haskell-modules: implement overrideScope method for deep overriding

deepOverride turns out to be completely unfeasible for non-trivial overrides.
Nix evaluates for an eternity, and then comes back saying:

  Too many heap sections: Increase MAXHINCR or MAX_HEAP_SECTS
  nix-instantiate killed by signal 6

The hand-written deep-override, on the other hand, performs the job in a
fraction of a second, no problem.

All bow to Russell O'Connor!

1 files changed, 5 insertions, 1 deletions

diff --git a/pkgs/development/haskell-modules/default.nix b/pkgs/development/haskell-modules/default.nix
index 846f85da66ff..d65ebd63c751 100644
--- a/pkgs/development/haskell-modules/default.nix
+++ b/pkgs/development/haskell-modules/default.nix
@@ -31,8 +31,12 @@ let
         mkDerivation = drv: args.mkDerivation (drv // f drv);
       });
 
+      callPackageWithScope = scope: drv: args: (stdenv.lib.callPackageWith scope drv args) // {
+        overrideScope = f: callPackageWithScope (fix (extend scope.__unfix__ f)) drv args;
+      };
+
       defaultScope = pkgs // pkgs.xlibs // pkgs.gnome // self;
-      callPackage = drv: args: stdenv.lib.callPackageWith defaultScope drv args;
+      callPackage = drv: args: callPackageWithScope defaultScope drv args;
 
     in
       import ./hackage-packages.nix { inherit pkgs stdenv callPackage; } self // {