`makePersisted()` cannot correctly infer types under Typescript 7

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
55/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Quiet
Tech stack
typescript
Domain
developer-experience

Research direction

Start at the makePersisted entry point and reproduce the inferred-type failure from src/App.tsx using the linked StackBlitz example. Run tsc --noEmit with the createSignal("hello") call and compare it with the explicit generic version. Done means the inferred call type-checks without requiring explicit types.

Written by the indexing model from the issue text.

Description

bug
Describe the bug
const [thing, setThing] = makePersisted(createSignal("hello"), {
    name: "thing",
    storage: localStorage,
});

> tsc --noEmit

src/App.tsx(8,43): error TS2769: No overload matches this call.
  The last overload gave the following error.
    Argument of type 'Signal<string>' is not assignable to parameter of type 'Signal<unknown> | [unknown, SetStoreFunction<unknown>]'.
      Type '[get: Accessor<string>, set: Setter<string>]' is not assignable to type 'Signal<unknown>'.
        Type at position 1 in source is not compatible with type at position 1 in target.
          Type 'Setter<string>' is not assignable to type 'Setter<unknown>'.
            Target signature provides too few arguments. Expected 1 or more, but got 0.

Currently, the only way to fix it seems to be to provide full, explicit types:

const [thing, setThing] = makePersisted<string, Signal<string>>(createSignal("hello"), {
    name: "thing",
    storage: localStorage,
});
Minimal Reproduction Link

https://stackblitz.com/edit/github-ojctyhmm

Dominant language
TypeScript
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Merged PRs (30d)
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