WTF c++ ?

test.cc

#include <chrono>
#include <ctime>
#include <iostream>
#include <thread>


template <auto f>
constexpr auto foo() {
    return f();
}


auto bar() {
    return std::time(nullptr);
}


int main() {
    std::cout << foo<bar>() << std::endl;
    std::this_thread::sleep_for(std::chrono::seconds(2));
    std::cout << foo<bar>() << std::endl;
}