Bug 1916897 - Get rid of ScrollDirection::eVertical from APZHandledResult::mOverscrollDirections if mayTriggerPullToRefresh is false. r=botond,geckoview-reviewers,owlish

Though I personally think this fix is subtle, I have no other good idea to
solve the issue. Once after we have a separate API for dynamic toolbar, we
could handle this bug case in a clearer way.

This change doesn't have a dedicated test since there have been two JUnit tests
hitting this bug conditions.

(If we had been running tests on browsers which support both dynamic toolbar
and pull-to-refresh, this bug might have been noticed earlier?)

Differential Revision: https://phabricator.services.mozilla.com/D221105

Author: hiikezoe

gfx/layers/apz/src/APZInputBridge.cpp

@@ -149,6 +149,18 @@ void APZHandledResult::UpdateForTouchEvent(
                                           ? APZHandledPlace::HandledByRoot
                                           : APZHandledPlace::Unhandled,
                                       rootApzc});
+      if (aHandledResult && aHandledResult->IsHandledByRoot() &&
+          !mayTriggerPullToRefresh) {
+        MOZ_ASSERT(
+            !(aTarget->ScrollableDirections() & SideBits::eBottom),
+            "If we allowed moving the dynamic toolbar for the sub scroll "
+            "container, the sub scroll container should NOT be scrollable to "
+            "bottom");
+
+        // In cases we didn't allow pull-to-refresh (!mayTriggerPullToRefresh),
+        // it means the root scroll container is NOT overscrollable at top.
+        aHandledResult->mOverscrollDirections -= ScrollDirection::eVertical;
+      }
     }
   }
 }

mobile/android/geckoview/src/androidTest/java/org/mozilla/geckoview/test/InputResultDetailTest.kt

@@ -282,13 +282,17 @@ class InputResultDetailTest : BaseSessionTest() {
 
         value = sessionRule.waitForResult(sendDownEvent(50f, 50f))
 
-        // Now the touch event should be handed to the root scroller.
+        // Now the touch event should be handed off to the root scroller.
         assertResultDetail(
             "handoff",
             value,
             PanZoomController.INPUT_RESULT_HANDLED,
             PanZoomController.SCROLLABLE_FLAG_BOTTOM,
-            (PanZoomController.OVERSCROLL_FLAG_HORIZONTAL or PanZoomController.OVERSCROLL_FLAG_VERTICAL),
+            // Although the root scroll container is in fact over-scrollable
+            // vertically, the child scroll container is scrollabe to top,
+            // thus pull-to-refresh should not be triggered, that's the reason
+            // why we don't receive OVERSCROLL_FLAG_VERTICAL here.
+            PanZoomController.OVERSCROLL_FLAG_HORIZONTAL,
         )
     }
 
@@ -363,7 +367,11 @@ class InputResultDetailTest : BaseSessionTest() {
                 value,
                 PanZoomController.INPUT_RESULT_HANDLED,
                 PanZoomController.SCROLLABLE_FLAG_BOTTOM,
-                (PanZoomController.OVERSCROLL_FLAG_HORIZONTAL or PanZoomController.OVERSCROLL_FLAG_VERTICAL),
+                // Although the root scroll container is in fact over-scrollable
+                // vertically, the child scroll container is scrollabe to top,
+                // thus pull-to-refresh should not be triggered, that's the reason
+                // why we don't receive OVERSCROLL_FLAG_VERTICAL here.
+                PanZoomController.OVERSCROLL_FLAG_HORIZONTAL,
             )
         }
     }