module ‘free-4.6.1:Main’ is defined in multiple files

[Mateusz Kowalczyk]

Greetings,

First of all to people reading this at ghc-devs, I don't expect this to
be a direct problem caused by GHC but who knows, so I'm CC'ing it anyway.

As you might know, GHC 7.8.1 is scheduled to release Very Soon™  (later
today?). We got a report at Haddock Trac few weeks ago about a strange
error, see http://trac.haskell.org/haddock/ticket/284.

I have asked about this on cabal-devel before and Mikhail said that
maybe it's https://github.com/haskell/cabal/pull/1374 but it's unlikely
because the changes aren't ran by default.

Today I got new reports of this problem and so far everyone on OSX seems
to be affected! This suddenly became a big problem. To replicate:

1. Find OSX machine
2. Get GHC 7.8 rc2 package (which includes Haddock at that stage)
3. git clone git at github.com:ekmett/free.git && cd free
4. cabal install --only-dependencies --enable-documentation && cabal
configure && cabal haddock

The reason I'm barking up cabal-devel and ghc-devs is because I honestly
can not think of anything that has changed since Haddock 2.13.2.1 that
could possibly cause this.

Does anyone have any idea at all? I think it would be very bad to
release now and have everyone on OSX unable to build docs.

FYI I get build docs on 32-bit Linux. No idea about Windows.

Thanks, I hope to hear back soon.

PS: How does one go about downgrading Cabal and cabal-install? If we
wanted to check whether cabal is the problem, how?

-- 
Mateusz K.