feat: verify that volumes are empty

This can cause problems in some setups and should not be needed as the
container expects these to be empty.

See WeblateOrg/docker#2816

Author: nijel

.github/workflows/dockerimage.yml

@@ -12,6 +12,8 @@ jobs:
 
     steps:
     - uses: actions/checkout@v4
+    - name: Test content
+      run: ./test-content
     - name: Generate configuration
       run: ./test-generate 8080 http
     - name: Startup container

test-content

@@ -0,0 +1,23 @@
+#!/bin/sh
+
+STORAGE=$(mktemp)
+cleanup(){
+    rm "$STORAGE"
+}
+trap cleanup EXIT
+
+echo "Creating container..."
+docker create --name="tmp_$$" "${TEST_CONTAINER:-weblate/weblate:edge}"
+echo "Listing content container..."
+docker export tmp_$$ | tar t > "$STORAGE"
+echo "Removing container..."
+docker rm tmp_$$
+echo "Checking content..."
+
+# /app/data is not checked because it contains stub for customization
+if grep -E '^(app/cache|tmp|run)/.+' "$STORAGE" ; then
+    echo "Volumes contain files!"
+    exit 1
+fi
+
+echo "$STORAGE"