nixpkgs-bootstrap.mkNixpkgs: remove the overrideAttrs call, and inline its functionality into applyPatches

pkgs/by-name/nixpkgs-bootstrap/mkNixpkgs.nix

@@ -101,9 +101,15 @@ let
     fetchpatch2' = if fetchpatch2 != null then fetchpatch2 else unpatchedNixpkgs.fetchpatch2;
 
     patchedSrc = applyPatches' {
-      src = src';
       name = "nixpkgs-patched-uninsane";
       inherit version;
+
+      src = {
+        # required by unstableGitUpdater
+        gitRepoUrl = "https://github.com/NixOS/nixpkgs.git";
+        inherit rev;
+      } // src';
+
       patches = import ./patches.nix { fetchpatch2 = fetchpatch2'; };
       # skip applied patches
       prePatch = ''
@@ -112,34 +118,10 @@ let
            OUT=$($realpatch "$@") || echo "$OUT" | grep "Skipping patch" -q
         }
       '';
-    };
 
-    nixpkgsArgs = commonNixpkgsArgs // {
-      config = {
-        allowUnfree = true;  # NIXPKGS_ALLOW_UNFREE=1
-        allowBroken = true;  # NIXPKGS_ALLOW_BROKEN=1
-      };
-    } // (if (system != localSystem) then {
-      # XXX(2023/12/11): cache.nixos.org uses `system = ...` instead of `hostPlatform.system`, and that choice impacts the closure of every package.
-      # so avoid specifying hostPlatform.system on non-cross builds, so i can use upstream caches.
-      crossSystem = system;
-    } else {});
-    nixpkgs = import patchedSrc nixpkgsArgs;
-  in
-    patchedSrc.overrideAttrs (base: {
-      # attributes needed for update scripts.
-      # TODO: should be possible to pass these straight through `applyPatches` instead of using `overrideAttrs`.
-      inherit version;
-      pname = "nixpkgs";
-      passthru = (base.passthru or {}) // {
+      passthru = {
         pkgs = nixpkgs;
 
-        src = {
-          # required by unstableGitUpdater
-          gitRepoUrl = "https://github.com/NixOS/nixpkgs.git";
-          inherit rev;
-        } // src';
-
         # required so that unstableGitUpdater can know in which file the `rev` variable can be updated in.
         meta.position = let
           position = builtins.unsafeGetAttrPos "rev" args;
@@ -157,7 +139,21 @@ let
           inherit branch;
         };
       };
-    })
+    };
+
+    nixpkgsArgs = commonNixpkgsArgs // {
+      config = {
+        allowUnfree = true;  # NIXPKGS_ALLOW_UNFREE=1
+        allowBroken = true;  # NIXPKGS_ALLOW_BROKEN=1
+      };
+    } // (if (system != localSystem) then {
+      # XXX(2023/12/11): cache.nixos.org uses `system = ...` instead of `hostPlatform.system`, and that choice impacts the closure of every package.
+      # so avoid specifying hostPlatform.system on non-cross builds, so i can use upstream caches.
+      crossSystem = system;
+    } else {});
+    nixpkgs = import patchedSrc nixpkgsArgs;
+  in
+    patchedSrc
   ;
 in
   mkNixpkgs