Revert "flake: switch to flake-parts"

This reverts commit 09c128c.

flake.nix

@@ -2,37 +2,43 @@
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
     flake-utils.url = "github:numtide/flake-utils";
-    flake-parts = {
-      url = "github:hercules-ci/flake-parts";
-      inputs.nixpkgs-lib.follows = "nixpkgs";
-    };
-    nci = {
-      url = "github:yusdacra/nix-cargo-integration";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
       inputs.nixpkgs.follows = "nixpkgs";
+      inputs.flake-utils.follows = "flake-utils";
     };
   };
 
-  outputs = inputs @ { flake-parts, flake-utils, ... }:
-    flake-parts.lib.mkFlake { inherit inputs; } {
-      systems = flake-utils.lib.defaultSystems;
-      imports = [ inputs.nci.flakeModule ];
-      perSystem = { config, pkgs, ... }:
-        let outputs = config.nci.outputs.rq;
-        in {
-          nci = {
-            toolchainConfig = ./rust-toolchain.toml;
-            projects.rq-project = {
-              path = ./.;
+  outputs = { self, nixpkgs, rust-overlay, flake-utils, ... }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        overlays = [ rust-overlay.overlays.default ];
+        pkgs = import nixpkgs { inherit system overlays; };
+        toolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+        platform = pkgs.makeRustPlatform {
+          cargo = toolchain;
+          rustc = toolchain;
+        };
+        cargoMeta =
+          (builtins.fromTOML (builtins.readFile ./Cargo.toml)).package;
+      in with pkgs; {
+        packages = {
+          rq = platform.buildRustPackage {
+            pname = "rq";
+            inherit (cargoMeta) version;
+            src = ./.;
+            meta = {
+              license = lib.licenses.gpl3;
+              description =
+                "a tiny functional language with which you can manipulate JSON";
             };
-            crates.rq = { };
-          };
-
-          packages = rec {
-            rq = outputs.packages.release;
-            default = rq;
+            cargoLock.lockFile = ./Cargo.lock;
           };
 
-          devShells.default = outputs.devShell;
+          default = self.packages."${system}".rq;
         };
-    };
+
+        devShells.default =
+          mkShell { buildInputs = [ toolchain rust-analyzer ]; };
+      });
 }

src/main.rs

@@ -3,6 +3,7 @@
 #![allow(confusable_idents)]
 #![feature(assert_matches)]
 #![feature(box_patterns)]
+#![feature(extend_one)]
 #![feature(iter_intersperse)]
 #![feature(lazy_cell)]
 #![feature(slice_split_once)]