resolving logic applied to building dependencies

Item for discussion;
Would be immensely useful (I feel) if packages that are being built, could be queried for the order which would allow their requirements to be built in the order required to ensure that dependencies of the next-to-build package are always satisfied.

As a next step, providing a mechanism to allow a package and/or rez-build command to specify another package build as a part of its build process would allow a chained dependent compilation with a single command, further leveraging rez' already extensively useful environment resolving logic.

I feel as though this could simply be logically possible by providing the rez-build command with a source directory (in which unbuilt packages are located) and the ability for a missing-package-failed-resolve to check the source directory for the unbuilt package in question, trigger the build with the originating rez-build arguments, and re-attempt the resolve, continuing as needed.

Start by reviewing the existing dependency-resolving logic and the rez-build command mentioned in the issue. Determine how build order and missing-package resolution currently work; done would mean a defined, tested mechanism for building required packages in dependency order from a single command.

Written by the indexing model from the issue text.