pkgs.haskell.lib.overrideCabal

The function overrideCabal lets you alter the arguments to the mkDerivation function.

Example:

First, note how the aeson package is constructed in hackage-packages.nix:

"aeson" = callPackage ({ mkDerivation, attoparsec, <snip>
                       }:
                         mkDerivation {
                           pname = "aeson";
                           <snip>
                           homepage = "https://github.com/bos/aeson";
                         })

The mkDerivation function of haskellPackages will take care of putting the homepage in the right place, in meta.

> haskellPackages.aeson.meta.homepage
"https://github.com/bos/aeson"

> x = haskell.lib.overrideCabal haskellPackages.aeson (old: { homepage = old.homepage + "#readme"; })
> x.meta.homepage
"https://github.com/bos/aeson#readme"

Noogle detected

overrideCabal = drv: f: compose.overrideCabal f drv;