build: use flakes for devshell

Author: lineargraph

.envrc

@@ -1,4 +1,4 @@
 #SPDX-FileCopyrightText: 2025 Linnea Gräf <nea@nea.moe>
 #
 #SPDX-License-Identifier: CC0-1.0
-use nix
+use flake

REUSE.toml

@@ -56,3 +56,8 @@ SPDX-FileCopyrightText = ["Linnea Gräf <nea@nea.moe>", "Firmament Contributors"
 path = ["src/main/resources/legacy_data/*.json"]
 SPDX-License-Identifier = "MIT"
 SPDX-FileCopyrightText = ["PrismarineJS Minecraft Data"]
+
+[[annotations]]
+path = ["flake.lock"]
+SPDX-License-Identifier = "CC0-1.0"
+SPDX-FileCopyrightText = ["Auto Generated"]

flake.lock

@@ -0,0 +1,42 @@
+# SPDX-FileCopyrightText: 2026 Linnea Gräf <nea@nea.moe>
+#
+# SPDX-License-Identifier: GPL-3.0-or-later
+{
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+    flake-utils.url = "github:numtide/flake-utils";
+
+    treefmt-nix.url = "github:numtide/treefmt-nix";
+    treefmt-nix.inputs.nixpkgs.follows = "nixpkgs";
+  };
+  outputs =
+    inputs@{
+      treefmt-nix,
+      flake-utils,
+      self,
+      nixpkgs,
+      ...
+    }:
+    let
+      overlays = [
+      ];
+    in
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit overlays system; };
+        treefmtEval =
+          (treefmt-nix.lib.evalModule pkgs {
+            projectRootFile = "flake.nix";
+            imports = [ ];
+            programs.nixfmt.enable = true;
+          }).config.build;
+      in
+      {
+        formatter = treefmtEval.wrapper;
+        checks.formatting = treefmtEval.check self;
+        devShells.default = import ./shell.nix { inherit pkgs; };
+      }
+    );
+}