LibWeb: Make Node::root return a reference

The root of a node can never be null, as "the root of an object is
itself, if its parent is null, or else it is the root of its parent."

https://dom.spec.whatwg.org/#concept-tree-root

Userland/Libraries/LibWeb/DOM/EventDispatcher.cpp

@@ -35,15 +35,15 @@ static EventTarget* retarget(EventTarget* left, EventTarget* right)
             return left;
 
         auto* left_node = verify_cast<Node>(left);
-        auto* left_root = left_node->root();
+        auto& left_root = left_node->root();
         if (!is<ShadowRoot>(left_root))
             return left;
 
-        if (is<Node>(right) && left_root->is_shadow_including_inclusive_ancestor_of(verify_cast<Node>(*right)))
+        if (is<Node>(right) && left_root.is_shadow_including_inclusive_ancestor_of(verify_cast<Node>(*right)))
             return left;
 
-        auto* left_shadow_root = verify_cast<ShadowRoot>(left_root);
-        left = left_shadow_root->host();
+        auto& left_shadow_root = verify_cast<ShadowRoot>(left_root);
+        left = left_shadow_root.host();
     }
 }
 

Userland/Libraries/LibWeb/DOM/Node.cpp

@@ -157,25 +157,28 @@ String Node::child_text_content() const
     return builder.build();
 }
 
-Node* Node::root()
+// https://dom.spec.whatwg.org/#concept-tree-root
+Node& Node::root()
 {
     Node* root = this;
     while (root->parent())
         root = root->parent();
-    return root;
+    return *root;
 }
 
-Node* Node::shadow_including_root()
+// https://dom.spec.whatwg.org/#concept-shadow-including-root
+Node& Node::shadow_including_root()
 {
-    auto node_root = root();
+    auto& node_root = root();
     if (is<ShadowRoot>(node_root))
-        return verify_cast<ShadowRoot>(node_root)->host()->shadow_including_root();
+        return verify_cast<ShadowRoot>(node_root).host()->shadow_including_root();
     return node_root;
 }
 
+// https://dom.spec.whatwg.org/#connected
 bool Node::is_connected() const
 {
-    return shadow_including_root() && shadow_including_root()->is_document();
+    return shadow_including_root().is_document();
 }
 
 Element* Node::parent_element()
@@ -608,7 +611,7 @@ u16 Node::compare_document_position(RefPtr<Node> other)
     // FIXME: Once LibWeb supports attribute nodes fix to follow the specification.
     VERIFY(node1->type() != NodeType::ATTRIBUTE_NODE && node2->type() != NodeType::ATTRIBUTE_NODE);
 
-    if ((node1 == nullptr || node2 == nullptr) || (node1->root() != node2->root()))
+    if ((node1 == nullptr || node2 == nullptr) || (&node1->root() != &node2->root()))
         return DOCUMENT_POSITION_DISCONNECTED | DOCUMENT_POSITION_IMPLEMENTATION_SPECIFIC | (node1 > node2 ? DOCUMENT_POSITION_PRECEDING : DOCUMENT_POSITION_FOLLOWING);
 
     if (node1->is_ancestor_of(*node2))
@@ -626,7 +629,7 @@ u16 Node::compare_document_position(RefPtr<Node> other)
 // https://dom.spec.whatwg.org/#concept-tree-host-including-inclusive-ancestor
 bool Node::is_host_including_inclusive_ancestor_of(const Node& other) const
 {
-    return is_inclusive_ancestor_of(other) || (is<DocumentFragment>(other.root()) && verify_cast<DocumentFragment>(other.root())->host() && is_inclusive_ancestor_of(*verify_cast<DocumentFragment>(other.root())->host().ptr()));
+    return is_inclusive_ancestor_of(other) || (is<DocumentFragment>(other.root()) && verify_cast<DocumentFragment>(other.root()).host() && is_inclusive_ancestor_of(*verify_cast<DocumentFragment>(other.root()).host().ptr()));
 }
 
 // https://dom.spec.whatwg.org/#dom-node-ownerdocument
@@ -691,10 +694,10 @@ bool Node::is_shadow_including_descendant_of(Node const& other) const
     if (!is<ShadowRoot>(root()))
         return false;
 
-    auto shadow_root = verify_cast<ShadowRoot>(root());
+    auto& shadow_root = verify_cast<ShadowRoot>(root());
 
     // NOTE: While host is nullable because of inheriting from DocumentFragment, shadow roots always have a host.
-    return shadow_root->host()->is_shadow_including_inclusive_descendant_of(other);
+    return shadow_root.host()->is_shadow_including_inclusive_descendant_of(other);
 }
 
 // https://dom.spec.whatwg.org/#concept-shadow-including-inclusive-descendant

Userland/Libraries/LibWeb/DOM/Node.h

@@ -113,14 +113,14 @@ public:
 
     String child_text_content() const;
 
-    Node* root();
-    const Node* root() const
+    Node& root();
+    const Node& root() const
     {
         return const_cast<Node*>(this)->root();
     }
 
-    Node* shadow_including_root();
-    const Node* shadow_including_root() const
+    Node& shadow_including_root();
+    const Node& shadow_including_root() const
     {
         return const_cast<Node*>(this)->shadow_including_root();
     }

Userland/Libraries/LibWeb/DOM/ShadowRoot.cpp

@@ -16,11 +16,12 @@ ShadowRoot::ShadowRoot(Document& document, Element& host)
     set_host(host);
 }
 
+// https://dom.spec.whatwg.org/#ref-for-get-the-parent%E2%91%A6
 EventTarget* ShadowRoot::get_parent(const Event& event)
 {
     if (!event.composed()) {
         auto& events_first_invocation_target = verify_cast<Node>(*event.path().first().invocation_target);
-        if (events_first_invocation_target.root() == this)
+        if (&events_first_invocation_target.root() == this)
             return nullptr;
     }
 

Userland/Libraries/LibWeb/Layout/Node.cpp

@@ -72,7 +72,7 @@ bool Node::establishes_stacking_context() const
 {
     if (!has_style())
         return false;
-    if (dom_node() == document().root())
+    if (dom_node() == &document().root())
         return true;
     auto position = computed_values().position();
     if (position == CSS::Position::Absolute || position == CSS::Position::Relative || position == CSS::Position::Fixed || position == CSS::Position::Sticky)