add guix installer workflow

.forgejo/workflows/installer.yaml

@@ -0,0 +1,33 @@
+# title: install
+# desc: generate a guix installer image
+# adapted from https://github.com/SystemCrafters/guix-installer/
+
+name: installer
+on: [push]
+jobs:
+  build:
+    runs-on: docker
+    steps:
+      - name: Git checkout
+        uses: actions/checkout@v4
+
+      - name: Guix cache
+        uses: actions/cache@v4
+        with:
+          path: ~/.cache/guix
+          key: guix-cache-${{ github.sha }}
+          restore-keys: |
+            guix-cache
+
+      - name: Install Guix
+        uses: https://github.com/PromyLOPh/guix-install-action@v1.5
+
+      - name: Build ISO
+        run: |
+          ./scripts/build-installer
+
+      - name: Save artifact
+        uses: actions/upload-artifact@v4
+        with:
+          name: installer
+          path: guix-installer-*.iso

scripts/build-installer

@@ -3,7 +3,7 @@ retry="$(dirname $0)/guix-retry"
 repo="$(realpath "$(dirname $0)/..")"
 extra_args=""
 
-if [ ! -d /gnu/store ]; then
+if [ -f /usr/local/bin ]; then
 # we are likely in a non guix system
 # just for building the installer
 # make sure to authorize the substitute