nix: initial tooling

.envrc

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+use flake
+

flake.lock

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+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1752950548,
+        "narHash": "sha256-NS6BLD0lxOrnCiEOcvQCDVPXafX1/ek1dfJHX1nUIzc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c87b95e25065c028d31a94f06a62927d18763fdf",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

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+{
+  description = "Rust Project Template";
+  inputs.nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+
+  outputs = {
+    self,
+    nixpkgs,
+  }: let
+    systems = ["x86_64-linux" "aarch64-linux"];
+    forEachSystem = nixpkgs.lib.genAttrs systems;
+
+    pkgsForEach = nixpkgs.legacyPackages;
+  in {
+    packages = forEachSystem (system: {
+      default = pkgsForEach.${system}.callPackage ./nix/package.nix {};
+    });
+
+    devShells = forEachSystem (system: {
+      default = pkgsForEach.${system}.callPackage ./nix/shell.nix {};
+    });
+
+    hydraJobs = self.packages;
+  };
+}

nix/package.nix

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+{
+  lib,
+  rustPlatform,
+}:
+rustPlatform.buildRustPackage (finalAttrs: {
+  pname = "eh";
+  version = (builtins.fromTOML (builtins.readFile ../Cargo.toml)).workspace.package.version;
+
+  src = let
+    fs = lib.fileset;
+    s = ../.;
+  in
+    fs.toSource {
+      root = s;
+      fileset = fs.unions (map (dir: (s + /${dir})) [
+        ".cargo"
+        "eh"
+        "xtask"
+        "Cargo.toml"
+        "Cargo.lock"
+      ]);
+    };
+
+  cargoLock.lockFile = "${finalAttrs.src}/Cargo.lock";
+  enableParallelBuilding = true;
+
+  meta = {
+    description = "Ergonomic Nix CLI helper";
+    maintainers = with lib.licenses; [NotAShelf];
+  };
+})

nix/shell.nix

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+{
+  mkShell,
+  rust-analyzer,
+  rustfmt,
+  clippy,
+  cargo,
+  rustPlatform,
+}:
+mkShell {
+  name = "rust";
+  packages = [
+    rust-analyzer
+    rustfmt
+    clippy
+    cargo
+  ];
+
+  RUST_SRC_PATH = "${rustPlatform.rustLibSrc}";
+}