[Haskell-cafe] Build regressions due to GHC 7.6

[Bryan O'Sullivan]

Since the release of the GHC 7.6 RC, I've been going through my packages
and fixing up build problems so that people who upgrade to 7.6 will have a
smooth ride.

Sad to say, my experience of 7.6 is that it has felt like a particularly
rough release for backwards incompatibility. I wanted to quantify the pain,
so I did some research, and here's what I found.

I maintain 25 open source Haskell packages. Of these, the majority have
needed updates due to the GHC 7.6 release:

   - base16-bytestring
   - blaze-textual
   - bloomfilter
   - configurator
   - criterion
   - double-conversion
   - filemanip
   - HDBC-mysql
   - mwc-random
   - pcap
   - pool
   - riak-haskell-client
   - snappy
   - text
   - text-format
   - text-icu

That's 16 out of 25 packages I've had to update. I've also either reported
bugs on, or had to fix, several other people's packages along the way
(maybe four?). So let's say I've run into problems with 20 out of the
combined 29 packages of mine and my upstreams.

The reasons for these problems fall into three bins:

   - Prelude no longer exports catch, so a lot of "import Prelude hiding
   (catch)" had to change.
   - The FFI now requires constructors to be visible, so "CInt" has to be
   imported as "CInt(..)".
   - bytestring finally got bumped to 0.10, so many upper bounds had to be
   relaxed (*cf* my suggestion that the upper-bounds-by-default policy is
   destructive).

It has been a lot of work to test 29 packages, and then modify, rebuild,
and release 20 of them. It has consumed most of my limited free time for
almost two weeks. Worse, this has felt like make-work, of no practical
benefit to anyone beyond scrambling to restore the status quo ante.

If over half of my packages needed fixing, I'm alarmed at the thought of
the effects on the rest of Hackage.

I'm torn over this. I understand and agree with the impetus to improve the
platform by tidying things up, and yet just two seemingly innocuous changes
(catch and FFI) have forced me to do a bunch of running to stand still.

I don't have any suggestions about what to do; I know that it's hard to
estimate the downstream effects of what look like small changes. And so I'm
not exactly complaining. Call this an unhappy data point.
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