https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119525
Bug ID: 119525
Summary: ICE when using template alias parameter deduction on
alias for std::variant
Product: gcc
Version: 15.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: whiteredredcat at gmail dot com
Target Milestone: ---
Created attachment 60911
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=60911&action=edit
the requested report generated with -freport-bug
When compiling the code below in the file `test2.cpp` with the command `g++
--std=c++23 test2.cpp` the compiler suffers an internal compiler error.
```
#include <variant>
template<typename T>
using templated_varient = std::variant<T>;
int main() {
templated_varient meow = std::variant<int>(10);
return 0;
}
// vim: ts=2 sw=2
```
The compiler output to console is thus:
```
In file included from test2.cpp:1:
/home/plum/patches/gcc-compile/built/include/c++/15.0.1/variant: In
substitution of ‘template<class ... _Types> template<class _Tp, class> using
std::variant<_Types>::__accepted_type = std::variant<_Types>::__to_type<((long
unsigned int)__accepted_index<_Tp>)> [with _Tp = _Tp&&;
<template-parameter-2-2> = typename
std::enable_if<std::variant<T>::__not_self<_Tp&&>, void>::type; _Types = {T}]’:
test2.cpp:7:47: required from here
7 | templated_varient meow = std::variant<int>(10);
| ^
/home/plum/patches/gcc-compile/built/include/c++/15.0.1/variant:1462:43:
internal compiler error: Segmentation fault
1462 | using __accepted_type = __to_type<__accepted_index<_Tp>>;
| ^~~~~~~~~~~~~~~~~~~~
0x294365f internal_error(char const*, ...)
/home/plum/patches/gcc-compile/../gcc/gcc/diagnostic-global-context.cc:517
0x144d6af crash_signal
/home/plum/patches/gcc-compile/../gcc/gcc/toplev.cc:322
0xd118f1 tsubst_expr(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:20558
0xd126e8 tsubst_expr(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:20655
0xd1772d tsubst_expr(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:13002
0xd1772d tsubst_template_arg(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:13013
0xd1772d tsubst_template_arg(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:13001
0xd271f9 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:14230
0xd274f2 tsubst_template_args(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:14212
0xd0b8b2 tsubst(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:16836
0xd0c268 tsubst(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:16446
0xd1f33a tsubst_decl
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:15772
0xd2c0bd instantiate_template(tree_node*, tree_node*, int)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:22700
0xd2c7a3 instantiate_alias_template
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:22798
0xd0c2a0 instantiate_alias_template
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:22776
0xd0c2a0 tsubst(tree_node*, tree_node*, int, tree_node*)
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:16447
0xd1873f rewrite_tparm_list
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:30415
0xd3545b alias_ctad_tweaks
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:30944
0xcf5801 deduction_guides_for
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:31302
0xcf5eaf do_class_deduction
/home/plum/patches/gcc-compile/../gcc/gcc/cp/pt.cc:31472
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.
```
Attached is the preprocessed source as requested. My compiled gcc version is
`gcc (GCC) 15.0.1 20250326`. I previously reported this bug to the Arch Linux
tracker as it also exists in gcc 14, see here for details:
https://gitlab.archlinux.org/archlinux/packaging/packages/gcc/-/issues/22
There Toolybird independently confirms that this bug exists in GCC 15.
As for duplicate bugs, the closest I found was
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115412
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86961
Though both of these have the templated using statement inside a struct and
thus are potentially different.
If I write templated_varient<int> meow = std::variant<int>(10);` instead, the
file complies with no issues.
`clang++ --std=c++23 test2.cpp` compiles the original buggy file with no
complaints.
