Originally reported on Community Hub release announcement:

When trying to update from 4.1.4 to 4.3.0, compilations failed due to lack of RTTI:

../../../../../../../../../../objectbox/src/main/cpp/external/mongo-cxx-driver/src/mongocxx/lib/mongocxx/v_noabi/mongocxx/mongoc_error.hh:111:26: error: use of dynamic_cast requires -frtti
 111 | if (auto const ptr = dynamic_cast<v1::server_error const*>(&ex)) {
 | ^
1 error generated.

Is using dynamic_cast an oversight there, or is RTTI now required?
Is using dynamic_cast an oversight there, or is RTTI now required?

P.S.: To clarify, we disable RTTI in some configurations and it has worked without in mongocxx for many versions.

This is the commit: https://github.com/mongodb/mongo-cxx-driver/commit/82f77b60b9d134c1104272727c0e2bee51beb0ca

And looking at the code in question, it seems to be some kind of exception mapping:

template <typename exception_type>
[[noreturn]] void throw_exception(v1::exception const& ex) {
    if (auto const ptr = dynamic_cast<v1::server_error const*>(&ex)) {
        throw exception_type{
            ptr->code(), bsoncxx::v_noabi::document::value{bsoncxx::v_noabi::from_v1(ptr->raw())}, ptr->what()};
    }

    throw exception_type{ex.code(), ex.what()};
}

Maybe the dynamic cast could be avoided by overloading with a v1::server_error parameter - if callers still have the full type info.

Also, just for my personal curiosity, why does this exception mapping happen in the first place?