build: add initial nix build system

flake.nix

@@ -0,0 +1,27 @@
+{
+  inputs = {
+    uninix.url = "github:pauliesnug/uninix";
+    flake-utils.follows = "uninix/flake-utils";
+    nixpkgs.follows = "uninix/nixpkgs";
+  };
+
+  outputs = inputs: with inputs;
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs {
+          inherit system;
+          overlays = [ uninix.overlays.gradle ];
+        };
+
+        pkgSystem = pkgs.builder.gradle.makePackageSet {
+          packageFn = import ./uni.demo.nix;
+          targets = "auto";
+        };
+      in rec {
+        packages = {
+          oneconfig = (pkgSystem.workspace.minecraft.eachDefaultVersion {}).bin;
+          default = packages.oneconfig;
+        };
+      }
+    );
+}

uni.demo.nix

@@ -0,0 +1,37 @@
+# This DEMO file was @generated by uninix alpha-1
+# IT is not intended to be used in production or manually edited.
+# This is a basic demo file intended to be a placeholder until
+# the official uni.adapt.nix file is able to be configured.
+
+args@{
+  release ? true,
+  uninixLib,
+  target ? null,
+  lib,
+  workspaceSource,
+  gradle,
+  compileMode ? null,
+  gradlePackages,
+  workspaceGen,
+}:
+let
+  workspaceSource = if args.workspaceSource == null then ./. else args.workspaceSource;
+in let
+  inherit (uninixLib) genDrvsByVersion decideVersion;
+  inherit (gradle) makeGradlePkg fetchGradle;
+  versionsBySettings = {};
+  overridableMakeGradlePkg = f:
+    let
+      drvs = genDrvsByVersion versionsBySettings ({ version, versionName }: makeGradlePkg ({ inherit release version target; } // (f versionName)));
+    in { compileMode ? null, versionName ? decideVersion compileMode release }:
+      let drv = drvs.${versionName}; in if compileMode == null then drv else drv.override { inherit compileMode; };
+in
+{
+  uninixVersion = "alpha-1";
+  workspace = workspaceGen;
+  "unknown".workspace.version = overridableMakeGradlePkg (versionName: {
+    name = workspaceGen.minecraft.sort.name;
+    version = workspaceGen.minecraft.sort.version;
+    src = fetchGradle workspaceSource;
+  });
+}