[Nix-dev] Overriding by removing a derivation attribute

[Kosyrev Serge]

I want to override a Haskell derivation, but in the particular case
it is not enough to change the 'src' attribute -- I also need to stop the
derivation supplying an alternate .cabal file:

      aeson = haskell.lib.overrideCabal old.aeson (oldAttrs: {
        editedCabalFile = null; # <----
        src = pkgs.fetchgit {
                url    = https://github.com/bos/aeson;
                rev    = "d9f1ad357e5dc28c381099814e7cce0e68cf2b6a";
                sha256 = "0nzajw4ia2s7kjjygw9xddrfa1aq2kq960bm9wgj8b34manmyh0f";
        };
      });

Naturally, this doesn't work as desired (the file still gets supplied),
and so the question is -- how is one supposed to achieve that?

-- 
с уважениeм / respectfully,
Косырев Сергей