feat: add nix github workflow

Signed-off-by: Brian McGee <[email protected]>

.github/workflows/nix.yml

@@ -0,0 +1,36 @@
+name: Nix Flake Actions
+on:
+    push:
+        branches:
+            - main
+    pull_request:
+    workflow_dispatch:
+
+jobs:
+    nix-matrix:
+        runs-on: ubuntu-latest
+        outputs:
+            matrix: ${{ steps.set-matrix.outputs.matrix }}
+        steps:
+            - uses: actions/checkout@v4
+            - uses: cachix/install-nix-action@v26
+            - id: set-matrix
+              name: Generate Nix Matrix
+              run: |
+                  set -Eeu
+                  matrix="$(nix eval --json '.#githubActions.matrix')"
+                  echo "matrix=$matrix" >> "$GITHUB_OUTPUT"
+
+    nix-build:
+        needs: nix-matrix
+        runs-on: ${{ matrix.os }}
+        strategy:
+            matrix: ${{fromJSON(needs.nix-matrix.outputs.matrix)}}
+        steps:
+            - uses: actions/checkout@v4
+            - uses: cachix/install-nix-action@v26
+            - uses: cachix/cachix-action@v14
+              with:
+                  name: numtide
+                  authToken: "${{ secrets.CACHIX_AUTH_TOKEN }}"
+            - run: nix build -L ".#${{ matrix.attr }}"

flake.nix

@@ -3,7 +3,10 @@
 
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
-    flake-parts.url = "github:hercules-ci/flake-parts";
+    flake-parts = {
+      url = "github:hercules-ci/flake-parts";
+      inputs.nixpkgs-lib.follows = "nixpkgs";
+    };
     treefmt-nix = {
       # todo switch back to numtide/treefmt-nix once merged
       url = "github:brianmcgee/treefmt-nix/feat/pipelines";
@@ -16,10 +19,14 @@
     gomod2nix = {
       url = "github:nix-community/gomod2nix";
       inputs.nixpkgs.follows = "nixpkgs";
-      inputs.flake-utils.follows ="devshell/flake-utils";
+      inputs.flake-utils.follows = "devshell/flake-utils";
     };
     nix-filter.url = "github:numtide/nix-filter";
     flake-compat.url = "github:nix-community/flake-compat";
+    nix-github-actions = {
+      url = "github:nix-community/nix-github-actions";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs = inputs @ {flake-parts, ...}:

nix/checks.nix

@@ -1,5 +1,16 @@
-{lib, ...}: {
+{
+  lib,
+  inputs,
+  self,
+  ...
+}: {
+  # generate github actions matrix using the flake's checks
+  flake.githubActions = inputs.nix-github-actions.lib.mkGithubMatrix {
+    checks = lib.getAttrs ["x86_64-linux" "x86_64-darwin"] self.checks;
+  };
+
   perSystem = {self', ...}: {
+    # mixin every package
     checks = with lib; mapAttrs' (n: nameValuePair "package-${n}") self'.packages;
   };
 }