Old haskell.nix code gives `value is a function while a set was expected`

[hamishmack]

Once we remove the backwards compatibility support we may see some
value is a function while a set was expected errors with old
haskell.nix code that looks like this:

import <nixpkgs> { inherit (import haskellNixSrc) config overlays system; }

solution is to change it to something like:

import <nixpkgs> { inherit ((import haskellNixSrc {}).nixpkgsArgs) config overlays system; }

or just:

import <nixpkgs> (import haskellNixSrc {}).nixpkgsArgs

[hamishmack]

It turns out the deprecation warning was not being printed so we have switched V1 interface back on for now (and fixed the warning). We will probably switch it off again once we are confident everyone has upgraded so I will leave this open for then.

[michaelpj]

I think we are well past this now.