Bug 1740289 - Notify onShowDynamicToolbar on overflow: hidden case. r=geckoview-reviewers,agi,emilio

The reason why we don't change GetOverflowState is that GetOverflowState is also
used for overflow/underflow event firing and our frontend code expects both
the events are fired on overflow:hidden elements [1]. And it looks like it's by
design as per one of test cases for overflow events has `overflow:hidden` style
in the first place.

[1] https://searchfox.org/mozilla-central/rev/df6434d2ebfdf2b5f89f205fc81d60d64a774fe1/devtools/client/shared/components/tabs/Tabs.css#38-39
[2] https://searchfox.org/mozilla-central/rev/df6434d2ebfdf2b5f89f205fc81d60d64a774fe1/layout/generic/test/test_overflow_event.html#46

Differential Revision: https://phabricator.services.mozilla.com/D131103

layout/generic/nsGfxScrollFrame.cpp

@@ -2271,6 +2271,9 @@ ScrollFrameHelper::ScrollFrameHelper(nsContainerFrame* aOuter, bool aIsRoot)
       mApzAnimationRequested(false),
       mReclampVVOffsetInReflowFinished(false),
       mMayScheduleScrollAnimations(false),
+#ifdef MOZ_WIDGET_ANDROID
+      mHasVerticalOverflowForDynamicToolbar(false),
+#endif
       mVelocityQueue(aOuter->PresContext()) {
   AppendScrollUpdate(ScrollPositionUpdate::NewScrollframe(nsPoint()));
 
@@ -6447,9 +6450,14 @@ bool ScrollFrameHelper::ReflowFinished() {
     }
 
 #if defined(MOZ_WIDGET_ANDROID)
-    if (mIsRoot && !(GetOverflowState() & OverflowState::Vertical)) {
+    const bool hasVerticalOverflow =
+        GetOverflowState() & OverflowState::Vertical &&
+        GetScrollStylesFromFrame().mVertical != StyleOverflow::Hidden;
+    if (!mFirstReflow && mHasVerticalOverflowForDynamicToolbar &&
+        !hasVerticalOverflow) {
       mOuter->PresShell()->MaybeNotifyShowDynamicToolbar();
     }
+    mHasVerticalOverflowForDynamicToolbar = hasVerticalOverflow;
 #endif  // defined(MOZ_WIDGET_ANDROID)
   }
 

layout/generic/nsGfxScrollFrame.h

@@ -766,6 +766,11 @@ class ScrollFrameHelper : public nsIReflowCallback {
   // Whether we need to schedule the scroll-linked animations.
   bool mMayScheduleScrollAnimations : 1;
 
+#ifdef MOZ_WIDGET_ANDROID
+  // True if this scrollable frame was vertically overflowed on the last reflow.
+  bool mHasVerticalOverflowForDynamicToolbar : 1;
+#endif
+
   mozilla::layout::ScrollVelocityQueue mVelocityQueue;
 
  protected:

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

@@ -342,6 +342,34 @@ class DynamicToolbarTest : BaseSessionTest() {
             override fun onShowDynamicToolbar(session: GeckoSession) {
             }
         })
+    }
 
+    @WithDisplay(height = SCREEN_HEIGHT, width = SCREEN_WIDTH)
+    @Test fun showDynamicToolbarOnOverflowHidden() {
+        val dynamicToolbarMaxHeight = SCREEN_HEIGHT / 2
+        sessionRule.display?.run { setDynamicToolbarMaxHeight(dynamicToolbarMaxHeight) }
+
+        // Set active since setVerticalClipping call affects only for forground tab.
+        mainSession.setActive(true)
+
+        mainSession.loadTestPath(SHOW_DYNAMIC_TOOLBAR_HTML_PATH)
+        mainSession.waitForPageStop()
+        mainSession.evaluateJS("window.scrollTo(0, " + dynamicToolbarMaxHeight + ")")
+        mainSession.waitUntilCalled(object : ScrollDelegate {
+            @AssertCalled(count = 1)
+            override fun onScrollChanged(session: GeckoSession, scrollX: Int, scrollY: Int) {
+            }
+        })
+
+        // Simulate the dynamic toolbar being hidden by the scroll
+        sessionRule.display?.run { setVerticalClipping(-dynamicToolbarMaxHeight) }
+
+        mainSession.evaluateJS("document.documentElement.style.overflow = 'hidden'")
+
+        mainSession.waitUntilCalled(object : ContentDelegate {
+            @AssertCalled(count = 1)
+            override fun onShowDynamicToolbar(session: GeckoSession) {
+            }
+        })
     }
 }