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.

8 files changed, 65 insertions, 54 deletions

diff --git a/Userland/Libraries/LibWeb/Forward.h b/Userland/Libraries/LibWeb/Forward.h
index 6f8628b709..99a6dc760e 100644
--- a/Userland/Libraries/LibWeb/Forward.h
+++ b/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;
diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
index 1105aaec00..a1040b4057 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
+++ b/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;
+}
+
 }
diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h
index ef8371969b..1b8f38f8ba 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.h
+++ b/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,
diff --git a/Userland/Libraries/LibWeb/Layout/ListItemBox.cpp b/Userland/Libraries/LibWeb/Layout/ListItemBox.cpp
index 590873a943..a830b46c1f 100644
--- a/Userland/Libraries/LibWeb/Layout/ListItemBox.cpp
+++ b/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);
 }
 
 }
diff --git a/Userland/Libraries/LibWeb/Layout/ListItemBox.h b/Userland/Libraries/LibWeb/Layout/ListItemBox.h
index 4181b25ec7..eb08aea4fb 100644
--- a/Userland/Libraries/LibWeb/Layout/ListItemBox.h
+++ b/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;
 };
diff --git a/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.cpp b/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.cpp
index e9f4bc8720..9525e90f4a 100644
--- a/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.cpp
+++ b/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()
diff --git a/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.h b/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.h
index 85e79ef869..0e2b3d4a2b 100644
--- a/Userland/Libraries/LibWeb/Layout/ListItemMarkerBox.h
+++ b/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;
diff --git a/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp b/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp
index d5ccbc8ece..aff5847572 100644
--- a/Userland/Libraries/LibWeb/Layout/TreeBuilder.cpp
+++ b/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)