Add CI and cache

.github/workflows/ci.yml

@@ -0,0 +1,82 @@
+name: CI
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  checks:
+    runs-on: ubuntu-latest
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v24
+
+      - name: Nix Format Check
+        run: nix fmt -- . --check
+
+      - name: Nix Syntax Check
+        run: nix flake check
+
+  build-plan:
+    # Save some computation. If the checks fail, don't build.
+    needs: checks
+    runs-on: ubuntu-latest
+    outputs:
+      attrs: ${{ steps.plan.outputs.ATTRS }}
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v24
+        with:
+          nix_path: nixpkgs=channel:nixos-23.11
+
+      - name: Build and Cache Attic
+        if: github.event_name != 'pull_request'
+        run: |
+          nix profile install github:zhaofengli/attic#attic
+          attic login --set-default lowrisc https://nix-cache.lowrisc.org/ ${{ secrets.NIX_CACHE_TOKEN }}
+          attic push public $(which attic)
+
+      - name: Generate Nix Build Plan
+        id: plan
+        run: |
+          echo 'ATTRS<<EOF' >> $GITHUB_OUTPUT
+          nix-shell -p nix-eval-jobs --run 'nix-eval-jobs --accept-flake-config --check-cache-status --flake .#packages.x86_64-linux' | \
+            tee /dev/stderr | \
+            jq -s 'map(select(.isCached | not) | .attr)' | \
+            tee -a $GITHUB_OUTPUT
+          echo 'EOF' >> $GITHUB_OUTPUT
+
+  build:
+    needs: build-plan
+    runs-on: ${{ matrix.os }}
+    strategy:
+      matrix:
+        attr: ${{fromJSON(needs.build-plan.outputs.attrs)}}
+    steps:
+      - name: checkout
+        uses: actions/checkout@v4
+
+      - name: Install Nix
+        uses: cachix/install-nix-action@v24
+
+      - name: Setup Cache
+        if: github.event_name != 'pull_request'
+        run: |
+          nix profile install github:zhaofengli/attic#attic
+          attic login --set-default lowrisc https://nix-cache.lowrisc.org/ ${{ secrets.NIX_CACHE_TOKEN }}
+
+      - name: Build
+        run: nix build ".#${{ matrix.attr }}" --accept-flake-config
+
+      - name: Upload Cache
+        if: github.event_name != 'pull_request'
+        run: |
+          attic push public result/

flake.nix

@@ -14,6 +14,12 @@
       inputs.flake-utils.follows = "flake-utils";
     };
   };
+
+  nixConfig = {
+    extra-substituters = ["https://nix-cache.lowrisc.org/public/"];
+    extra-trusted-public-keys = ["public:O6JLD0yXzaJDPiQW1meVu32JIDViuaPtGDfjlOopU7o="];
+  };
+
   outputs = {
     self,
     nixpkgs,