Ooo. I want to be able to do an expression in a format string.<p>Instead of:<p>format!("{}:{} wasn't able to connect to host {}.", file!(), line!(), db_opts.hostname);<p>I'd rather do:<p>format!("{file!()}:{line!()} wasn't able to connect to host {db_opts.hostname}.");<p>Yes, expressions in format strings can be abused, but knee-capping a pretty standard case (`instance.field`)to prevent outlier bad behavior seems like a premature optimization.