flake: rework the nixpkgs init code

flake.nix

@@ -22,6 +22,10 @@
         (import "${lix-module}/overlay.nix" { inherit lix; })
       ];
       forAllSystems = nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed;
+      libVersionInfoOverlay = import "${nixpkgs}/lib/flake-version-info.nix" nixpkgs;
+      # this is taken from upstream. if upstream changes, the code here needs to be updated to match
+      addLibVersionInfo = lib: lib.extend libVersionInfoOverlay;
+      lib-base = addLibVersionInfo (import "${nixpkgs}/lib");
     in {
       # we don't just use nix.registry.whatever.flake = self
       # the reason for this is to be able to handle a flake.lock containing an entry for this
@@ -42,8 +46,41 @@
       # the nix path entry for self
       meta.path-entry = "dragnpkgs-unstable=flake:dragnpkgs-unstable";
 
-      lib = nixpkgs.lib.extend (final: prev: {
-        licenses = prev.licenses // { fyptl = import ./lib/licenses/fyptl.nix; };
+      lib = (lib-base.extend (import ./lib/overlay.nix)).extend (final: prev: {
+        # initializes regular upstream nixpkgs with the given arguments
+        nixpkgs-custom = { system, ... } @ args: (
+          (import "${nixpkgs}" args).extend (final: prev: {
+            lib = addLibVersionInfo prev.lib;
+          })
+        );
+
+        # initializes dragnpkgs with its overlays and default config using the given arguments
+        dragnpkgs-custom = { system, ... } @ args: let
+          unsafeConf = if builtins.hasAttr "extraBuiltins" builtins then (
+            let conf = builtins.extraBuiltins; in
+            if builtins.isAttrs conf then conf else {}
+          ) else {};
+          possiblyCommitCrimes =
+          if
+            builtins.hasAttr "dragnpkgs" unsafeConf &&
+            builtins.isAttrs unsafeConf.dragnpkgs &&
+            builtins.hasAttr "possiblyCommitCrimes" unsafeConf.dragnpkgs &&
+            builtins.isBool unsafeConf.dragnpkgs.possiblyCommitCrimes
+          then
+            unsafeConf.dragnpkgs.possiblyCommitCrimes
+          else
+            false;
+        in
+          final.nixpkgs-custom (args // {
+            overlays = overlays ++ (args.overlays or []);
+            config = (args.config or {}) // {
+              allowlistedLicenses = (final.optionals
+                possiblyCommitCrimes
+                [ final.licenses.fyptl ]) ++ (args.config.allowlistedLicenses or []);
+            };
+          });
+
+        nixos = import "${nixpkgs}/nixos/lib" { lib = final; };
 
         nixosSystem = args:
           import "${nixpkgs}/nixos/lib/eval-config.nix" (
@@ -192,36 +229,9 @@
       });
 
       legacyPackages = forAllSystems (system:
-        let
-          unsafeConf = if builtins.hasAttr "extraBuiltins" builtins then (
-            let conf = builtins.extraBuiltins; in
-            if builtins.isAttrs conf then conf else {}
-          ) else {};
-          possiblyCommitCrimes =
-          if
-            builtins.hasAttr "dragnpkgs" unsafeConf &&
-            builtins.isAttrs unsafeConf.dragnpkgs &&
-            builtins.hasAttr "possiblyCommitCrimes" unsafeConf.dragnpkgs &&
-            builtins.isBool unsafeConf.dragnpkgs.possiblyCommitCrimes
-          then
-            unsafeConf.dragnpkgs.possiblyCommitCrimes
-          else
-            false;
-        in
-        nixpkgs.legacyPackages.${system}.appendOverlays (overlays ++
-          [(final: prev: {
-            stdenv = prev.stdenv.override {
-              config = prev.config // {
-                allowlistedLicenses = final.lib.optionals
-                  possiblyCommitCrimes
-                  [ final.lib.licenses.fyptl ];
-              };
-            };
-          })])
+        self.lib.dragnpkgs-custom { inherit system; }
       );
 
-      nixosModules = nixpkgs.nixosModules;
-
       templates = {
         default = {
           path = ./templates/default;

lib/overlay.nix

@@ -0,0 +1,3 @@
+final: prev: {
+  licenses = prev.licenses // { fyptl = import ./licenses/fyptl.nix; };
+}

overlay.nix

@@ -1,7 +1,5 @@
 final: prev: {
-  lib = prev.lib.extend (lfinal: lprev: {
-    licenses = lprev.licenses // { fyptl = import ./lib/licenses/fyptl.nix; };
-  });
+  lib = prev.lib.extend (import ./lib/overlay.nix);
 
   fetchFromSteam = prev.callPackage ./lib/fetchsteam {};
   fetchb4 = prev.callPackage ./lib/fetchb4 {};