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Fix createResource initial value inference #2696

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Fix createResource initial value inference #2696

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16 changes: 8 additions & 8 deletions packages/solid/src/reactive/signal.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -577,19 +577,19 @@ function isPromise(v: any): v is Promise<any> {
*
* @description https://docs.solidjs.com/reference/basic-reactivity/create-resource
*/
export function createResource<T, R = unknown>(
fetcher: ResourceFetcher<true, T, R>,
options: InitializedResourceOptions<NoInfer<T>, true>
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@le0-0 le0-0 May 14, 2026

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Could the problem be resolved by just removing the NoInfer of the T in the InitializedResourceOptions here? In that way, what goes on inside there can contribute to the type T. This would be cleaner than the parallel I mechanism if it works.

): InitializedResourceReturn<T, R>;
export function createResource<T, R = unknown, I = T>(
fetcher: (k: true, info: ResourceFetcherInfo<T | I, R>) => T | Promise<T>,
options: ResourceOptions<T | I, true> & { initialValue: I }
): InitializedResourceReturn<T | I, R>;
export function createResource<T, R = unknown>(
fetcher: ResourceFetcher<true, T, R>,
options?: ResourceOptions<NoInfer<T>, true>
): ResourceReturn<T, R>;
export function createResource<T, S, R = unknown>(
export function createResource<T, S, R = unknown, I = T>(
source: ResourceSource<S>,
fetcher: ResourceFetcher<S, T, R>,
options: InitializedResourceOptions<NoInfer<T>, S>
): InitializedResourceReturn<T, R>;
fetcher: (k: S, info: ResourceFetcherInfo<T | I, R>) => T | Promise<T>,
options: ResourceOptions<T | I, S> & { initialValue: I }
): InitializedResourceReturn<T | I, R>;
export function createResource<T, S, R = unknown>(
source: ResourceSource<S>,
fetcher: ResourceFetcher<S, T, R>,
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30 changes: 30 additions & 0 deletions packages/solid/test/resource.type-tests.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,21 @@ type Equals<X, Y> =
type Tests = Assert<Equals<ResourceActions["mutate"], Setter<number>>>;
}

// without source
// with fetcher, nullable initialValue
{
const resourceReturn = createResource(
() => {
return Promise.resolve(1);
},
{
initialValue: null
}
);

type Tests = Assert<Equals<typeof resourceReturn, InitializedResourceReturn<number | null>>>;
}

// without initialValue
// with source, fetcher
{
Expand Down Expand Up @@ -105,6 +120,21 @@ type Equals<X, Y> =
);
}

// with source, fetcher, nullable initialValue
{
const resourceReturn = createResource(
() => 1,
() => {
return Promise.resolve(1);
},
{
initialValue: null
}
);

type Tests = Assert<Equals<typeof resourceReturn, InitializedResourceReturn<number | null>>>;
}

/* Resource type tests */
{
let resource!: Resource<string>;
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