As discussed in #1274, we should unregister add-source dependencies before reinstalling to avoid the warning about dangerous reinstalls.
I'm starting to think that the warning is not such a bad thing after all, since it's good to know what is going on under the hood. Unregistering add-source deps won't avoid the warnings when we're reinstalling the dependencies of add-source dependencies and may probably change the behaviour of the solver.
Removing the 1.18 milestone since I'm not sure that this is fixable without making the solver do the wrong thing.
Looks like this should just be closed?