Following up from discussion here: https://groups.google.com/a/chromium.org/forum/#!topic/gn-dev/43HKY99h8Mw

The feature request is the following work flow:

1. A #includes "b" in B.
2. B is not visible to A.
3. As we do today, if there' a path (with missing "public"), print it -- this is very helpful :)
4. Also answer the query: "What is the shortest public path from B to a target that is visible to A?" This should not be an expensive operation. Remember, B's visibility is limited! I would expect this path to be of length 1 or 2 in most cases. (A hidden source set is contained by an exposing component).
5. It might also be useful to print a comment above the "visibility" annotation in the gn file.