fix(types): extends check of generic in WithSdkStreamMixin

[Lewenhaupt]

Fix an issue where WithSdkStreamMixin would apply to more properties than intended due to Distributive Conditional Types.

Issue

#4111

Description

Fix an issue where WithSdkStreamMixin would apply to more properties than intended due to Distributive Conditional Types.

Testing

Tested locally with client-s3 and it's GetObjectCommand-output which now correctly only applies the mixin on "Body".

---

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[Lewenhaupt]

@trivikr Does your builds get cached? Seems it's the same build.

Is the title better now?

[kuhe]

Suggested change

	[key in keyof T]: [T[key]] extends [T[StreamKey]] ? SdkStream<T[StreamKey]> : T[key];
	[key in keyof T]: key extends StreamKey ? SdkStream<T[StreamKey]> : T[key];

[kuhe]

type Stream = {} | undefined;

type Data = {
    undef: undefined
    num: number
    str: string
    stream: Stream
}

type Mixin<T> = T & {
    someAddedMethod(): void
}

// for v1/v2, the match is on the type of the key indicated. This is too wide if the Stream type includes undefined.
type ApplyConditionalTypeMappingV1<T, Key extends keyof T> = {
    [key in keyof T]: T[key] extends T[Key] ? Mixin<T[Key]> : T[key];
}

type ApplyConditionalTypeMappingV2<T, Key extends keyof T> = {
    [key in keyof T]: [T[key]] extends [T[Key]] ? Mixin<T[Key]> : T[key];
}

// this applies the type mixin only to the specified key.
type ApplyConditionalTypeMappingV3<T, Key extends keyof T> = {
    [key in keyof T]: key extends Key ? Mixin<T[Key]> : T[key];
}

const data: ApplyConditionalTypeMappingV3<Data, 'stream'> = {
    num: 1,
    str: 'a',
    stream: undefined,
    undef: undefined,
}

[Lewenhaupt]

Agreed that this is more robust

[Lewenhaupt]

Updated docs, however this does change the behaviour and I'm not sure if the change from matching multiple keys to only a single key is expected (even though the signature of the mixin definitely indicates it only should match one key). But I'll leave that up to you maintainers :)

[kuhe]

Yes, there will only be one key. I believe this is guaranteed by Smithy.

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a new issue for related bugs and link to relevant comments in this thread.