[Pager] Make Pager able to scroll by flinging a nested scroll child

pager/src/main/java/com/google/accompanist/pager/Pager.kt

@@ -385,6 +385,7 @@ internal fun Pager(
         ConsumeFlingNestedScrollConnection(
             consumeHorizontal = !isVertical,
             consumeVertical = isVertical,
+            pagerState = state,
         )
     }
 
@@ -449,9 +450,11 @@ internal fun Pager(
     }
 }
 
+@OptIn(ExperimentalPagerApi::class)
 private class ConsumeFlingNestedScrollConnection(
     private val consumeHorizontal: Boolean,
     private val consumeVertical: Boolean,
+    private val pagerState: PagerState,
 ) : NestedScrollConnection {
     override fun onPostScroll(
         consumed: Offset,
@@ -465,9 +468,15 @@ private class ConsumeFlingNestedScrollConnection(
     }
 
     override suspend fun onPostFling(consumed: Velocity, available: Velocity): Velocity {
-        // We can consume all post fling velocity on the main-axis
-        // so that it doesn't propagate up to the Pager
-        return available.consume(consumeHorizontal, consumeVertical)
+        return if (pagerState.currentPageLayoutInfo?.offset != 0) {
+            // The Pager is already scrolling. This means that a nested scroll child was
+            // scrolled to end, and the Pager can use this fling
+            Velocity.Zero
+        } else {
+            // A nested scroll child is still scrolling. We can consume all post fling
+            // velocity on the main-axis so that it doesn't propagate up to the Pager
+            available.consume(consumeHorizontal, consumeVertical)
+        }
     }
 }
 

pager/src/main/java/com/google/accompanist/pager/PagerState.kt

@@ -92,7 +92,7 @@ class PagerState(
 
     internal var afterContentPadding = 0
 
-    private val currentPageLayoutInfo: LazyListItemInfo?
+    internal val currentPageLayoutInfo: LazyListItemInfo?
         get() = lazyListState.layoutInfo.visibleItemsInfo.lastOrNull {
             it.index == currentPage
         }

pager/src/sharedTest/kotlin/com/google/accompanist/pager/HorizontalPagerScrollingContentTest.kt

@@ -89,6 +89,17 @@ class HorizontalPagerScrollingContentTest {
         // Assert that we're still on page 0
         assertThat(pagerState.currentPage).isEqualTo(0)
         assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)
+
+        // Perform a scroll in the same direction again
+        rule.onNodeWithTag(TestTag)
+            .swipeAcrossCenterWithVelocity(velocityPerSec = 2_000.dp, distancePercentageX = -0.5f)
+
+        // Wait for the flings to end
+        rule.waitForIdle()
+
+        // Assert that we're now on page 1
+        assertThat(pagerState.currentPage).isEqualTo(1)
+        assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)
     }
 
     companion object {

pager/src/sharedTest/kotlin/com/google/accompanist/pager/VerticalPagerScrollingContentTest.kt

@@ -88,6 +88,17 @@ class VerticalPagerScrollingContentTest {
         // Assert that we're still on page 0
         assertThat(pagerState.currentPage).isEqualTo(0)
         assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)
+
+        // Perform a scroll in the same direction again
+        rule.onNodeWithTag(TestTag)
+            .swipeAcrossCenterWithVelocity(velocityPerSec = 2_000.dp, distancePercentageY = -0.5f)
+
+        // Wait for the flings to end
+        rule.waitForIdle()
+
+        // Assert that we're now on page 1
+        assertThat(pagerState.currentPage).isEqualTo(1)
+        assertThat(pagerState.currentPageOffset).isWithin(0.01f).of(0f)
     }
 
     companion object {