Linker error not finding destructor when a function is templated

I have this weird bug which I cannot wrap my head around. I've reduced it to a simple example. I can fix it by creating an empty destructor, but I would really like to know what is going on.

#include <cstdio>
#include <functional>

struct test {
    inline test()
    {}

    const std::function<void()> f;
    const int universe = 42;
};

template<size_t n = 1>
inline void do_test(const test& t = {}) {
    printf("%d\n", t.universe);
}

int main(int, char**) {
//  test t;
    do_test();
    return 0;
}

This will not compile, outputting the error:

clang++ -O3 -std=c++1z -stdlib=libc++ -Wall main.cpp
Undefined symbols for architecture x86_64:
  "test::~test()", referenced from:
      _main in main-df96d9.o
ld: symbol(s) not found for architecture x86_64

If you either, uncomment the line where I create the test t; object, or remove the template parameter from do_test(), it will compile.

Note that the example is simplistic, the actual software requires the custom constructor, the template parameter, etc.

Any idea why it is complaining about finding the destructor?