
0x6c5661 tsubst(tree_node*, tree_node*, int, tree_node*)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:14982
0x6d6734 tsubst_decl
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:13704
0x6c5d5f tsubst(tree_node*, tree_node*, int, tree_node*)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:14217
0x6c2b31 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16707
0x6c17ae tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16930
0x6c17ae tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16930
0x6d7578 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16615
0x6d7578 tsubst_lambda_expr(tree_node*, tree_node*, int, tree_node*)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:17685
0x6cee41 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:18971
0x6c22d4 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:17446
0x6c2098 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16644
0x6c18e6 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16630
0x6c17ae tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16930
0x6c17ae tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16930
0x6c03a3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:16615
0x6c03a3 instantiate_decl(tree_node*, bool, bool)
       
/var/tmp/portage/sys-devel/gcc-8.3.0-r1/work/gcc-8.3.0/gcc/cp/pt.c:24066
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://bugs.gentoo.org/> for instructions.