This is a "use case" issue to try to clarify and discuss a use case, and how it will be addressed.

Building a project for a target that is not available in the Rust distribution can be challenging currently. Some use tools like cargo-xbuild or xargo, or forking rust itself. One of the goals of "std-aware Cargo" is to make this process a little easier.

Many use cases for this are for no_std environments, and use .json target specifications to specify the environment.

Cargo already supports .json targets, and most of the work for supporting #2 should enable this for basic usage.

However, from a higher level this use case has some other issues:

• Building no_std binaries often require nightly-only features. (TODO: list which are important).
• The core library is not always maximally portable. It might be good to explore Standard library portability to figure out what needs there are to make it more portable.
• Bringing up std on a new platform that does not conform to an existing one can be difficult. This might be another area to explore how to lower the difficulty.