ThrottleTime with immediate output but all events must be n ms apart

[trungphan]

Feature Request

Is your feature request related to a problem? Please describe.
With the current throttleTime behavior with config {leading: true, trailing: true}, events are not guaranteed n ms apart. For example:

const observable = cold('-abcdef-----abcdef|');
const throttled = observable.pipe(
    throttleTime(time('---|'), getTestScheduler(), {leading: true, trailing: true}));
getTestScheduler().expectObservable(throttled).toBe('-a--de--f---a--de-(f|)');

Describe the solution you'd like
I want all events to be at least n ms apart. Specifically:

const observable = cold('-abcdef-----abcdef|');
const throttled = observable.pipe(
    throttleTime(time('---|'), getTestScheduler(), someFooConfig));
getTestScheduler().expectObservable(throttled).toBe('-a--d--f----a--d--(f|)');

Describe alternatives you've considered
I'm currently using throttleTime with {leading: true, trailing: true}, but that's not ideal since my RPCs are not always n ms apart (causing them being throttled from the server). The default config {leading: true, trailing: false} does not cut it because some trailing events are missing. The config {leading: false, trailing: true} does not cut it either because I'd like to process the event immediately if possible.

(If this is new operator request) describe reason it should be core operator
This can be achieved in the user-land module by just clone the throttleTime code and does the fix myself in my code, but that's not very elegant.

Additional context
This feature seems to be the one requested in #1625 , but the fix did not achieve that objective.

[benlesh]

I can't tell if this is a bug with the current behavior, or it should be a new feature. IMO, something isn't "throttled" if two events can be fired in less time than the throttle. 🤔

[benlesh]

Discussed with the team... we will try to align this with whatever lodash is doing.

[cartant]

TBH, this seems related to #4429 - i.e. inspectTime is, AFAICT, what's being sought, here.