1 files changed, 24 insertions, 0 deletions
diff --git a/dom/base/Selection.h b/dom/base/Selection.h
index 08563993ac..101bada49f 100644
--- a/dom/base/Selection.h
+++ b/dom/base/Selection.h
@@ -386,6 +386,30 @@ class Selection final : public nsSupportsWeakReference,
     return mStyledRanges.mRanges[0].mRange->Collapsed();
   }
 
+  // Returns whether both normal range and cross-shadow-boundary
+  // range are collapsed.
+  //
+  // If StaticPrefs::dom_shadowdom_selection_across_boundary_enabled is
+  // disabled, this method always returns result as nsRange::IsCollapsed.
+  bool AreNormalAndCrossShadowBoundaryRangesCollapsed() const {
+    if (!IsCollapsed()) {
+      return false;
+    }
+
+    size_t cnt = mStyledRanges.Length();
+    if (cnt == 0) {
+      return true;
+    }
+
+    AbstractRange* range = mStyledRanges.mRanges[0].mRange;
+    MOZ_ASSERT_IF(
+        range->MayCrossShadowBoundary(),
+        !range->AsDynamicRange()->CrossShadowBoundaryRangeCollapsed());
+    // Returns false if nsRange::mCrossBoundaryRange exists,
+    // true otherwise.
+    return !range->MayCrossShadowBoundary();
+  }
+
   // *JS() methods are mapped to Selection.*().
   // They may move focus only when the range represents normal selection.
   // These methods shouldn't be used by non-JS callers.