Set up Cargo and Nix project

.envrc

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+use flake
+
+if [ -f .env ]; then
+  dotenv .env
+fi

.gitignore

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+/target
+/.direnv
+/.env
+/.yoi
+/result

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "decodal"
+version = "0.1.0"

Cargo.toml

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+[package]
+name = "decodal"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]

devshell.nix

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+{ pkgs }:
+pkgs.mkShell {
+  packages = with pkgs; [
+    cargo
+    clippy
+    git
+    nixfmt
+    rustc
+    rustfmt
+  ];
+
+  shellHook = ''
+    echo "decodal dev shell"
+  '';
+}

flake.lock

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+{
+  "nodes": {
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1731533236,
+        "narHash": "sha256-l0KFg5HjrsfsO/JpG+r7fRrqm12kzFHyUHqHCVpMMbI=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "11707dc2f618dd54ca8739b309ec4fc024de578b",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1781074563,
+        "narHash": "sha256-md8WlXOlfnIeHeOScMTTHFyf2d6iaTwPl2apR5EQ3P4=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "9ae611a455b90cf061d8f332b977e387bda8e1ca",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "flake-utils": "flake-utils",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "systems": {
+      "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

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+{
+  description = "Decodal - Deferred Constraint Data Language";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = nixpkgs.legacyPackages.${system};
+        decodal = pkgs.callPackage ./package.nix { };
+        mkApp = name: description: {
+          type = "app";
+          program = "${decodal}/bin/${name}";
+          meta.description = description;
+        };
+      in
+      {
+        packages.default = decodal;
+        packages.decodal = decodal;
+
+        apps.default = mkApp "decodal" "Run Decodal";
+        apps.decodal = mkApp "decodal" "Run Decodal";
+
+        checks.default = decodal;
+
+        devShells.default = import ./devshell.nix { inherit pkgs; };
+      }
+    );
+}

package.nix

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+{
+  lib,
+  rustPlatform,
+}:
+
+let
+  srcRoot = ./.;
+  srcRootString = toString srcRoot;
+  sourceFilter =
+    path: type:
+    let
+      pathString = toString path;
+      relPath = lib.removePrefix "${srcRootString}/" pathString;
+      baseName = baseNameOf pathString;
+      isExcludedTree = dir: relPath == dir || lib.hasPrefix "${dir}/" relPath;
+    in
+    !(
+      baseName == ".git"
+      || baseName == "target"
+      || baseName == "result"
+      || isExcludedTree ".yoi"
+      || isExcludedTree ".worktree"
+    );
+in
+rustPlatform.buildRustPackage {
+  pname = "decodal";
+  version = "0.1.0";
+
+  src = lib.cleanSourceWith {
+    src = srcRoot;
+    filter = sourceFilter;
+  };
+
+  cargoLock.lockFile = ./Cargo.lock;
+
+  strictDeps = true;
+
+  doInstallCheck = true;
+  installCheckPhase = ''
+    runHook preInstallCheck
+
+    test -x "$out/bin/decodal"
+    "$out/bin/decodal" >/dev/null
+
+    runHook postInstallCheck
+  '';
+
+  meta = {
+    description = "Deferred Constraint Data Language";
+    license = lib.licenses.mit;
+    mainProgram = "decodal";
+    platforms = lib.platforms.unix;
+  };
+}

src/main.rs

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+fn main() {
+    println!("Hello, world!");
+}