Display package at the origin of a failed dependency

[erothe]

When building several hundred of packages in one go, a technique that point quickly to the package that is at the origin of a failing dependency is valuable. This can be tricky because the number of higher degree dependencies can be high. Suppose that in your spec, you requested the installation of package A. But package A depends on package B which in turn depends on package C, etc. Consider the following scenario:

A > B > C > D > E

How to get to A given that E failed, your spec list, and the list of packages successfully installed ?