Bug 1825611: Trim bounds when hittesting overflow:hidden containers r=Jamie

Differential Revision: https://phabricator.services.mozilla.com/D175194

accessible/ipc/RemoteAccessibleBase.cpp

@@ -629,6 +629,17 @@ bool RemoteAccessibleBase<Derived>::IsFixedPos() const {
   return false;
 }
 
+template <class Derived>
+bool RemoteAccessibleBase<Derived>::IsOverflowHidden() const {
+  MOZ_ASSERT(mCachedFields);
+  if (auto maybeOverflow =
+          mCachedFields->GetAttribute<RefPtr<nsAtom>>(nsGkAtoms::overflow)) {
+    return *maybeOverflow == nsGkAtoms::hidden;
+  }
+
+  return false;
+}
+
 template <class Derived>
 LayoutDeviceIntRect RemoteAccessibleBase<Derived>::BoundsWithOffset(
     Maybe<nsRect> aOffset, bool aBoundsAreForHittesting) const {
@@ -705,11 +716,12 @@ LayoutDeviceIntRect RemoteAccessibleBase<Derived>::BoundsWithOffset(
           // that the bounds we've calculated so far are constrained to the
           // bounds of the scroll area. Without this, we'll "hit" the off-screen
           // portions of accs that are are partially (but not fully) within the
-          // scroll area.
-          if (aBoundsAreForHittesting && hasScrollArea) {
-            nsRect selfRelativeScrollBounds(0, 0, remoteBounds.width,
-                                            remoteBounds.height);
-            bounds = bounds.SafeIntersect(selfRelativeScrollBounds);
+          // scroll area. This is also a problem for accs with overflow:hidden;
+          if (aBoundsAreForHittesting &&
+              (hasScrollArea || remoteAcc->IsOverflowHidden())) {
+            nsRect selfRelativeVisibleBounds(0, 0, remoteBounds.width,
+                                             remoteBounds.height);
+            bounds = bounds.SafeIntersect(selfRelativeVisibleBounds);
           }
         }
         if (remoteAcc->IsDoc()) {

accessible/ipc/RemoteAccessibleBase.h

@@ -443,6 +443,7 @@ class RemoteAccessibleBase : public Accessible, public HyperTextAccessibleBase {
   LayoutDeviceIntRect BoundsWithOffset(
       Maybe<nsRect> aOffset, bool aBoundsAreForHittesting = false) const;
   bool IsFixedPos() const;
+  bool IsOverflowHidden() const;
 
   // This function is used exclusively for hit testing.
   bool ContainsPoint(int32_t aX, int32_t aY);