Package and Target are two important internal datastructures in Cargo, and we expose them for tools via various JSON messages.

To refer to a pacakge, we use an opaque in theory PackageId string. We don't have an obvious way to refer to a target of a package, and that I think causes problems.

Specifically, I think we have three places which would like to refer to targets, and each does it in its own way:

• In Artifact, we refer to target by just printing the whole target
• In cargo metadata, we don't refer to targets from resolve deps at all, but we probably should
• In the build plan PR, we print TargetKind, which is ambiguous.

Possible solution

• Just use the whole target as in Artifact, everywhere (on the one hand, this seems kind-of inelegant and duplicate, on the other hand, this is simple and straightforward)

• Use path to root file as a target_id, or (if that's ambigious), a pair of kind, path