[Martin Ferret (MartinFerret)]

Fixes #2084

Scheduler.postTask() currently returns Promise<any> and its callback is typed SchedulerPostTaskCallback with signature (): any, so the type of the callback's result is lost.

This makes both generic, through inputfiles/overridingTypes.jsonc only:

interface SchedulerPostTaskCallback<T = any> {
    (): T | PromiseLike<T>;
}
postTask<T = any>(callback: SchedulerPostTaskCallback<T>, options?: SchedulerPostTaskOptions): Promise<T>;

The callback returns T | PromiseLike<T> because postTask() resolves its promise with the callback's result, so an async callback is unwrapped: postTask(async () => "done") gives Promise<string>. This follows the existing TransformerFlushCallback pattern. T defaults to any, like structuredClone<T = any>, so references to SchedulerPostTaskCallback without a type argument keep compiling.

Behavior change: the result type is now inferred from the callback instead of any. The code that relied on the any result (for example assigning await scheduler.postTask(() => 42) to a string) now gets a type error. That is the only change.

Added unittests/files/schedulerPostTask.ts which checks the result types exactly and fails with the override reverted.

Hope this is ok! 😊

[github-actions]

Thanks for the PR!

This section of the codebase is owned by Kagami Sascha Rosylight (@saschanaz) - if they write a comment saying "LGTM" then it will be merged.

[Kagami Sascha Rosylight (saschanaz)]

There are variations of this already in other tests, we should have a shared definition...

[Martin Ferret (MartinFerret)]

You're right about the shared definition. I'd be happy to follow up with a PR going that way, are you OK with that?

[Kagami Sascha Rosylight (saschanaz)]

Looks reasonable, thanks! LGTM

[github-actions]

Merging because Kagami Sascha Rosylight (@saschanaz) is a code-owner of all the changes - thanks!