github.com/jthegedus/firebase-gcp-examples/tree/master/functions-nextjs

firebase-functions.json

{
  ...
  "functions": {
    "source": ".",
    "ignore": [
      "firebase.json",
      "firbease-debug.log",
      "**/.*",
      "**/node_modules/**",
      "components/**",
      "helpers/**",
      "out/**",
      "pages/**",
      "public/**",
      "scripts/**",
      "firestore.rules",
      "readme.md"
    ]
  },
  ...
}