LibWeb: Create list-item markers during layout tree construction

Previously, these were added during layout. This didn't fit into the new
world where layout doesn't mutate the tree incrementally, so this patch
adds logic to Layout::TreeBuilder for adding a marker to each list-item
box after its children have been constructed.

Userland/Libraries/LibWeb/Forward.h

@@ -291,6 +291,8 @@ class Label;
 class LabelableNode;
 class LineBox;
 class LineBoxFragment;
+class ListItemBox;
+class ListItemMarkerBox;
 class Node;
 class NodeWithStyle;
 class NodeWithStyleAndBoxModelMetrics;

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -405,10 +405,9 @@ void BlockFormattingContext::layout_block_level_children(BlockContainer const& b
         if (is<ReplacedBox>(child_box) || is<BlockContainer>(child_box))
             place_block_level_element_in_normal_flow_horizontally(child_box, block_container);
 
-        // FIXME: This should be factored differently. It's uncool that we mutate the tree *during* layout!
-        //        Instead, we should generate the marker box during the tree build.
-        if (is<ListItemBox>(child_box))
-            verify_cast<ListItemBox>(child_box).layout_marker();
+        if (is<ListItemBox>(child_box)) {
+            layout_list_item_marker(static_cast<ListItemBox const&>(child_box));
+        }
 
         content_height = max(content_height, box_state.offset.y() + box_state.content_height + box_state.margin_box_bottom());
         content_width = max(content_width, box_state.content_width);
@@ -663,4 +662,36 @@ void BlockFormattingContext::layout_floating_child(Box const& box, BlockContaine
         float_box(FloatSide::Right, m_right_floats);
     }
 }
+
+void BlockFormattingContext::layout_list_item_marker(ListItemBox const& list_item_box)
+{
+    if (!list_item_box.marker())
+        return;
+
+    auto& marker = *list_item_box.marker();
+    auto& marker_state = m_state.ensure(marker);
+    auto& list_item_state = m_state.ensure(list_item_box);
+
+    int image_width = 0;
+    int image_height = 0;
+    if (auto const* list_style_image = marker.list_style_image_bitmap()) {
+        image_width = list_style_image->rect().width();
+        image_height = list_style_image->rect().height();
+    }
+
+    if (marker.text().is_empty()) {
+        marker_state.content_width = image_width + 4;
+    } else {
+        auto text_width = marker.font().width(marker.text());
+        marker_state.content_width = image_width + text_width;
+    }
+
+    marker_state.content_height = max(image_height, marker.line_height());
+
+    marker_state.offset = { -(marker_state.content_width + 4), 0 };
+
+    if (marker_state.content_height > list_item_state.content_height)
+        list_item_state.content_height = marker_state.content_height;
+}
+
 }

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2020-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -58,6 +58,8 @@ private:
 
     void apply_transformations_to_children(Box const&);
 
+    void layout_list_item_marker(ListItemBox const&);
+
     enum class FloatSide {
         Left,
         Right,

Userland/Libraries/LibWeb/Layout/ListItemBox.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -19,30 +19,9 @@ ListItemBox::~ListItemBox()
 {
 }
 
-void ListItemBox::layout_marker()
+void ListItemBox::set_marker(RefPtr<ListItemMarkerBox> marker)
 {
-    if (m_marker) {
-        remove_child(*m_marker);
-        m_marker = nullptr;
-    }
-
-    if (computed_values().list_style_type() == CSS::ListStyleType::None)
-        return;
-
-    if (!m_marker) {
-        auto* marker_style = dom_node().specified_css_values();
-        VERIFY(marker_style);
-        int child_index = parent()->index_of_child<ListItemBox>(*this).value();
-        m_marker = adopt_ref(*new ListItemMarkerBox(document(), computed_values().list_style_type(), child_index + 1, *marker_style));
-        if (first_child())
-            m_marker->set_inline(first_child()->is_inline());
-        append_child(*m_marker);
-    }
-
-    m_marker->set_offset(-(m_marker->content_width() + 4), 0);
-
-    if (m_marker->content_height() > content_height())
-        set_content_height(m_marker->content_height());
+    m_marker = move(marker);
 }
 
 }

Userland/Libraries/LibWeb/Layout/ListItemBox.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -11,18 +11,17 @@
 
 namespace Web::Layout {
 
-class ListItemMarkerBox;
-
 class ListItemBox final : public BlockContainer {
 public:
     ListItemBox(DOM::Document&, DOM::Element&, NonnullRefPtr<CSS::StyleProperties>);
     virtual ~ListItemBox() override;
 
-    void layout_marker();
-
     DOM::Element& dom_node() { return static_cast<DOM::Element&>(*BlockContainer::dom_node()); }
     DOM::Element const& dom_node() const { return static_cast<DOM::Element const&>(*BlockContainer::dom_node()); }
 
+    ListItemMarkerBox const* marker() const { return m_marker; }
+    void set_marker(RefPtr<ListItemMarkerBox>);
+
 private:
     RefPtr<ListItemMarkerBox> m_marker;
 };

Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -48,22 +48,6 @@ ListItemMarkerBox::ListItemMarkerBox(DOM::Document& document, CSS::ListStyleType
     default:
         VERIFY_NOT_REACHED();
     }
-
-    int image_width = 0;
-    int image_height = 0;
-    if (auto const* list_style_image = list_style_image_bitmap()) {
-        image_width = list_style_image->rect().width();
-        image_height = list_style_image->rect().height();
-    }
-
-    if (m_text.is_null()) {
-        set_content_width(image_width + 4);
-    } else {
-        auto text_width = font().width(m_text);
-        set_content_width(image_width + text_width);
-    }
-
-    set_content_height(max(image_height, line_height()));
 }
 
 ListItemMarkerBox::~ListItemMarkerBox()

Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  * Copyright (c) 2021, Tobias Christiansen <tobyase@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
@@ -18,9 +18,11 @@ public:
 
     virtual void paint(PaintContext&, PaintPhase) override;
 
+    Gfx::Bitmap const* list_style_image_bitmap() const;
+    String const& text() const { return m_text; }
+
 private:
     virtual bool can_have_children() const override { return false; }
-    Gfx::Bitmap const* list_style_image_bitmap() const;
 
     CSS::ListStyleType m_list_style_type { CSS::ListStyleType::None };
     size_t m_index;

Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2021, Andreas Kling <kling@serenityos.org>
+ * Copyright (c) 2018-2022, Andreas Kling <kling@serenityos.org>
  *
  * SPDX-License-Identifier: BSD-2-Clause
  */
@@ -12,6 +12,8 @@
 #include <LibWeb/DOM/ShadowRoot.h>
 #include <LibWeb/Dump.h>
 #include <LibWeb/Layout/InitialContainingBlock.h>
+#include <LibWeb/Layout/ListItemBox.h>
+#include <LibWeb/Layout/ListItemMarkerBox.h>
 #include <LibWeb/Layout/Node.h>
 #include <LibWeb/Layout/TableBox.h>
 #include <LibWeb/Layout/TableCellBox.h>
@@ -147,6 +149,16 @@ void TreeBuilder::create_layout_tree(DOM::Node& dom_node, TreeBuilder::Context&
         });
         pop_parent();
     }
+
+    if (is<ListItemBox>(*layout_node)) {
+        int child_index = layout_node->parent()->index_of_child<ListItemBox>(*layout_node).value();
+        auto marker_style = static_cast<DOM::Element const&>(dom_node).specified_css_values();
+        auto list_item_marker = adopt_ref(*new ListItemMarkerBox(document, layout_node->computed_values().list_style_type(), child_index + 1, *marker_style));
+        if (layout_node->first_child())
+            list_item_marker->set_inline(layout_node->first_child()->is_inline());
+        static_cast<ListItemBox&>(*layout_node).set_marker(list_item_marker);
+        layout_node->append_child(move(list_item_marker));
+    }
 }
 
 RefPtr<Node> TreeBuilder::build(DOM::Node& dom_node)