Errors are squeltched when thrown in next, after any operator, while useDeprecatedSynchronousErrorHandling = true;

[benlesh]

In RxJS 7, if you set useDeprecatedSynchronousErrorHandling = true, and you have a source that uses any operator, when you throw an error in the next handler, it's not rethrown. The first example was with take, but I've confirmed it also happens with map, concatMap, and others.

https://stackblitz.com/edit/rxjs-fuauce?devtoolsheight=60

import { of, config } from "rxjs";
import { take } from "rxjs/operators";

console.clear();

config.useDeprecatedSynchronousErrorHandling = true;

try {
  of("test")
    .pipe(take(1))
    .subscribe({
      next: value => {
        console.log("value: ", value);
        throw new Error("test");
      }
    });
} catch (err) {
  // This is never hit in v7, but it is hit in v6.
  console.log("Caught!", err.message);
}

We'll need to check takeUntil, takeWhile, and first for the same issues.

cc @leggechr

[benlesh]

The apparent cause is that the new architecture "knows" that we don't synchronously rethrow in the common case. So when the error is synchronously rethrown, it unwinds the stack and is caught by the try-catch blocks in the OperatorSubscriber. We'll unfortunately need to work around this for the deprecated case. :\