Linear Ordering of Dependencies with a Topological Sort

A few weeks back I was working on a solution in Visual Studio with about 8 projects or so in it. I attempted to add a reference from Project B to Project A and was greeted with a nice little dialog box letting me know I had accidentally created a circular dependency when adding the new reference. Ooops! But this got me thinking, what algorithm is Visual Studio using to detect circular dependencies? Let's find out...