[Bug c++/71837] New: ICE on valid C++14 code with initialized lambda capture: in tsubst_pack_expansion, at cp/pt.c:10905

[su at cs dot ucdavis.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71837

            Bug ID: 71837
           Summary: ICE on valid C++14 code with initialized lambda
                    capture: in tsubst_pack_expansion, at cp/pt.c:10905
           Product: gcc
           Version: 7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: su at cs dot ucdavis.edu
  Target Milestone: ---

The following C++14 code causes an ICE when compiled with the current GCC trunk
on x86_64-linux-gnu in both 32-bit and 64-bit modes.  

It also affects at least 4.9.x, 5.x and 6.x. 

The code is accepted by both Clang and MSVC. 


$ g++-trunk -v
Using built-in specs.
COLLECT_GCC=g++-trunk
COLLECT_LTO_WRAPPER=/usr/local/gcc-trunk/libexec/gcc/x86_64-pc-linux-gnu/7.0.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: ../gcc-source-trunk/configure --enable-languages=c,c++,lto
--prefix=/usr/local/gcc-trunk --disable-bootstrap
Thread model: posix
gcc version 7.0.0 20160711 (experimental) [trunk revision 238202] (GCC)
$
$ clang++-3.8 -c -std=c++14 small.cpp
$
$ g++-trunk -c -std=c++14 small.cpp
small.cpp: In instantiation of ‘struct f(Ts ...) [with Ts = {int}]::<lambda>’:
small.cpp:3:22:   required from ‘void f(Ts ...) [with Ts = {int}]’
small.cpp:8:7:   required from here
small.cpp:3:16: error: invalid use of pack expansion expression
   [ts (args ...)] {} ();
                ^
small.cpp:3:16: internal compiler error: in tsubst_pack_expansion, at
cp/pt.c:10905
0x6f7d64 tsubst_pack_expansion(tree_node*, tree_node*, int, tree_node*)
        ../../gcc-source-trunk/gcc/cp/pt.c:10905
0x6e4920 tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:16780
0x71da10 instantiate_class_template_1
        ../../gcc-source-trunk/gcc/cp/pt.c:10359
0x71da10 instantiate_class_template(tree_node*)
        ../../gcc-source-trunk/gcc/cp/pt.c:10417
0x7c0973 complete_type(tree_node*)
        ../../gcc-source-trunk/gcc/cp/typeck.c:133
0x6e243c tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:17194
0x6e48aa tsubst_copy_and_build(tree_node*, tree_node*, int, tree_node*, bool,
bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:16536
0x6d6cbf tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:15868
0x6d735a tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:15180
0x6d66b3 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:15166
0x6d81f0 tsubst_expr(tree_node*, tree_node*, int, tree_node*, bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:15351
0x6d4bf5 instantiate_decl(tree_node*, int, bool)
        ../../gcc-source-trunk/gcc/cp/pt.c:22095
0x7218d2 instantiate_pending_templates(int)
        ../../gcc-source-trunk/gcc/cp/pt.c:22214
0x764a05 c_parse_final_cleanups()
        ../../gcc-source-trunk/gcc/cp/decl2.c:4600
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <http://gcc.gnu.org/bugs.html> for instructions.
$


----------------------------------------------------


template < typename ... Ts > void f (Ts ... args)
{ 
  [ts (args ...)] {} ();
}

int main ()
{ 
  f (0);
  return 0;
}