Typescript const assertion shows as a syntax error Follow

I am using a const assertion (from TypeScript 3.4) in an Angular guard that works with an observable.  I have specified that the return type of the guard method return Observable<true | UrlTree> because I intend to have the guard method either return true based on a value from some service or return an UrlTree in case of an error, which instructs it to navigate to a different URL.  I came up with this code that the TypeScript compiler does not report an error on, but Resharper does:

if (someCondition) {
  return this.myService.myMethodThatReturnsAnObservable(aParameter)
             .pipe(
                   map(() => true as const),
                   catchError(error => { /* some code that returns an Observable<UrlTree> */),
                   // etc.
             );
} else {
  // other logic
}

Resharper shows a red squiggly after "as" saying Type name expected.  It also dims out everything after the as to the closing brace of the pipe() and reports "Code is unreachable" and "; is expected" after the "const".  It also shows further errors after the pipe().

Are const assertions something that Resharper doesn't currently support?

(Sorry, I did not know which Topic to choose.)