remove deadline check in reset_at

tokio/src/time/interval.rs

@@ -583,7 +583,6 @@ impl Interval {
     }
 
     /// Resets the interval to a [`crate::time::Instant`] deadline.
-    /// If deadline is in the past it behaves like `reset_immediately`.
     ///
     /// This method ignores [`MissedTickBehavior`] strategy.
     ///
@@ -611,11 +610,7 @@ impl Interval {
     /// }
     /// ```
     pub fn reset_at(&mut self, deadline: Instant) {
-        if deadline > Instant::now() {
-            self.delay.as_mut().reset(deadline);
-        } else {
-            self.reset_immediately();
-        }
+        self.delay.as_mut().reset(deadline);
     }
 
     /// Returns the [`MissedTickBehavior`] strategy currently being used.

tokio/tests/time_interval.rs

@@ -275,6 +275,42 @@ async fn reset_after() {
     check_interval_poll!(i, start, 721);
 }
 
+#[tokio::test(start_paused = true)]
+async fn reset_at() {
+    let start = Instant::now();
+
+    // This is necessary because the timer is only so granular, and in order for
+    // all our ticks to resolve, the time needs to be 1ms ahead of what we
+    // expect, so that the runtime will see that it is time to resolve the timer
+    time::advance(ms(1)).await;
+
+    let mut i = task::spawn(time::interval_at(start, ms(300)));
+
+    check_interval_poll!(i, start, 0);
+
+    time::advance(ms(100)).await;
+    check_interval_poll!(i, start);
+
+    time::advance(ms(200)).await;
+    check_interval_poll!(i, start, 300);
+
+    time::advance(ms(100)).await;
+    check_interval_poll!(i, start);
+
+    i.reset_at(Instant::now() + Duration::from_millis(40));
+
+    // We add one because when using `reset` method, `Interval` adds the
+    // `period` from `Instant::now()`, which will always be off by one
+    time::advance(ms(40)).await;
+    check_interval_poll!(i, start, 441);
+
+    time::advance(ms(100)).await;
+    check_interval_poll!(i, start);
+
+    time::advance(ms(200)).await;
+    check_interval_poll!(i, start, 741);
+}
+
 fn poll_next(interval: &mut task::Spawn<time::Interval>) -> Poll<Instant> {
     interval.enter(|cx, mut interval| interval.poll_tick(cx))
 }