Macro rubbl_core::rn_warning

macro_rules! rn_warning {
    ($dest:expr, $( $fmt_args:expr ),*) => { ... };
    ($dest:expr, $( $fmt_args:expr ),* ; $err:expr) => { ... };
}

Warn the user of a problematic condition.

See the documentation of rn_note! for usage information. This macro should be used when an unusual condition has been detected, but the task at hand will likely succeed.