Code builds without -Wall, but not with -Wall

[Cristian Morales Vega]

The following code

----------------------------------
#include <boost/safe_numerics/safe_integer.hpp>
#include <fmt/format.h>
#include <fmt/ostream.h>

template<typename Stored,
         Stored Min,
         Stored Max,
         typename P,
         typename E>
struct fmt::formatter<
    boost::safe_numerics::safe_base<
        Stored, Min, Max, P, E
    >
> : fmt::ostream_formatter
{
};

void test()
{
    fmt::print("{}", boost::safe_numerics::safe<int>{ 4 });
}
----------------------------------

, using fmt 9.1.0 and Boost 1.80, builds in Ubuntu 20.04, with the default gcc (9.4.0-1ubuntu1~20.04.1), when using "-std=gnu++17 -Os" but not when using "-std=gnu++17 -Os -Wall".

The problem also exists with g++-10 10.3.0-1ubuntu1~20.04.

[Julian Andres Klode (juliank)]

Bug is not reproducible in kinetic with packaged versions of fmt and boost and g++ 12.

Given library versions are not shipped in 20.04.