feat: Add Nix flake (#52)

* feat: Add Nix flake

* Simplify Nix build

Author: samuelburnham

.github/workflows/ci.yml

@@ -1,14 +1,36 @@
-name: "CI"
+name: CI Tests
+
 on:
-  pull_request:
   push:
-    branches:
-      - main
+    branches: main
+  pull_request:
+  workflow_dispatch:
+
+concurrency:
+  group: ${{ github.workflow }}-${{ github.head_ref || github.run_id }}
+  cancel-in-progress: true
+
 jobs:
-  build:
+  lean:
+    name: Lean Build
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: leanprover/lean-action@v1
         with:
           build-args: "--wfail"
+
+  nix:
+    name: Nix Flake Check
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: cachix/install-nix-action@v30
+        with:
+          nix_path: nixpkgs=channel:nixos-unstable
+          github_access_token: ${{ secrets.GITHUB_TOKEN }}
+      - uses: cachix/cachix-action@v14
+        with:
+          name: argumentcomputer
+          authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
+      - run: nix build

.gitignore

@@ -1,3 +1,4 @@
 /build
 /lake-packages
 .lake/
+/result*

flake.lock

@@ -0,0 +1,51 @@
+{
+  description = "LSpec Nix Flake";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    lean4-nix = {
+      url = "github:argumentcomputer/lean4-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs = inputs @ {
+    nixpkgs,
+    flake-parts,
+    lean4-nix,
+    ...
+  }:
+    flake-parts.lib.mkFlake {inherit inputs;} {
+      systems = [
+        "aarch64-darwin"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "x86_64-linux"
+      ];
+
+      perSystem = {
+        system,
+        pkgs,
+        self',
+        config,
+        ...
+      }:
+      {
+        _module.args.pkgs = import nixpkgs {
+          inherit system;
+          overlays = [(lean4-nix.readToolchainFile ./lean-toolchain)];
+        };
+
+        # Build the library with `nix build`
+        packages.default = ((lean4-nix.lake {inherit pkgs;}).mkPackage {
+            src = ./.;
+            roots = ["LSpec"];
+        }).modRoot;
+
+        devShells.default = pkgs.mkShell {
+          packages = with pkgs.lean; [lean lean-all];
+        };
+    };
+  };
+}