tests: lint the packer config in CI

.github/workflows/lint.yml

@@ -34,6 +34,21 @@ jobs:
           config: '.github/linters/.markdown-lint.yml'
           args: './README.md'
 
+  packer:
+    name: packer
+    runs-on: ubuntu-20.04
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v3
+      - name: Setup packer
+        uses: hashicorp/setup-packer@main
+        with:
+          version: latest
+      - name: Run packer init
+        run: "make image/init/digitalocean"
+      - name: Run `packer validate`
+        run: "make image/validate/digitalocean"
+
   shellcheck:
     name: shellcheck
     runs-on: ubuntu-20.04

package.mk

@@ -1,3 +1,7 @@
+ifndef PKR_VAR_dokku_version
+	PKR_VAR_dokku_version = $(shell grep Version debian/control | cut -d' ' -f2)
+endif
+
 /tmp/build-dokku/var/lib/dokku/GIT_REV:
 	mkdir -p /tmp/build-dokku
 	mkdir -p /tmp/build-dokku/usr/share/bash-completion/completions
@@ -31,3 +35,10 @@ ifdef DOKKU_GIT_REV
 else
 	git rev-parse HEAD > /tmp/build-dokku/var/lib/dokku/GIT_REV
 endif
+.PHONY: image/init/digitalocean
+image/init/digitalocean:
+	packer init contrib/images/digitalocean/packer.pkr.hcl
+
+.PHONY: image/validate/digitalocean
+image/validate/digitalocean:
+	packer validate -var 'dokku_version=${PKR_VAR_dokku_version}' contrib/images/digitalocean/packer.pkr.hcl