Do not panic on navigating across documents

components/script/dom/document.rs

@@ -560,7 +560,8 @@ impl Document {
 
         let new_dirty_root = element
             .upcast::<Node>()
-            .common_ancestor(dirty_root.upcast(), ShadowIncluding::Yes);
+            .common_ancestor(dirty_root.upcast(), ShadowIncluding::Yes)
+            .expect("Couldn't find common ancestor");
 
         let mut has_dirty_descendants = true;
         for ancestor in dirty_root
@@ -1515,10 +1516,12 @@ impl Document {
             FireMouseEventType::Enter | FireMouseEventType::Leave
         ));
 
-        let common_ancestor = related_target.as_ref().map_or_else(
-            || DomRoot::from_ref(&*event_target),
-            |related_target| event_target.common_ancestor(related_target, ShadowIncluding::No),
-        );
+        let common_ancestor = match related_target.as_ref() {
+            Some(related_target) => event_target
+                .common_ancestor(related_target, ShadowIncluding::No)
+                .unwrap_or_else(|| DomRoot::from_ref(&*event_target)),
+            None => DomRoot::from_ref(&*event_target),
+        };
 
         // We need to create a target chain in case the event target shares
         // its boundaries with its ancestors.

components/script/dom/node.rs

@@ -708,16 +708,16 @@ impl Node {
         &self,
         other: &Node,
         shadow_including: ShadowIncluding,
-    ) -> DomRoot<Node> {
+    ) -> Option<DomRoot<Node>> {
         for ancestor in self.inclusive_ancestors(shadow_including) {
             if other
                 .inclusive_ancestors(shadow_including)
                 .any(|node| node == ancestor)
             {
-                return ancestor;
+                return Some(ancestor);
             }
         }
-        unreachable!();
+        None
     }
 
     pub fn is_inclusive_ancestor_of(&self, parent: &Node) -> bool {

components/script/dom/range.rs

@@ -298,6 +298,7 @@ impl RangeMethods for Range {
     fn CommonAncestorContainer(&self) -> DomRoot<Node> {
         self.EndContainer()
             .common_ancestor(&self.StartContainer(), ShadowIncluding::No)
+            .expect("Couldn't find common ancestor container")
     }
 
     // https://dom.spec.whatwg.org/#dom-range-setstart