Formatting std::exception_ptr:s

[avikivity]

It would be nice if the library (and the Standard) supported formatting std::exception_ptr:s as part of fmt/std.h or <format>. Of course, anyone can implement a formatter, but if third-party libraries do this, they will eventually clash.

[vitaut]

As usual, a PR to add such formatter would be welcome.

[avikivity]

My implementation has

    try {
        std::rethrow_exception(eptr);
    } catch(...) {
        auto tp = abi::__cxa_current_exception_type();
    ...

Is using nonstandard constructs acceptable? Properly guarded.

[vitaut]

Is using nonstandard constructs acceptable?

If there are clear benefits then sure.