https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109168
Bug ID: 109168
Summary: bogus error: 'X' is not a valid template argument of
type 'Y' because 'X' is not a variable
Product: gcc
Version: 13.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: waffl3x at protonmail dot com
Target Milestone: ---
https://godbolt.org/z/5xxPhhno7
struct stores_fptr {
void (*fptr)();
};
void func() {}
struct holds_value {
static constexpr auto value = stores_fptr{&func};
};
template<stores_fptr V> struct takes_value {};
using go = takes_value<holds_value::value>;
There are a few workarounds for this that I could find, the most obvious being
the following changes (working example): https://godbolt.org/z/81xr36bYc
template<auto V> struct takes_value {};
inline constexpr auto f = holds_value::value.fptr;
using go = takes_value<f>;
I want to note, the bug is still present in the broken example if `takes_value`
takes a deduced (auto) non type template parameter, I explicitly state the type
just to reduce the example further.
The first (broken) snippit works in clang, and is broken in gcc trunk, gcc
12.2, and gcc 11.2, I was not able to test on MSVC. I'm mildly concerned that
this is one of those cases where clang is wrong to accept the code, but I was
able to find enough workarounds that I feel like I'm not incorrect.
The code also fails on my system with version: g++ (GCC) 13.0.1 20230219
(experimental)
Here is the gcc version on compiler explorer at the time of writing: g++
(Compiler-Explorer-Build-gcc-0c061da91a3657afdb3fac68e4595af685909a1a-binutils-2.38)
13.0.1 20230316 (experimental)
BTW, should I be selecting the oldest version that a bug occurs or the newest
version? I observed the behavior all the way back to 10.1, which appears to be
when support for C++20 starts. I guess the better question to ask is how do I
assign multiple versions?
