In reply to @jean-paul.:matrix.org
nope, Linux - but CircleCI

Just guessing, but is it because the kernel has IPv6 disabled via sysctl or perhaps even via kconfig?

Nix builds are sensitive to the host kernel.

In reply to @bglgwyng:matrix.org
Can we override argument passed to cabal2nix result with haskellPackages.override?
For example, if I want to replace native zlib used by haskell package zlib, I can use overrideCabal to modify librarySystemDepends.
However, is it possible to just override the value passed to cabal2nix, which is a lambda with arguments { mkDervation, base, ..., zlib}?

{
  "zlib" = callPackage
    ({ mkDerivation, base, bytestring, QuickCheck, tasty
     , tasty-quickcheck, zlib
     }:
     mkDerivation {
       pname = "zlib";
       version = "0.6.3.0";
       sha256 = "1nh4xsm3kgsg76jmkcphvy7hhslg9hx1s75mpsskhi2ksjd9ialy";
       revision = "5";
       editedCabalFile = "0mj3f7ql54p0pfa5a6q4xv4ci8xf00616ls0nyadpmlqbb4qilwn";
       libraryHaskellDepends = [ base bytestring ];
       librarySystemDepends = [ zlib ];
       testHaskellDepends = [
         base bytestring QuickCheck tasty tasty-quickcheck
       ];
       description = "Compression and decompression in the gzip and zlib formats";
       license = lib.licenses.bsd3;
     }) {inherit (pkgs) zlib;};
}

this is from hackage-pacakges.nix, and I'm not sure if I have any chance to override zlib when callPackage is already called.

So you want to be able to e.g. add extra arguments to the cabal2nix command?

IIRC that's possible with callCabal2nix and obviously if you implement the command yourself. Overriding is trickier but should still be possible through overriding callCabal2nix (this isn't pretty).

I'm having trouble understanding why overriding the result is insufficient in your case.

splitmix's definition is like

"splitmix" = callPackage
    ({ mkDerivation, async, base, ..., testu-01 }:
     mkDerivation {