flake: add nix-github-actions for running checks in GitHub actions

.github/workflows/build-checks.yml

@@ -0,0 +1,43 @@
+name: "Nix flake checks"
+
+on:
+  pull_request:
+  push:
+
+permissions:
+  contents: read
+
+jobs:
+  nix-matrix:
+    runs-on: ubuntu-latest
+    outputs:
+      matrix: ${{ steps.set-matrix.outputs.matrix }}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - uses: cachix/install-nix-action@3715ab1a11cac9e991980d7b4a28d80c7ebdd8f9 # v27
+      - id: set-matrix
+        name: Generate Nix checks matrix
+        run: |
+          set -Eeu
+          matrix="$(nix eval --json '.#githubActions.matrix')"
+          echo "matrix=$matrix" >> "$GITHUB_OUTPUT"
+
+  nix-build:
+    name: ${{ matrix.name }} (${{ matrix.system }})
+    needs: nix-matrix
+    runs-on: ${{ matrix.os }}
+    env:
+      CHECK_ATTR: ${{ matrix.attr }}
+    strategy:
+      matrix: ${{fromJSON(needs.nix-matrix.outputs.matrix)}}
+    steps:
+      - uses: actions/checkout@11bd71901bbe5b1630ceea73d27597364c9af683 # v4.2.2
+        with:
+          persist-credentials: false
+      - uses: cachix/install-nix-action@3715ab1a11cac9e991980d7b4a28d80c7ebdd8f9 # v27
+      - uses: DeterminateSystems/magic-nix-cache-action@87b14cf437d03d37989d87f0fa5ce4f5dc1a330b # v8
+        with:
+          diagnostic-endpoint: ""
+      - run: nix build -L ".#${CHECK_ATTR}"

flake.nix

@@ -16,12 +16,17 @@
       url = "github:minijackson/sphinxcontrib-nixdomain";
       inputs.nixpkgs.follows = "nixpkgs";
     };
+    nix-github-actions = {
+      url = "github:nix-community/nix-github-actions";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
 
   outputs = {
     self,
     flake-utils,
     nixpkgs,
+    nix-github-actions,
     ...
   } @ inputs: let
     overlay = import ./pkgs self.lib inputs;
@@ -129,5 +134,7 @@
       defaultTemplate = self.templates.default;
 
       formatter.x86_64-linux = nixpkgs.legacyPackages.x86_64-linux.alejandra;
+
+      githubActions = nix-github-actions.lib.mkGithubMatrix {inherit (self) checks;};
     };
 }