Inexact optional property types

[iwoplaza]

Environment

• unplugin: 6.2.2
• typescript: 5.7.2

Reproduction

https://stackblitz.com/edit/vitejs-vite-lovdzaug?file=unplugin-foo.ts

Describe the bug

Definitions like:

type StringFilter = FilterPattern | {
	include?: FilterPattern
	exclude?: FilterPattern
};

... can cause friction when using the TypeScript exactOptionalPropertyTypes compiler option, since under that configuration, undefined is not a valid value to be passed into include or exclude. Would it break anything to widen the type to the following?:

type StringFilter = FilterPattern | {
	include?: FilterPattern | undefined
	exclude?: FilterPattern | undefined
};

Additional information

• Would you be willing to help implement a patch for this?

[sxzz]

/cc @antfu WDYT

[iwoplaza]

Bumping this for visibility 👀

[antfu]

I would need more explanations about why exactOptionalPropertyTypes is useful and what benefit it provides. As the option is not enabled by default in TypeScript, I believe the majority of the packages on npm are not following this pattern, which makes this change feel a bit less effective.

[iwoplaza]

Sorry for the late response. I was going to base my argument on "optimizing for strictness makes it compatible for both strict and non-strict setups", which is still true, but TypeScript recently made exactOptionalPropertyTypes true by default when running tsc --init: microsoft/TypeScript#61813

Still, typing everything explicitly as foo?: T | undefined is interpreted the same in a "strict" and a "non-strict" setup, while foo? T is interpreted differently based on the end user's tsconfig