I don't know of one, but you seemed to doubt not that it's actively being done, but that it's even possible, which is a very different proposition.

Remember C++ actually implements checks at compile time for the modern std::format function. That is, if you mess up the text of a format string so that it's invalid, C++ gives you a compile time error saying nope, that's not a valid format.

You might think that's just compiler magic, as it is for say printf-style formats in C, but nope, works for custom formats too, it's (extremely hairy) compile time executed C++.