LibWeb: Add layout objects for fieldset and legend

Add the boilerplate code for the layout objects that represent the
`<fieldset>` and `<legend>` elements. Using these, we can make progress
towards laying out these two elements per the spec at
https://html.spec.whatwg.org/multipage/rendering.html#the-fieldset-and-legend-elements.

Libraries/LibWeb/CMakeLists.txt

@@ -527,6 +527,7 @@ set(SOURCES
     Layout/BreakNode.cpp
     Layout/CanvasBox.cpp
     Layout/CheckBox.cpp
+    Layout/FieldSetBox.cpp
     Layout/FlexFormattingContext.cpp
     Layout/FormattingContext.cpp
     Layout/FrameBox.cpp
@@ -540,6 +541,7 @@ set(SOURCES
     Layout/Label.cpp
     Layout/LabelableNode.cpp
     Layout/LayoutState.cpp
+    Layout/LegendBox.cpp
     Layout/LineBox.cpp
     Layout/LineBoxFragment.cpp
     Layout/LineBuilder.cpp

Libraries/LibWeb/Forward.h

@@ -598,6 +598,7 @@ class BlockFormattingContext;
 class Box;
 class ButtonBox;
 class CheckBox;
+class FieldSetBox;
 class FlexFormattingContext;
 class FormattingContext;
 class ImageBox;
@@ -605,6 +606,7 @@ class InlineFormattingContext;
 class InlineNode;
 class Label;
 class LabelableNode;
+class LegendBox;
 class LineBox;
 class LineBoxFragment;
 class ListItemBox;

Libraries/LibWeb/HTML/HTMLFieldSetElement.cpp

@@ -14,6 +14,7 @@
 #include <LibWeb/HTML/HTMLOutputElement.h>
 #include <LibWeb/HTML/HTMLSelectElement.h>
 #include <LibWeb/HTML/HTMLTextAreaElement.h>
+#include <LibWeb/Layout/FieldSetBox.h>
 
 namespace Web::HTML {
 
@@ -77,4 +78,14 @@ GC::Ptr<DOM::HTMLCollection> const& HTMLFieldSetElement::elements()
     return m_elements;
 }
 
+Layout::FieldSetBox* HTMLFieldSetElement::layout_node()
+{
+    return static_cast<Layout::FieldSetBox*>(Node::layout_node());
+}
+
+JS::GCPtr<Layout::Node> HTMLFieldSetElement::create_layout_node(CSS::StyleProperties style)
+{
+    return heap().allocate<Layout::FieldSetBox>(document(), *this, style);
+}
+
 }

Libraries/LibWeb/HTML/HTMLFieldSetElement.h

@@ -42,6 +42,10 @@ public:
 
     virtual Optional<ARIA::Role> default_role() const override { return ARIA::Role::group; }
 
+    virtual JS::GCPtr<Layout::Node> create_layout_node(CSS::StyleProperties) override;
+    Layout::FieldSetBox* layout_node();
+    Layout::FieldSetBox const* layout_node() const;
+
 private:
     HTMLFieldSetElement(DOM::Document&, DOM::QualifiedName);
 

Libraries/LibWeb/HTML/HTMLLegendElement.cpp

@@ -8,6 +8,7 @@
 #include <LibWeb/Bindings/Intrinsics.h>
 #include <LibWeb/HTML/HTMLFieldSetElement.h>
 #include <LibWeb/HTML/HTMLLegendElement.h>
+#include <LibWeb/Layout/LegendBox.h>
 
 namespace Web::HTML {
 
@@ -39,4 +40,19 @@ HTMLFormElement* HTMLLegendElement::form()
     return nullptr;
 }
 
+JS::GCPtr<Layout::Node> HTMLLegendElement::create_layout_node(CSS::StyleProperties style)
+{
+    return heap().allocate<Layout::LegendBox>(document(), *this, move(style));
+}
+
+Layout::LegendBox* HTMLLegendElement::layout_node()
+{
+    return static_cast<Layout::LegendBox*>(Node::layout_node());
+}
+
+Layout::LegendBox const* HTMLLegendElement::layout_node() const
+{
+    return static_cast<Layout::LegendBox const*>(Node::layout_node());
+}
+
 }

Libraries/LibWeb/HTML/HTMLLegendElement.h

@@ -7,6 +7,7 @@
 #pragma once
 
 #include <LibWeb/HTML/HTMLElement.h>
+#include <LibWeb/Layout/LegendBox.h>
 
 namespace Web::HTML {
 
@@ -19,6 +20,10 @@ public:
 
     HTMLFormElement* form();
 
+    virtual JS::GCPtr<Layout::Node> create_layout_node(CSS::StyleProperties) override;
+    Layout::LegendBox* layout_node();
+    Layout::LegendBox const* layout_node() const;
+
 private:
     HTMLLegendElement(DOM::Document&, DOM::QualifiedName);
 

Libraries/LibWeb/Layout/FieldSetBox.cpp

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2024, Kostya Farber <kostya.farber@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Forward.h>
+#include <LibWeb/HTML/HTMLLegendElement.h>
+#include <LibWeb/Layout/FieldSetBox.h>
+
+namespace Web::Layout {
+
+JS_DEFINE_ALLOCATOR(FieldSetBox);
+
+FieldSetBox::FieldSetBox(DOM::Document& document, DOM::Element& element, CSS::StyleProperties style)
+    : BlockContainer(document, &element, move(style))
+{
+}
+
+FieldSetBox::~FieldSetBox() = default;
+
+bool FieldSetBox::has_rendered_legend() const
+{
+    // https://html.spec.whatwg.org/#rendered-legend
+    if (this->has_children() && this->first_child()->is_legend_box()) {
+        auto* first_child = this->first_child();
+        return first_child->computed_values().float_() == CSS::Float::None
+            && first_child->computed_values().position() != CSS::Positioning::Absolute
+            && first_child->computed_values().position() != CSS::Positioning::Fixed;
+    }
+    return false;
+}
+
+}

Libraries/LibWeb/Layout/FieldSetBox.h

@@ -0,0 +1,37 @@
+/*
+ * Copyright (c) 2024, Kostya Farber <kostya.farber@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Forward.h>
+#include <LibWeb/Layout/BlockContainer.h>
+namespace Web::Layout {
+
+class FieldSetBox final : public BlockContainer {
+    JS_CELL(FieldSetBox, BlockContainer);
+    JS_DECLARE_ALLOCATOR(FieldSetBox);
+
+public:
+    FieldSetBox(DOM::Document&, DOM::Element&, CSS::StyleProperties);
+    virtual ~FieldSetBox() override;
+
+    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()); }
+
+    void layout_legend() const;
+
+private:
+    bool has_rendered_legend() const;
+    virtual bool is_fieldset_box() const final
+    {
+        return true;
+    }
+};
+
+template<>
+inline bool Node::fast_is<FieldSetBox>() const { return is_fieldset_box(); }
+
+}

Libraries/LibWeb/Layout/FormattingContext.cpp

@@ -111,6 +111,12 @@ bool FormattingContext::creates_block_formatting_context(Box const& box)
 
     // FIXME: column-span: all should always create a new formatting context, even when the column-span: all element isn't contained by a multicol container (Spec change, Chrome bug).
 
+    // https://html.spec.whatwg.org/#the-fieldset-and-legend-elements
+    if (box.is_fieldset_box())
+        // The fieldset element, when it generates a CSS box, is expected to act as follows:
+        // The element is expected to establish a new block formatting context.
+        return true;
+
     return false;
 }
 

Libraries/LibWeb/Layout/LegendBox.cpp

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2024, Kostya Farber <kostya.farber@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/Layout/LegendBox.h>
+
+namespace Web::Layout {
+
+JS_DEFINE_ALLOCATOR(LegendBox);
+
+LegendBox::LegendBox(DOM::Document& document, DOM::Element& element, CSS::StyleProperties style)
+    : BlockContainer(document, &element, move(style))
+{
+}
+
+LegendBox::~LegendBox() = default;
+
+}

Libraries/LibWeb/Layout/LegendBox.h

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2024, Kostya Farber <kostya.farber@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <LibWeb/Layout/BlockContainer.h>
+
+namespace Web::Layout {
+
+class LegendBox final : public BlockContainer {
+    JS_CELL(LegendBox, BlockContainer);
+    JS_DECLARE_ALLOCATOR(LegendBox);
+
+public:
+    LegendBox(DOM::Document&, DOM::Element&, CSS::StyleProperties);
+    virtual ~LegendBox() override;
+
+    DOM::Element& dom_node() { return static_cast<DOM::Element&>(*Box::dom_node()); }
+    DOM::Element const& dom_node() const { return static_cast<DOM::Element const&>(*Box::dom_node()); }
+
+private:
+    virtual bool is_legend_box() const final
+    {
+        return true;
+    }
+};
+
+template<>
+inline bool Node::fast_is<LegendBox>() const { return is_legend_box(); }
+
+}

Libraries/LibWeb/Layout/Node.h

@@ -115,6 +115,8 @@ public:
     virtual bool is_replaced_box() const { return false; }
     virtual bool is_list_item_box() const { return false; }
     virtual bool is_list_item_marker_box() const { return false; }
+    virtual bool is_fieldset_box() const { return false; }
+    virtual bool is_legend_box() const { return false; }
     virtual bool is_table_wrapper() const { return false; }
     virtual bool is_node_with_style_and_box_model_metrics() const { return false; }