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fix: correctly check "undefined" as response body type #1824

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merged 2 commits into from
Nov 4, 2023
Merged

fix: correctly check "undefined" as response body type #1824

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40f026f
fix: correctly check "never" as response body type
kettanaito Nov 1, 2023
a31d097
Merge branch 'main' into fix/resolver-return-never
kettanaito Nov 4, 2023
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4 changes: 2 additions & 2 deletions src/core/handlers/RequestHandler.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -30,7 +30,7 @@ export interface RequestHandlerInternalInfo {
export type ResponseResolverReturnType<
BodyType extends DefaultBodyType = undefined,
> =
| (BodyType extends undefined ? Response : StrictResponse<BodyType>)
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T extends undefined is not the correct way to check if a generic was provided in TypeScript. Instead, one must resort to a hack:

[T] extends [never] ? 'NOT PROVIDED' : 'PROVIDED'

The previous implementation was giving false positives, making the custom response body type and the body type in ResponseResolverReturnType incompatible.

| ([BodyType] extends [undefined] ? Response : StrictResponse<BodyType>)
| undefined
| void

Expand Down Expand Up @@ -265,7 +265,7 @@ export abstract class RequestHandler<

// Clone the previously stored response from the generator
// so that it could be read again.
return this.resolverGeneratorResult.clone()
return this.resolverGeneratorResult.clone() as StrictResponse<any>
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A bit hacky. Suggestions are welcome.

}

if (!this.resolverGenerator) {
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10 changes: 10 additions & 0 deletions test/typings/regressions/response-body-type.test-d.ts
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@@ -0,0 +1,10 @@
/**
* @see https://github.com/mswjs/msw/issues/1823
*/
import { http, Path, HttpResponse, DefaultBodyType } from 'msw'

function myHandler<CustomResponseBodyType extends DefaultBodyType>(path: Path) {
return (response: CustomResponseBodyType) => {
http.get(path, () => HttpResponse.json(response))
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Also adding a typing regression test to make sure this doesn't happen again.

}
}
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