Type-unsafe behavior of watch

[clemyan]

Version

3.0.0-alpha.5

Reproduction link

http://www.typescriptlang.org/v2/en/play?ts=3.7.5#code/JYWwDg9gTgLgBAbzlApgMwDRwO4EMYDGAFlgErpwC+caUEIcA5AAIBuArigPRTsB2MUCgC0BaCkYAoSWL4BneGjgBeOAAooALjjk0AHj7sQAIxRQAfHAA+cQybMBKFZYSS4cWQo8QzBFABMVZHQNBzccfGI1MV8ArDVWJ2UXcPcuLjgAUQAPFDAUAhhtVjhgOVsjUyhUuHS4AEFC9lwAG2LS8t0DSrNLGzsqms8IFpQAOhaIAHMEuABqOABGMPdKMMpJIA

Steps to reproduce

1. The typescript playground link shows error

What is expected?

v is of type number

What is actually happening?

v is of type Ref<number> | number

---

This overload of watch is typed as (simplified)

watch<T>(
  source: WatchSource<T>,
  cb: WatchCallback<T, T>
)

which is type-unsafe because if source is Ref<T>, source.value is UnwrapRef<T>, which cannot be passed to WatchCallback<T, T>.

TypeScript fails to catch the error since the underlying call doWatch is typed using any:

doWatch(
  source: WatchSource<any>,
  cb: WatchCallback<any, any>,
)

[yyx990803]

Seems to be a problem in ref's typing instead of watch, since the type of coerced should be Ref<number> instead of Ref<number | Ref<number>>.

[clemyan]

So you are saying ref should be typed as <T>(v: T) => Ref<UnwrapRef<T>>?

Oops, didn't see a commit closed this issue.

[clemyan]

I see this specific instance of the issue is fixed in alpha.6. However, I still think this is a problem with watch. As long as the value property of Ref<T> is typed as UnwrapRef<T>, it is not type-safe to treat ref.value as T and pass it to WatchCallback<T, T>.

Type-unsafe example

[yyx990803]

That's a good catch. I think ref value unwrapping should happen in its creation signature - see d4c6957