[Nix-dev] Use GHC 7.10.1 as default Haskell compiler in nixpkgs

[Mateusz Kowalczyk]

On 04/03/2015 04:31 PM, Mateusz Kowalczyk wrote:
> On 04/02/2015 11:21 PM, Peter Simons wrote:
>> Hi guys,
>>
>> I believe that we should switch our default compiler to GHC 7.10.1
>> within the next three or four weeks -- assuming that no major bug is
>> discovered in that compiler. It is true that this update will break some
>> packages, but GHC versions prior to 7.10.x are a disaster for
>> distributions like us because they generate non-deterministic library
>> IDs. This means that two builds running in identical environments can
>> produce outputs that differ and that break binary compatibility when
>> linked by other libraries. This is a nightmare for systems like Hydra,
>> and I've just had to rebuild all our Haskell packages [1] for the
>> umpteenth time because of that bug. GHC 7.10.1 is supposed to fix that
>> issue, so I'd say let's go for it.
> 
> If not fix, it should be much better at least. If someone hits the
> problem with 7.10, let me know.
> 
>> Those of you who don't want to update can stick to GHC 7.8.4, of course,
>> it's just that Hydra will no longer provide binaries for that version
>> after the switch.
>>
>> Also, I'd like to remove all code related to the old Haskell package set
>> from Nixpkgs shortly after the switch, to make sure that obsolete code
>> won't make it into the next release branch. If you haven't migrated to
>> Haskell NG yet ... now would be a good time to do it. (I'm looking at
>> you, Agda.)
> 
> I can update the Agda stuff today.
> 
>> How do you guys feels about that approach? Any concerns? Other
>> suggestions?
>>
>> Best regards,
>> Peter
>>
>>
>> [1] https://github.com/NixOS/nixpkgs/commit/945269a48fa8b91024e18a72b485797eeca308ee
>>
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> 
> 

…or, well, I would have but the Hackage-available Agda version has the
cpphs version issue but from what I can tell, here are the steps to
migrate Agda over to haskell-ng:

in all-packages.nix change inherits and references to haskellngPackages
(AgdaStdlib package). For the ‘agda’ builder, just change the Agda arg
to use haskellngPackages.Agda.

Then for cleanup, move out the expression for AgdaStdlib to libraries/agda.

-- 
Mateusz K.