[Bug c++/65071] New: ICE on valid, sizeof...() of template template parameter pack in return type

[maltsevm at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65071

            Bug ID: 65071
           Summary: ICE on valid, sizeof...() of template template
                    parameter pack in return type
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: maltsevm at gmail dot com

The following (presumably valid) code causes segfault on trunk r220715 and
4.9.2:

$ cat ./ice_sizeof.cc
template<int N>
struct array
{
    int data[N];
};

template<template<typename> class... T1, typename T2>
array<sizeof...(T1)> make_array(T1<T2> ...init)
{
    return { 0 };
}

template<typename T>
struct S
{
    T a;
};

auto arr = make_array(S<int>{1});

======================================================

miyuki@gcc-devel2:~/gcc/test/ice_sizeof$ ../../obj/gcc/cc1plus -std=c++11
ice_sizeof.cc &> bug_report.txt; cat bug_report.txt
 array<sizeof... (T1)> make_array(T1<T2>...) array<sizeof... (T1)>
make_array(T1<T2>...) [with T1 = {S}; T2 = int] void
__static_initialization_and_destruction_0(int, int) void _GLOBAL__sub_I_arr()
Analyzing compilation unit

ice_sizeof.cc: In instantiation of 'array<sizeof... (T1)> make_array(T1<T2>...)
[with T1 = {S}; T2 = int]':

ice_sizeof.cc:8:22: internal compiler error: tree check: expected class 'type',
have 'declaration' (template_decl) in write_CV_qualifiers_for_type, at
cp/mangle.c:2154
 array<sizeof...(T1)> make_array(T1<T2> ...init)
                      ^
0xefd737 tree_class_check_failed(tree_node const*, tree_code_class, char
const*, int, char const*)
        /home/miyuki/gcc/src/gcc/tree.c:9341
0x7c9e9b tree_class_check(tree_node*, tree_code_class, char const*, int, char
const*)
        /home/miyuki/gcc/src/gcc/tree.h:2969
0x7c9e9b write_CV_qualifiers_for_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:2154
0x7d03b3 write_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:1876
0x7d07e1 write_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:2049
0x7cf5b8 write_template_arg
        /home/miyuki/gcc/src/gcc/cp/mangle.c:3158
0x7cfcb8 write_template_args
        /home/miyuki/gcc/src/gcc/cp/mangle.c:2546
0x7ced2a write_name
        /home/miyuki/gcc/src/gcc/cp/mangle.c:831
0x7d09e6 write_class_enum_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:2517
0x7d09e6 write_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:1974
0x7d2d04 write_bare_function_type
        /home/miyuki/gcc/src/gcc/cp/mangle.c:2440
0x7d7b39 mangle_decl_string
        /home/miyuki/gcc/src/gcc/cp/mangle.c:3411
0x7d7d77 get_mangled_id
        /home/miyuki/gcc/src/gcc/cp/mangle.c:3433
0x7d7d77 mangle_decl(tree_node*)
        /home/miyuki/gcc/src/gcc/cp/mangle.c:3478
0xefdd10 decl_assembler_name(tree_node*)
        /home/miyuki/gcc/src/gcc/tree.c:697
0x910d77 symtab_node::get_comdat_group_id()
        /home/miyuki/gcc/src/gcc/cgraph.h:207
0x910d77 analyze_functions
        /home/miyuki/gcc/src/gcc/cgraphunit.c:973
0x9120e5 symbol_table::finalize_compilation_unit()
        /home/miyuki/gcc/src/gcc/cgraphunit.c:2427
0x6f3037 cp_write_global_declarations()
        /home/miyuki/gcc/src/gcc/cp/decl2.c:4750
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.

======================================================

GCC 4.9.2 20141030 (Red Hat 4.9.2-5.ac1), i386, also crashes.

GCC 4.8.2 20140120 (Red Hat 4.8.2-16) rejects the code with the following
error:
./ice_sizeof.cc:8:20: error: template argument 1 is invalid
 array<sizeof...(T1)> make_array(T1<T2> ...init)

clang-3.7 compiles the file without errors.

Changing the declaration to
"auto make_array_ice(T1<T2> ...init) -> array<sizeof...(T1)>"
does not change the behavior, but
"auto make_array_ice(T1<T2> ...init) -> array<sizeof...(init)>"
gets compiled without errors by all 3 mentioned versions of g++.