How about changing [lib] to [[lib]], to allow multiple library in a crate?

[alexcrichton]

@brson

I would be doubly-happier if the metadata for those subprojects could be inferred instead of typed explicitly.

This sounds like a fantastic idea!

@mitsuhiko

The main reason this comes up are macros I think, and there it's not quite clear what is to be gained from that being in a separate crate.

When you say macros, do you mean macro_rules! macros or plugins? Currently I don't believe macro_rules! requires a separate crate, and plugins require a separate crate for technical reasons (cross compilation).