I'm not intimately familiar with the internals of rustc, but my impression was that everything gets compiled and dead code is later eliminated. In order to avoi

I'm not intimately familiar with the internals of rustc, but my impression was that everything gets compiled and dead code is later eliminated. In order to avoid compiling unnecessary stuff, you generally need to use feature flags (e.g. you can say "only compile this if the serialization feature is enabled").