Fix issue where previous PositionInfo uses unset window index

When receiving a PlaybackInfo update from the internal player
with a discontinuity, while ExoPlayerImpl has an empty timeline,
we currently use C.INDEX_UNSET as the placeholder window index,
which is not valid.

In addition, receiving these stale discontinuities while both
the current and new timelines are empty are misleading anyway, so
added a new check to avoid sending out these specifcally. The
fix to pass in the current masking window index is still needed
to be absolutely sure it's set in case there is a discontinuity
at the same time as a change from an empty Timeline to a
non-empty one (wasn't able to craft a test for this case).

PiperOrigin-RevId: 831406115
(cherry picked from commit 9be90e0)

Author: tonihei

libraries/exoplayer/src/main/java/androidx/media3/exoplayer/ExoPlayerImpl.java

@@ -2158,12 +2158,17 @@ private void handlePlaybackInfo(ExoPlayerImplInternal.PlaybackInfoUpdate playbac
       }
       boolean positionDiscontinuity = false;
       long discontinuityWindowStartPositionUs = C.TIME_UNSET;
+      int oldMaskingMediaItemIndex = C.INDEX_UNSET;
       if (pendingDiscontinuity) {
-        positionDiscontinuity =
-            !playbackInfoUpdate.playbackInfo.periodId.equals(playbackInfo.periodId)
-                || playbackInfoUpdate.playbackInfo.discontinuityStartPositionUs
-                    != playbackInfo.positionUs;
+        boolean oldAndNewTimelineEmpty =
+            playbackInfoUpdate.playbackInfo.timeline.isEmpty() && playbackInfo.timeline.isEmpty();
+        boolean sameMediaPeriodId =
+            playbackInfoUpdate.playbackInfo.periodId.equals(playbackInfo.periodId);
+        boolean samePositon =
+            playbackInfoUpdate.playbackInfo.discontinuityStartPositionUs == playbackInfo.positionUs;
+        positionDiscontinuity = !oldAndNewTimelineEmpty && (!sameMediaPeriodId || !samePositon);
         if (positionDiscontinuity) {
+          oldMaskingMediaItemIndex = getCurrentMediaItemIndex();
           discontinuityWindowStartPositionUs =
               newTimeline.isEmpty() || playbackInfoUpdate.playbackInfo.periodId.isAd()
                   ? playbackInfoUpdate.playbackInfo.discontinuityStartPositionUs
@@ -2180,7 +2185,7 @@ private void handlePlaybackInfo(ExoPlayerImplInternal.PlaybackInfoUpdate playbac
           positionDiscontinuity,
           pendingDiscontinuityReason,
           discontinuityWindowStartPositionUs,
-          /* ignored */ C.INDEX_UNSET,
+          oldMaskingMediaItemIndex,
           /* repeatCurrentMediaItem= */ false);
     }
   }

libraries/exoplayer/src/test/java/androidx/media3/exoplayer/ExoPlayerTest.java

@@ -16535,6 +16535,50 @@ public void setAudioOutputProvider_forwardsProviderToAudioSink() throws Exceptio
     player.release();
   }
 
+  @Test
+  public void positionDiscontinuityFromInternalPlayer_whilePlaylistAlreadyCleared_isNotReported()
+      throws Exception {
+    FakeTimeline timeline = new FakeTimeline(/* windowCount= */ 1);
+    FakeMediaSource mediaSource =
+        new FakeMediaSource(timeline, ExoPlayerTestRunner.VIDEO_FORMAT) {
+          @Override
+          protected MediaPeriod createMediaPeriod(
+              MediaPeriodId id,
+              TrackGroupArray trackGroupArray,
+              Allocator allocator,
+              MediaSourceEventListener.EventDispatcher mediaSourceEventDispatcher,
+              DrmSessionManager drmSessionManager,
+              DrmSessionEventListener.EventDispatcher drmEventDispatcher,
+              @Nullable TransferListener transferListener) {
+            FakeMediaPeriod mediaPeriod =
+                new FakeMediaPeriod(
+                    trackGroupArray,
+                    allocator,
+                    TimelineWindowDefinition.DEFAULT_WINDOW_OFFSET_IN_FIRST_PERIOD_US,
+                    mediaSourceEventDispatcher,
+                    drmSessionManager,
+                    drmEventDispatcher,
+                    /* deferOnPrepared= */ false);
+            mediaPeriod.setSeekToUsOffset(10);
+            return mediaPeriod;
+          }
+        };
+    ExoPlayer player = parameterizeTestExoPlayerBuilder(new TestExoPlayerBuilder(context)).build();
+    Player.Listener listener = mock(Player.Listener.class);
+    player.addListener(listener);
+    player.setMediaSource(mediaSource);
+    player.prepare();
+    advance(player).untilState(Player.STATE_READY);
+
+    player.seekTo(10);
+    player.clearMediaItems();
+    advance(player).untilPendingCommandsAreFullyHandled();
+    player.release();
+
+    verify(listener, never())
+        .onPositionDiscontinuity(any(), any(), eq(DISCONTINUITY_REASON_SEEK_ADJUSTMENT));
+  }
+
   // Internal methods.
 
   private void addWatchAsSystemFeature() {