Restore broken Nix build (#311)

default.nix

@@ -24,20 +24,11 @@
       };
       utoipa-swagger-ui = attrs: rec {
         # utoipa-swagger-ui tries to redownload swagger-ui, which is blocked by Nix's sandboxing
-        # so we download it instead, and put it where it expects to be cached
-        preConfigure =
-          let
-            swaggerUi = pkgs.fetchurl {
-              url = "https://github.com/swagger-api/swagger-ui/archive/refs/tags/v5.17.3.zip";
-              hash = "sha256-zrb8feuuDzt/g6y7Tucfh+Y2BWZov0soyNPR5LBqKx4=";
-            };
-          in ''
-            mkdir -p target/build/utoipa-swagger-ui.out
-            ln -s "${swaggerUi}" target/build/utoipa-swagger-ui.out/swagger-ui.zip
-          '';
-        # Build script only supports fetching from HTTP, not file URLs
-        # Last path element decides the cache key, which we rely on above
-        SWAGGER_UI_DOWNLOAD_URL = "file:///invalid-path/swagger-ui.zip";
+        # so we download it instead, and tell it to use that
+        SWAGGER_UI_DOWNLOAD_URL = "file://${pkgs.fetchurl {
+          url = "https://github.com/swagger-api/swagger-ui/archive/refs/tags/v5.17.3.zip";
+          hash = "sha256-zrb8feuuDzt/g6y7Tucfh+Y2BWZov0soyNPR5LBqKx4=";
+        }}";
       };
     };
   }