fix(timeout): no longer will timeout when receiving the first value synchronously (#6865)

* fix(timeout): do not timeout if source emits synchronously when subscribed Closes #6862 * chore: Improve comments * chore: minor test cleanup * chore: minor test cleanup * chore: Fix broken test that I broke! lol Co-authored-by: Ben Lesh <ben@benlesh.com>

Author: danielwiehl

spec/operators/timeout-spec.ts

@@ -1,8 +1,8 @@
 /** @prettier */
 import { expect } from 'chai';
-import { timeout, mergeMap, take } from 'rxjs/operators';
+import { timeout, mergeMap, take, concatWith } from 'rxjs/operators';
 import { TestScheduler } from 'rxjs/testing';
-import { TimeoutError, of, Observable } from 'rxjs';
+import { TimeoutError, of, Observable, NEVER } from 'rxjs';
 import { observableMatcher } from '../helpers/observableMatcher';
 
 /** @test {timeout} */
@@ -691,6 +691,15 @@ describe('timeout operator', () => {
  expectSubscriptions(inner.subscriptions).toBe([]);
  });
  });
+
+ it('should not timeout if source emits synchronously when subscribed', () => {
+ rxTestScheduler.run(({ expectObservable, time }) => {
+ const source = of('a').pipe(concatWith(NEVER));
+ const t = time(' ---|');
+ const expected = 'a---';
+ expectObservable(source.pipe(timeout({ first: new Date(t) }))).toBe(expected);
+ });
+ });
  });
 
  it('should stop listening to a synchronous observable when unsubscribed', () => {

src/internal/operators/timeout.ts

@@ -386,10 +386,12 @@ export function timeout<T, O extends ObservableInput<any>, M>(
  );
 
  // Intentionally terse code.
+ // If we've `seen` a value, that means the "first" clause was met already, if it existed.
+ // it also means that a timer was already started for "each" (in the next handler above).
  // If `first` was provided, and it's a number, then use it.
  // If `first` was provided and it's not a number, it's a Date, and we get the difference between it and "now".
  // If `first` was not provided at all, then our first timer will be the value from `each`.
- startTimer(first != null ? (typeof first === 'number' ? first : +first - scheduler!.now()) : each!);
+ !seen && startTimer(first != null ? (typeof first === 'number' ? first : +first - scheduler!.now()) : each!);
  });
 }