Yes, this is a common hazard when trying to use cabal-install with GHC HEAD. My recommendation is to use the Cabal tip distributed with GHC HEAD. Edward Excerpts from Oleg Grenrus's message of 2015-08-26 12:29:16 -0700:

Ah, so this happens because GHC HEAD has Cabal-1.23.0.0 bundled with it. I see. And as Cabal master is also 1.23.0.0 they don’t really work together (i.e. cabal-install uses system Cabal).

Ok, maybe we can wait till GHC’s Cabal reference-commit will be bumped, if not already.

Thanks for the explanation.

- Oleg

...

On 19 Aug 2015, at 19:19, Edward Z. Yang wrote:

Oh, this is irritating.

The problem is we recently updated Cabal the library to get rid of InstalledPackageInfo_ (so there is only InstalledPackageInfo now) but it looks like in some situations cabal-install can be compiled with an old version of Cabal (as is happening to you). I suppose an appropriate remedy is to bump the Cabal library dependency in cabal-install so we don't attempt to use the old Cabal; alternately we could preprocessor macro to make it work in both cases.

Edward

Excerpts from Oleg Grenrus's message of 2015-08-19 07:46:56 -0700:

...

I tried to fix compilation of Cabal using Cabal HEAD. It’s trivial patch:

https://github.com/phadej/cabal/commit/525e0680505c74f42a321e55b357a27222790...

but it breaks build on every other released GHC:

https://travis-ci.org/phadej/cabal/builds/76288656

—

The original issue GHC-7.11 complained was:

Distribution/Client/Types.hs:71:10: error: Illegal instance declaration for ‘PackageFixedDeps InstalledPackageInfo’ (All instance types must be of the form (T t1 ... tn) where T is not a synonym. Use TypeSynonymInstances if you want to disable this.) In the instance declaration for ‘PackageFixedDeps InstalledPackageInfo’

So I had to add TypeSynonymInstances and FlexibleInstances

And also had to change import of InstalledPackageInfo(exposed) in Haddock module.

—

At this point I’m really confused. I cannot find ‘InstalledPackageInfo_’ symbol anywhere. Can someone explain what happens?