[Nix-dev] Use of GHC's environment variable GHC_PACKAGE_PATH is incompatible with Cabal. Use the flag --package-db to specify a package database (it can be used multiple times)

[Mateusz Kowalczyk]

On 08/15/2014 05:22 AM, Mateusz Kowalczyk wrote:
> Hi,
> 
> I'd like to know the solution to the error message in the subject. I
> have encountered it in the past if inside a Haskell project I did
> something like
> 
> nix-shell --pure
> eval "$configurePhase" && eval "$buildPhase" && eval "$checkPhase"
> 
> While this bothered me, the workaround was to exit and re-enter the
> shell after buildPhase and run checkPhase then.
> 
> But now I want to actually test a package that this happens in on my
> local Hydra and when it goes to run the test-suite, I get precisely that
> message.
> 
> The package in question is Haddock here which is set to ‘doCheck =
> false’ in nixpkgs even though I personally happen to know that the tests
> do pass when actually ran. Not running the test-suite is obviously not
> acceptable when you're the package maintainer…
> 
> Any ideas?
> 

I find that if I unset GHC_PACKAGE_PATH after ‘eval "$buildPhase"’ then
the tests will run. While one can arrange this with some hooks on
per-package basis, I'd be interested to hear if why we're setting
GHC_PACKAGE_PATH after during the buildPhase to begin with. Perhaps the
default could be that it is not set or if cabal does that, that we unset
it. It seems that if this was useful then we would set it at the point
build starts (before configure or after). AFAIK any packages that make
use of GHC_PACKAGE_PATH just call out to ghc-pkg anyway and put together
a GHC_PACKAGE_PATH from scratch.

Can we just unset/never set GHC_PACKAGE_PATH by default?

-- 
Mateusz K.