`info` command, similar to GHCi

[murarth]

The command would resolve a name and print its type (for a named value) or definition (for a named type) and the place it was defined.

I don't think this is possible without a change to rustc. Resolution is performed by a rustc_resolve::Resolver instance, but the type is private and the name resolution data is dropped after it serves its purpose. CrateAnalysis uses NodeId as keys rather than names.