cataclysmDDA: add utility function `attachPkgs`

pkgs/games/cataclysm-dda/default.nix

···
     buildMod
     buildSoundPack
     buildTileSet
-    wrapCDDA;
+    wrapCDDA
+    attachPkgs;
 
     inherit pkgs;
   };

pkgs/games/cataclysm-dda/git.nix

···
-{ lib, callPackage, CoreFoundation, fetchFromGitHub, pkgs, wrapCDDA
+{ lib, callPackage, CoreFoundation, fetchFromGitHub, pkgs, wrapCDDA, attachPkgs
 , tiles ? true, Cocoa
 , debug ? false
 , useXdgDir ? false
···
       "VERSION=git-${version}-${lib.substring 0 8 src.rev}"
     ];
 
-    passthru = common.passthru // {
-      pkgs = pkgs.override { build = self; };
-      withMods = wrapCDDA self;
-    };
-
     meta = common.meta // {
       maintainers = with lib.maintainers;
       common.meta.maintainers ++ [ rardiol ];
···
   });
 in
 
-self
+attachPkgs pkgs self

pkgs/games/cataclysm-dda/lib.nix

···
 { callPackage }:
 
-{
+rec {
   buildMod = callPackage ./builder.nix {
     type = "mod";
   };
···
   };
 
   wrapCDDA = callPackage ./wrapper.nix {};
+
+  # Required to fix `pkgs` and `withMods` attrs after applying `overrideAttrs`.
+  #
+  # Example:
+  #     let
+  #       myBuild = cataclysmDDA.jenkins.latest.tiles.overrideAttrs (_: {
+  #         x = "hello";
+  #       });
+  #
+  #       # This refers to the derivation before overriding! So, `badExample.x` is not accessible.
+  #       badExample = myBuild.withMods (_: []);
+  #
+  #       # `myBuild` is correctly referred by `withMods` and `goodExample.x` is accessible.
+  #       goodExample = let
+  #         inherit (cataclysmDDA) attachPkgs pkgs;
+  #       in
+  #       (attachPkgs pkgs myBuild).withMods (_: []);
+  #     in
+  #     goodExample.x  # returns "hello"
+  attachPkgs = pkgs: super:
+  let
+    self = super.overrideAttrs (old: {
+      passthru = old.passthru // {
+        pkgs = pkgs.override { build = self; };
+        withMods = wrapCDDA self;
+      };
+    });
+  in
+  self;
 }

pkgs/games/cataclysm-dda/stable.nix

···
-{ lib, callPackage, CoreFoundation, fetchFromGitHub, pkgs, wrapCDDA
+{ lib, callPackage, CoreFoundation, fetchFromGitHub, pkgs, wrapCDDA, attachPkgs
 , tiles ? true, Cocoa
 , debug ? false
 , useXdgDir ? false
···
       sha256 = "15l6w6lxays7qmsv0ci2ry53asb9an9dh7l7fc13256k085qcg68";
     };
 
-    passthru = common.passthru // {
-      pkgs = pkgs.override { build = self; };
-      withMods = wrapCDDA self;
-    };
-
     meta = common.meta // {
       maintainers = with lib.maintainers;
       common.meta.maintainers ++ [ skeidel ];
···
   });
 in
 
-self
+attachPkgs pkgs self