LibWeb: Retain display: contents in ancestor stack for continuations

When restructuring inline nodes because of a block element insertion
during the layout tree build, we might end up with a `display: contents`
element in the ancestor stack that is not part of the actual layout
tree, since it's never actually used as a parent for any node. Because
we were only rewinding the ancestor stack with actual new layout nodes,
it became corrupted and layout nodes were added to the wrong parent.

This new logic leaves the ancestor stack intact, only replacing layout
nodes whenever a new one is created.

Libraries/LibWeb/Layout/TreeBuilder.cpp

@@ -305,13 +305,11 @@ void TreeBuilder::restructure_block_node_in_inline_parent(NodeWithStyleAndBoxMod
     }();
     nearest_block_ancestor.set_children_are_inline(false);
 
-    // Unwind the ancestor stack to find the topmost inline ancestor.
+    // Find the topmost inline ancestor.
     GC::Ptr<NodeWithStyleAndBoxModelMetrics> topmost_inline_ancestor;
     for (auto* ancestor = &parent; ancestor; ancestor = ancestor->parent()) {
         if (ancestor == &nearest_block_ancestor)
             break;
-        if (ancestor == m_ancestor_stack.last())
-            m_ancestor_stack.take_last();
         if (ancestor->is_inline())
             topmost_inline_ancestor = static_cast<NodeWithStyleAndBoxModelMetrics*>(ancestor);
     }
@@ -320,7 +318,7 @@ void TreeBuilder::restructure_block_node_in_inline_parent(NodeWithStyleAndBoxMod
     // We need to host the topmost inline ancestor and its previous siblings in an anonymous "before" wrapper. If an
     // inline wrapper does not already exist, we create a new one and add it to the nearest block ancestor.
     GC::Ptr<Node> before_wrapper;
-    if (auto last_child = nearest_block_ancestor.last_child(); last_child->is_anonymous() && last_child->children_are_inline()) {
+    if (auto* last_child = nearest_block_ancestor.last_child(); last_child->is_anonymous() && last_child->children_are_inline()) {
         before_wrapper = last_child;
     } else {
         before_wrapper = nearest_block_ancestor.create_anonymous_wrapper();
@@ -388,21 +386,19 @@ void TreeBuilder::restructure_block_node_in_inline_parent(NodeWithStyleAndBoxMod
             current_parent->append_child(new_inline_node);
             current_parent = new_inline_node;
 
-            // Stop recreating nodes when we've reached node's parent
+            // Replace the node in the ancestor stack with the new node.
+            auto& node_with_style = static_cast<NodeWithStyle&>(*inline_node);
+            if (auto stack_index = m_ancestor_stack.find_first_index(node_with_style); stack_index.has_value())
+                m_ancestor_stack[stack_index.release_value()] = new_inline_node;
+
+            // Stop recreating nodes when we've reached node's parent.
             if (inline_node == &parent)
                 break;
         }
 
         after_wrapper->set_children_are_inline(true);
         nearest_block_ancestor.append_child(after_wrapper);
     }
-
-    // Rewind the ancestor stack
-    for (GC::Ptr<Node> inline_node = topmost_inline_ancestor; inline_node; inline_node = inline_node->last_child()) {
-        if (!is<NodeWithStyle>(*inline_node))
-            break;
-        m_ancestor_stack.append(static_cast<NodeWithStyle&>(*inline_node));
-    }
 }
 
 static bool is_ignorable_whitespace(Layout::Node const& node)

Tests/LibWeb/Ref/expected/block-element-inside-inline-element-ref.html

@@ -18,5 +18,7 @@
     <b>foo</b><div><b>bar</b></div><b>baz</b>
     <hr>
     <span>foo</span><div>bar</div>
+    <hr>
+    <b>foo</b><div><b>bar</b></div><b>baz</b>
 </body>
 </html>

Tests/LibWeb/Ref/input/block-element-inside-inline-element.html

@@ -40,5 +40,8 @@
             target2.setAttribute('style', null);
         });
     </script>
+    <!-- Block inside `display: contents` element -->
+    <hr>
+    <b>foo<div style="display: contents"><div>bar</div></div>baz</b>
 </body>
 </html>