ANNOUNCE: GHC 6.12.1 Release Candidate 1

[Simon Marlow]

On 14/10/2009 04:43, Antoine Latter wrote:
> On Sun, Oct 11, 2009 at 3:41 PM, Ian Lynagh<igloo at earth.li>  wrote:
>>
>> Hi all,
>>
>> We are pleased to (finally!) announce the first release candidate
>> for GHC 6.12.1:
>>
>>     http://darcs.haskell.org/~ghc/dist/6.12.1rc1/
>>
>> As well as the source tarball:
>>     ghc-6.12.0.20091010-src.tar.bz2
>> there are installers for Windows (i386) and OS X (i386), and binary
>> distributions for x86_64/Linux and i386/Linux. For the Linux binary
>> distributions, the "linux-n" tarballs are recommended over the "linux"
>> tarballs.
>>
>>
>> Please test as much as possible; bugs are much cheaper if we find them
>> before the release!
>>
>>
>
> Here is my tale of woe. I'm running this on Mac OS X 10.6.
>
> I tried to install the syb-with-class package off of hackage, which
> initially failed because of the changes to the template-haskell
> package installed with 6.12.1rc1.
>
> So I think to myself "Oh! I'll just put an upper bound on the version
> of template-haskell used in the .cabal file for syb, and install the
> old version off of hackage".
>
> The current version of template-haskell installs fine on 6.12.1rc1
> with a couple minor tweaks (to compensate for StringConstr not being
> present in Data.Data anymore).
>
> But then when I try to build syb-with-class against the old
> template-haskell lib I get the following error:
>
>>>>>>
> $ ./Setup build
> Preprocessing library syb-with-class-0.5.1...
> Building syb-with-class-0.5.1...
> [3 of 4] Compiling Data.Generics.SYB.WithClass.Derive (
> Data/Generics/SYB/WithClass/Derive.hs,
> dist/build/Data/Generics/SYB/WithClass/Derive.o )
>
> Data/Generics/SYB/WithClass/Derive.hs:23:0:
>      Bad interface file:
> /Users/alatter/.cabal/lib/template-haskell-2.3.0.1/ghc-6.12.0.20091010/Language/Haskell/TH.hi
>          Something is amiss; requested module
> template-haskell-2.3.0.1:Language.Haskell.TH differs from name found
> in the interface file template-haskell:Language.Haskell.TH
> <<<<<
>
> Has anyone seen this before? Are there any tools I can use to peer
> into .hi files to get more information about what could be wrong?

template-haskell is a one of the packages that we call "wired-in", 
because GHC needs to generate references to some of the things that it 
defines.  To make GHC independent of the version of the template-haskell 
package, we internally strip off the version number when referring to 
template-haskell.

Now, this doesn't completely explain the error you're seeing.  When it 
starts up, GHC has to decide which template-haskell package is the 
"wired-in" one, and my guess is that it picked the other one (because it 
is newer).  You could find out by running GHC with the -v flag.  I think 
GHC is assuming that when you have multiple versions of a wired-in 
package that the older ones are wrappers around the newer ones (like 
base-3 and base-4), but that assumption doesn't hold in your case.

Installing a new version of a wired-in package is going to be 
problematic, but we ought to be able to at least improve the diagnostics.

Cheers,
	Simon