https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114994
Bug ID: 114994
Summary: fmtlib named argument compiler error introduced in
g++-14.1
Product: gcc
Version: 14.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: andrew.corrigan at gmail dot com
Target Milestone: ---
Demo: https://godbolt.org/z/oachhYKcT
First reported to https://github.com/fmtlib/fmt/issues/3953. The fmtlib author
believes the error below is a compiler bug. Using fmtlib's named arguments
inside a generic lambda stopped working as of g++-14.1. The reproducer below
compiles on every other compiler I've tried (earlier versions of g++, clang++,
intel, and msvc)
```
#include <iostream>
#define FMT_HEADER_ONLY
#include <fmt/format.h>
using namespace fmt::literals;
int main()
{
auto test = [&](auto a)
{
return fmt::format("{foo} {bar}", "foo"_a="foo", "bar"_a="bar");
};
std::cout << test(1) << std::endl;
return 0;
}
```
Error:
```
<source>:12:50: error: cannot bind non-const lvalue reference of type
'fmt::v10::detail::named_arg<char, const char (&)[4]>&' to an rvalue of type
'fmt::v10::detail::named_arg<char, const char (&)[4]>'
12 | return fmt::format("{foo} {bar}", "foo"_a="foo",
"bar"_a="bar");
| ~~~~~~~^~~~~~
```
Changing `auto a` to `int a` works around the error.
Thank you!
