compiler option to fallback to unknown instead of any when failing to resolve a type

[DetachHead]

Suggestion

🔍 Search Terms

unknown instead of any error

✅ Viability Checklist

My suggestion meets these guidelines:

• This wouldn't be a breaking change in existing TypeScript/JavaScript code
• This wouldn't change the runtime behavior of existing JavaScript code
• This could be implemented without emitting different JS based on the types of the expressions
• This isn't a runtime feature (e.g. library functionality, non-ECMAScript syntax with JavaScript output, new syntax sugar for JS, etc.)
• This feature would agree with the rest of TypeScript's Design Goals.

⭐ Suggestion

currently, when a type fails to resolve, there's an error in an external lib suppressed by skipLibCheck, or an error suppressed by @ts-expect-error/@ts-ignore, the type falls back to any

it would be nice if there was a compiler option that changes this behavior to unknown instead of any. it would make this feature even more useful too

📃 Motivating Example

currently, @ts-ignore and @ts-expect-error comments aren't exposed in .d.ts files. one of the concerns with changing this functionality seems to be that it can result in any leaking into the codebase (see #38628 (comment)).

💻 Use Cases

• makes it safer to use skipLibCheck, for example if a lib was compiled using a different version of typescript which causes errors on the version you're using
• makes it a little bit safer to use @ts-expect-error

[Silic0nS0ldier]

Type errors in libraries with unchecked types isn't the only place any can sneak in. If resolution is aborted (e.g. long lookup chain or bail-out triggered by a heuristic) any ends up being used instead. I've observed this happening on 2 occasions in the Canva source and wouldn't be surprised if more instances are hiding away.