feat(schema): add type hints for runtime config

[danielroe]

🔗 Linked issue

#18594 (comment)

❓ 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 adds type hints (within nuxt.config only, not within useRuntimeConfig) to advise on the way to override runtime config:

I would value some testing on this and improving the algorithm to make sure we are matching scule. (We might also move into scule itself if you like @pi0, and that way we could add more type tests there.)

BTW, I initially considered using https://github.com/sindresorhus/type-fest/blob/main/source/snake-case.d.ts but there were issues with it (e.g. baseURL and PascalCase both gave incorrect results) and I thought better to take a completely different approach.

▶️ TypeScript playground.

📝 Checklist

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

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[manniL]

Really nice DX 🔥

[pi0]

Since env handling logic is happening in Nitro, i think we could generate types also from nitro types. BTW really nice addition 🔥

[pi0]

For runtime consistency, we might also directly use scule (in build time) to generate precise types.

[danielroe]

Indeed, it might be nice to add a facility to generate TSDoc comments via a callback for generateTypes from untyped, meaning we could annotate directly in the declarations we generate. That would be guaranteed to be accurate and would be a more natural way of providing the help.

[Baroshem]

This is a really great feature! Cant wait to see it in the new version of nuxt 🙂

[danielroe]

merging as a first step - moving to tsdoc is definitely better performance-wise but will need to be implemented in https://github.com/unjs/untyped.