flake: init with Rust devShell

flake.lock

@@ -0,0 +1,65 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1759070547,
+        "narHash": "sha256-JVZl8NaVRYb0+381nl7LvPE+A774/dRpif01FKLrYFQ=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "647e5c14cbd5067f44ac86b74f014962df460840",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs",
+        "rust-overlay": "rust-overlay",
+        "systems": "systems"
+      }
+    },
+    "rust-overlay": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1759199574,
+        "narHash": "sha256-w24RYly3VSVKp98rVfCI1nFYfQ0VoWmShtKPCbXgK6A=",
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "rev": "381776b12d0d125edd7c1930c2041a1471e586c0",
+        "type": "github"
+      },
+      "original": {
+        "owner": "oxalica",
+        "repo": "rust-overlay",
+        "type": "github"
+      }
+    },
+    "systems": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,35 @@
+{
+  description = "Noita Entangled Worlds";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+    systems = {
+      url = "github:nix-systems/default";
+      flake = false;
+    };
+  };
+
+  outputs = { self, nixpkgs, rust-overlay, systems, }:
+    let
+      inherit (nixpkgs) lib;
+      eachSystem = lib.genAttrs (import systems);
+      pkgsFor = eachSystem (system:
+        import nixpkgs {
+          localSystem = system;
+          overlays = [ self.overlays.default ];
+        });
+    in {
+      overlays = import ./nix/overlays { inherit self lib rust-overlay; };
+
+      devShells = lib.mapAttrs
+        (system: pkgs: { default = pkgs.callPackage ./nix/shell.nix { }; })
+        pkgsFor;
+
+      formatter =
+        eachSystem (system: nixpkgs.legacyPackages.${system}.nixfmt-classic);
+    };
+}

nix/overlays/default.nix

@@ -0,0 +1,14 @@
+{ self, lib, rust-overlay }: {
+  default = lib.composeManyExtensions [
+    # This is to ensure that other overlays and invocations of `callPackage`
+    # receive `rust-bin`, but without hard-coding a specific derivation.
+    # This can be overridden by consumers.
+    self.overlays.rust-overlay
+  ];
+
+  # This flake exposes `overlays.rust-overlay` which is automatically applied
+  # by `overlays.default`. This overlay is intended to provide `rust-bin` for
+  # the package overlay, in the event it is not already present.
+  rust-overlay = final: prev:
+    if prev ? rust-bin then { } else rust-overlay.overlays.default final prev;
+}

nix/shell.nix

@@ -0,0 +1,18 @@
+{ rust-bin, mkShell }:
+mkShell {
+  strictDeps = true;
+
+  packages = [
+    # Derivations in `rust-stable` provide the toolchain,
+    # must be listed first to take precedence over nightly.
+    (rust-bin.stable.latest.minimal.override {
+      extensions = [ "rust-src" "rust-docs" "clippy" ];
+    })
+
+    # Use rustfmt, and other tools that require nightly features.
+    (rust-bin.selectLatestNightlyWith (toolchain:
+      toolchain.minimal.override {
+        extensions = [ "rustfmt" "rust-analyzer" ];
+      }))
+  ];
+}