rusqlite: making a vtab loadable via sqlite3 (https://blog.davidvassallo.me/?p=4083)

vtab_2.rs

#[allow(clippy::not_unsafe_ptr_arg_deref)]
#[no_mangle]
pub extern "C" fn sqlite3_extension_init(
    db: *mut ffi::sqlite3,
    pz_err_msg: *mut *mut c_char,
    p_api: *mut ffi::sqlite3_api_routines,
) -> c_int {
    if p_api.is_null() {
        return ffi::SQLITE_ERROR;
    } else if let Err(err) = extension_init(db, p_api) {  // we handoff to `extenstion_init`
        return unsafe { to_sqlite_error(&err, pz_err_msg) };
    }
    ffi::SQLITE_OK
}

fn extension_init(db: *mut ffi::sqlite3, p_api: *mut ffi::sqlite3_api_routines) -> Result<()> {
    let db = unsafe { Connection::extension_init2(db, p_api)? };

    let module = rusqlite::vtab::eponymous_only_module::<Test>();
    db.create_module::<Test>("test", module, None)?;
    
    rusqlite::trace::log(ffi::SQLITE_WARNING, "Rusqlite extension initialized");
    Ok(())
}