fix(nuxt): warn to provide a key for useFetch with transform option

[danielroe]

🔗 Linked issue

resolves nuxt/nuxt#13790

❓ Type of change

• 📖 Documentation (updates to the documentation or readme)
• 🐞 Bug fix (a non-breaking change that fixes an issue)
• 👌 Enhancement (improving an existing functionality like performance)
• ✨ New feature (a non-breaking change that adds functionality)
• ⚠️ Breaking change (fix or feature that would cause existing functionality to change)

📚 Description

This PR addresses two issues:

1. In production the transform function .toString() differs between server/client so the generated key (from ohash) doesn't match.
2. When there is a mismatch (no key in payload), then currently we just skip refreshing, when probably we want to re-fetch on client-side.

Other options:

1. generate a key at build-time from hash of transform function
2. exclude transform function from hash generation

It feels like the safest option is to require a user to provide a custom key in the event of using transform.

📝 Checklist

• I have linked an issue or discussion.
• I have updated the documentation accordingly.

[netlify]

✅ Deploy Preview for nuxt3-docs ready!

Name	Link
🔨 Latest commit	cdd83a5
🔍 Latest deploy log	https://app.netlify.com/sites/nuxt3-docs/deploys/626929bb42e6c700091a27ca
😎 Deploy Preview	https://deploy-preview-4590--nuxt3-docs.netlify.app
📱 Preview on mobile	Toggle QR Code... Use your smartphone camera to open QR code link.

---

To edit notification comments on pull requests, go to your Netlify site settings.

[pi0]

I think we can exclude options that are not related to fetch like transform from hash transformation. hashing it to distinguish by request.

[danielroe]

I think we can exclude options that are not related to fetch like transform from hash transformation. hashing it to distinguish by request.

I would say that transform should make a difference to the hash. Consider:

await useFetch('/api/test', { transform: data => data[0] })
await useFetch('/api/test')

These two calls will result in different data, and if we don't enforce a key generation then there's a danger of mismatching payloads.

[pi0]

Okay i'm fine with adding warning until find a better way for auto hashing. Can we in the meantime remove transform from hash when making warning?