Compiling cabal with GHC HEAD

[Oleg Grenrus]

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 <ezyang at mit.edu> 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/525e0680505c74f42a321e55b357a27222790628
>> 
>> 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?
> 

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