Building haddock documentaion for hackage fails.

[mmzx]

The sequence of commands explained in here fails with the result

CallStack (from HasCallStack):
  error, called at ./Distribution/Client/CmdErrorMessages.hs:329:14 in main:Distribution.Client.CmdErrorMessages

It would be nice to have the code documentation uploaded onto hackage as well.

[kukimik]

This looks related: haskell/cabal#6679.