**Description**

For a DAG that looks like this:

```
A >> B
```

If A fails, B goes into "upstream_failed" state. If a user then marks A "success", B will remain in "upstream_failed" state. It will not automatically start running. This scenario often happens if the failure of A is dealt with outside of Airflow and the user does not want Airflow to run A again. But he usually expect Airflow to run B after A is marked "success".

**Use case / motivation**

After A is marked "success", its downstream tasks B should be cleared automatically and get ready to be scheduled. To avoid changing this behaviour completely, there can be a toggle button next to "Success" that lets the user decide if he wants Airflow to automatically clear downstream tasks that are in "upstream_failed" state.
airflow/models/dag.py
new_start = self.previous_schedule(last_start)
            if self.start_date:
                if new_start >= self.start_date:
                    self.start_date = new_start
            else:
                self.start_date = new_start
        next_run_date = None
        if not date_last_automated_dagrun:
            
            task_start_dates = [t.start_date for t in self.tasks if t.start_date]
            if task_start_dates:
                next_run_date = self.normalize_schedule(min(task_start_dates))
                self.log.debug("Next run date based on tasks %s", next_run_date)
        else:
            next_run_date = self.following_schedule(date_last_automated_dagrun)
        if date_last_automated_dagrun and next_run_date:
            while next_run_date <= date_last_automated_dagrun:
                next_run_date = self.following_schedule(next_run_date)
        
        if self.start_date:
            next_run_date = self.start_date if not next_run_date else max(next_run_date, self.start_date)
            if next_run_date == self.start_date:
                next_run_date = self.normalize_schedule(self.start_date)
            self.log.debug("Dag start date: %s. Next run date: %s", self.start_date, next_run_date)
        
        if next_run_date and self.end_date and next_run_date > self.end_date:
            return None
        
        
        task_end_dates = [t.end_date for t in self.tasks if t.end_date]