Add an overlay to the flake.

flake.nix

@@ -57,43 +57,10 @@
           pkgs = import nixpkgs {
             inherit system overlays;
           };
-          build_wasm =
+          appliedOverlay = self.overlays.default pkgs pkgs;
-            {
-              bindgenTarget ? null,
-            }:
-            (pkgs.callPackage ./nix/package.nix {
-              targetBins = [
-                "wasm"
-              ];
-              features = [ "wasm" ];
-              cargoBuildTarget = "wasm32-unknown-unknown";
-              buildType = "wasm";
-            }).overrideAttrs
-              (
-                old:
-                let
-                  bindgen_command = [
-                    "${pkgs.wasm-bindgen-cli}/bin/wasm-bindgen"
-                    "--target"
-                    bindgenTarget
-                    "--out-dir"
-                    "target/wasm32-unknown-unknown/${bindgenTarget}"
-                    "target/wasm32-unknown-unknown/wasm/wasm.wasm"
-                  ];
-                in
-                {
-                  postBuild = ''
-                    ${pkgs.lib.escapeShellArgs bindgen_command}
-                  '';
-
-                  installPhase = ''
-                    mkdir -p $out/share/${bindgenTarget}
-                    cp target/wasm32-unknown-unknown/${bindgenTarget}/* $out/share/${bindgenTarget}
-                  '';
-                }
-              );
         in
         rec {
+          default = all;
           all = pkgs.symlinkJoin {
             name = "all";
             paths = [
@@ -103,37 +70,86 @@
               wasm_web
             ];
           };
-          library = (pkgs.callPackage ./nix/package.nix { buildLib = true; }).overrideAttrs (
+          inherit (appliedOverlay.organic)
-            old:
+            library
-            let
+            devTools
-            in
+            wasm_bundler
-            {
+            wasm_web
-              installPhase = ''
+            ;
-                mkdir -p $out/lib
-                cp target/*/release/liborganic.rlib $out/lib/
-              '';
-            }
-          );
-          devTools = pkgs.callPackage ./nix/package.nix {
-            targetBins = [
-              "parse"
-              "compare"
-            ];
-            features = [ "compare" ];
-          };
-          wasm_bundler = build_wasm { bindgenTarget = "bundler"; };
-          wasm_web = build_wasm { bindgenTarget = "web"; };
           docker_env = pkgs.buildEnv {
             name = "organic";
             paths = with pkgs; [
-              devTools
+              appliedOverlay.organic.devTools
               bash
               uutils-coreutils-noprefix
               # toybox # Smaller than uutils-coreutils?
             ];
           };
-          default = all;
         }
       );
+      overlays.default = final: prev: {
+        organic = final.lib.makeScope final.newScope (
+          organicScope:
+          let
+            build_wasm =
+              {
+                bindgenTarget ? null,
+              }:
+              (organicScope.callPackage ./nix/package.nix {
+                targetBins = [
+                  "wasm"
+                ];
+                features = [ "wasm" ];
+                cargoBuildTarget = "wasm32-unknown-unknown";
+                buildType = "wasm";
+              }).overrideAttrs
+                (
+                  old:
+                  let
+                    bindgen_command = [
+                      "${final.wasm-bindgen-cli}/bin/wasm-bindgen"
+                      "--target"
+                      bindgenTarget
+                      "--out-dir"
+                      "target/wasm32-unknown-unknown/${bindgenTarget}"
+                      "target/wasm32-unknown-unknown/wasm/wasm.wasm"
+                    ];
+                  in
+                  {
+                    postBuild = ''
+                      ${final.lib.escapeShellArgs bindgen_command}
+                    '';
+
+                    installPhase = ''
+                      mkdir -p $out/share/${bindgenTarget}
+                      cp target/wasm32-unknown-unknown/${bindgenTarget}/* $out/share/${bindgenTarget}
+                    '';
+                  }
+                );
+          in
+          {
+            library = (organicScope.callPackage ./nix/package.nix { buildLib = true; }).overrideAttrs (
+              old:
+              let
+              in
+              {
+                installPhase = ''
+                  mkdir -p $out/lib
+                  cp target/*/release/liborganic.rlib $out/lib/
+                '';
+              }
+            );
+            devTools = organicScope.callPackage ./nix/package.nix {
+              targetBins = [
+                "parse"
+                "compare"
+              ];
+              features = [ "compare" ];
+            };
+            wasm_bundler = build_wasm { bindgenTarget = "bundler"; };
+            wasm_web = build_wasm { bindgenTarget = "web"; };
+          }
+        );
+      };
     };
 }