feat: add nix flake (#631)

.envrc

@@ -0,0 +1,10 @@
+if ! has nix_direnv_version || ! nix_direnv_version 3.0.5; then
+  source_url "https://raw.githubusercontent.com/nix-community/nix-direnv/3.0.5/direnvrc" "sha256-zelF0vLbEl5uaqrfIzbgNzJWGmLzCmYAkInj/LNxvKs="
+fi
+
+watch_file flake.nix
+watch_file flake.lock
+if ! use flake . --impure
+then
+  echo "Flake could not be used... something is broken :(" >&2
+fi

.gitignore

@@ -1,3 +1,4 @@
 .gradle
 build
 .idea
+.direnv

flake.nix

@@ -0,0 +1,29 @@
+{
+  description = "Minimal example of building Kotlin with Gradle and Nix";
+
+  inputs = {nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";};
+
+  inputs.systems.url = "github:nix-systems/default";
+
+  inputs.flake-utils.url = "github:numtide/flake-utils";
+  inputs.flake-utils.inputs.systems.follows = "systems";
+
+  outputs = {
+    nixpkgs,
+    flake-utils,
+    ...
+  }:
+    flake-utils.lib.eachDefaultSystem (system: let
+      pkgs = import nixpkgs {inherit system;};
+      updateLocks = pkgs.callPackage ./update-locks.nix {};
+    in {
+      devShells.default = pkgs.mkShell {
+        buildInputs = with pkgs; [
+          gradle_8
+          temurin-bin-21
+          updateLocks
+          ktlint
+        ];
+      };
+    });
+}

update-locks.nix

@@ -0,0 +1,17 @@
+{
+  writeShellScriptBin,
+  gradle,
+  yq,
+}:
+writeShellScriptBin "update-locks" ''
+  set -eu -o pipefail
+  ${gradle}/bin/gradle dependencies --write-locks
+  ${gradle}/bin/gradle --write-verification-metadata sha256 dependencies
+  ${yq}/bin/xq '
+      ."verification-metadata".components.component |
+      map({ group: ."@group", name: ."@name", version: ."@version",
+        artifacts: [([.artifact] | flatten | .[] | {(."@name"): .sha256."@value"})] | add
+      })
+    ' gradle/verification-metadata.xml > deps.json
+  rm gradle/verification-metadata.xml
+''