PackageIndex will be removed from Cabal 1.26

[ezyang]

Via this PR haskell/cabal#3525

Out of all the packages in Hackage, hackage-server is the only one using the PackageIndex in a nontrivial way. Will you be able to refactor to use the new Distribution.Compat.Graph interface or should I put in a backwards compatibility shim for you?

[gbaz]

Are you sure it uses Distribution.Simple.PackageIndex? It looks to me that it defines its own Distribution.Server.PackageIndex, but I may be missing something?

[ezyang]

Nope, I just saw PackageIndex. If it defines its own, false alarm!