Description
From #402 (comment):
You can give the name of specific crates (separated with spaces I think). Rustc will then only allow unstable features for those crates. This could be used as a roadblock to prevent depending on unstable features outside of libcore, liballoc and libkernel. Driver code shouldn't ever rely on unstable features IMO. It is much easier to update only a few core crates than update many drivers as unstable features change.
This is blocked on allocator_api
(at least) becoming stable (or a way to e.g. enable some unstable features from the command line but not allowing any other in source code), but as soon as we can do it, it can be a very good idea, specially when we are in mainline where others will be writing Rust drivers independently of us.