taffybar: restore ability to override ghcWithPackages arg

pkgs/applications/window-managers/taffybar/default.nix

@@ -1,7 +1,7 @@
-{ lib, stdenv, haskellPackages, makeWrapper, packages ? (x: []) }:
+{ lib, stdenv, ghcWithPackages, taffybar, makeWrapper, packages ? (x: []) }:
 
 let
-  taffybarEnv = haskellPackages.ghc.withPackages (self: [
+  taffybarEnv = ghcWithPackages (self: [
     self.taffybar
   ] ++ packages self);
 in stdenv.mkDerivation {
@@ -15,5 +15,14 @@ in stdenv.mkDerivation {
       --set NIX_GHC "${taffybarEnv}/bin/ghc"
   '';
 
-  inherit (haskellPackages.taffybar) meta;
+  # Trivial derivation
+  preferLocalBuild = true;
+  allowSubstitutes = false;
+
+  # For hacking purposes
+  passthru.env = taffybarEnv;
+  buildInputs = [ taffybarEnv ];
+  shellHook = "eval $(egrep ^export ${taffybarEnv}/bin/ghc)";
+
+  inherit (taffybar) meta;
 }

pkgs/top-level/all-packages.nix

@@ -26320,7 +26320,9 @@ in
     # customConfig = builtins.readFile ./tabbed.config.h;
   };
 
-  taffybar = callPackage ../applications/window-managers/taffybar {};
+  taffybar = callPackage ../applications/window-managers/taffybar {
+    inherit (haskellPackages) ghcWithPackages taffybar;
+  };
 
   tagainijisho = callPackage ../applications/office/tagainijisho {};