LibWeb: Avoid many style invalidations on DOM attribute mutation

Many times, attribute mutation doesn't necessitate a full style
invalidation on the element. However, the conditions are pretty
elaborate, so this first version has a lot of false positives.

We only need to invalidate style when any of these things apply:

1. The change may affect the match state of a selector somewhere.
2. The change may affect presentational hints applied to the element.

For (1) in this first version, we have a fixed list of attribute names
that may affect selectors. We also collect all names referenced by
attribute selectors anywhere in the document.

For (2), we add a new Element::is_presentational_hint() virtual that
tells us whether a given attribute name is a presentational hint.

This drastically reduces style work on many websites. As an example,
https://cnn.com/ is once again browseable.

Libraries/LibWeb/SVG/SVGCircleElement.cpp

@@ -29,6 +29,17 @@ void SVGCircleElement::initialize(JS::Realm& realm)
     WEB_SET_PROTOTYPE_FOR_INTERFACE(SVGCircleElement);
 }
 
+bool SVGCircleElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    return first_is_one_of(name,
+        SVG::AttributeNames::cx,
+        SVG::AttributeNames::cy,
+        SVG::AttributeNames::r);
+}
+
 void SVGCircleElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
     Base::apply_presentational_hints(cascaded_properties);

Libraries/LibWeb/SVG/SVGCircleElement.h

@@ -18,6 +18,7 @@ class SVGCircleElement final : public SVGGeometryElement {
 public:
     virtual ~SVGCircleElement() override = default;
 
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     virtual Gfx::Path get_path(CSSPixelSize viewport_size) override;

Libraries/LibWeb/SVG/SVGForeignObjectElement.cpp

@@ -52,6 +52,16 @@ GC::Ptr<Layout::Node> SVGForeignObjectElement::create_layout_node(GC::Ref<CSS::C
     return heap().allocate<Layout::SVGForeignObjectBox>(document(), *this, move(style));
 }
 
+bool SVGForeignObjectElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    return first_is_one_of(name,
+        SVG::AttributeNames::width,
+        SVG::AttributeNames::height);
+}
+
 void SVGForeignObjectElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
     Base::apply_presentational_hints(cascaded_properties);

Libraries/LibWeb/SVG/SVGForeignObjectElement.h

@@ -31,6 +31,7 @@ private:
     virtual void initialize(JS::Realm&) override;
     virtual void visit_edges(Cell::Visitor&) override;
 
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     GC::Ptr<SVG::SVGAnimatedLength> m_x;

Libraries/LibWeb/SVG/SVGGraphicsElement.cpp

@@ -143,32 +143,40 @@ struct NamedPropertyID {
     StringView name;
 };
 
+static Array const attribute_style_properties {
+    // FIXME: The `fill` attribute and CSS `fill` property are not the same! But our support is limited enough that they are equivalent for now.
+    NamedPropertyID(CSS::PropertyID::Fill),
+    // FIXME: The `stroke` attribute and CSS `stroke` property are not the same! But our support is limited enough that they are equivalent for now.
+    NamedPropertyID(CSS::PropertyID::Stroke),
+    NamedPropertyID(CSS::PropertyID::StrokeDasharray),
+    NamedPropertyID(CSS::PropertyID::StrokeDashoffset),
+    NamedPropertyID(CSS::PropertyID::StrokeLinecap),
+    NamedPropertyID(CSS::PropertyID::StrokeLinejoin),
+    NamedPropertyID(CSS::PropertyID::StrokeMiterlimit),
+    NamedPropertyID(CSS::PropertyID::StrokeWidth),
+    NamedPropertyID(CSS::PropertyID::FillRule),
+    NamedPropertyID(CSS::PropertyID::FillOpacity),
+    NamedPropertyID(CSS::PropertyID::StrokeOpacity),
+    NamedPropertyID(CSS::PropertyID::Opacity),
+    NamedPropertyID(CSS::PropertyID::TextAnchor),
+    NamedPropertyID(CSS::PropertyID::FontSize),
+    NamedPropertyID(CSS::PropertyID::Mask),
+    NamedPropertyID(CSS::PropertyID::MaskType),
+    NamedPropertyID(CSS::PropertyID::ClipPath),
+    NamedPropertyID(CSS::PropertyID::ClipRule),
+    NamedPropertyID(CSS::PropertyID::Display),
+};
+
+bool SVGGraphicsElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    return any_of(attribute_style_properties, [&](auto& property) { return name.equals_ignoring_ascii_case(property.name); });
+}
+
 void SVGGraphicsElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
-    static Array const attribute_style_properties {
-        // FIXME: The `fill` attribute and CSS `fill` property are not the same! But our support is limited enough that they are equivalent for now.
-        NamedPropertyID(CSS::PropertyID::Fill),
-        // FIXME: The `stroke` attribute and CSS `stroke` property are not the same! But our support is limited enough that they are equivalent for now.
-        NamedPropertyID(CSS::PropertyID::Stroke),
-        NamedPropertyID(CSS::PropertyID::StrokeDasharray),
-        NamedPropertyID(CSS::PropertyID::StrokeDashoffset),
-        NamedPropertyID(CSS::PropertyID::StrokeLinecap),
-        NamedPropertyID(CSS::PropertyID::StrokeLinejoin),
-        NamedPropertyID(CSS::PropertyID::StrokeMiterlimit),
-        NamedPropertyID(CSS::PropertyID::StrokeWidth),
-        NamedPropertyID(CSS::PropertyID::FillRule),
-        NamedPropertyID(CSS::PropertyID::FillOpacity),
-        NamedPropertyID(CSS::PropertyID::StrokeOpacity),
-        NamedPropertyID(CSS::PropertyID::Opacity),
-        NamedPropertyID(CSS::PropertyID::TextAnchor),
-        NamedPropertyID(CSS::PropertyID::FontSize),
-        NamedPropertyID(CSS::PropertyID::Mask),
-        NamedPropertyID(CSS::PropertyID::MaskType),
-        NamedPropertyID(CSS::PropertyID::ClipPath),
-        NamedPropertyID(CSS::PropertyID::ClipRule),
-        NamedPropertyID(CSS::PropertyID::Display),
-    };
-
     CSS::Parser::ParsingContext parsing_context { document(), CSS::Parser::ParsingContext::Mode::SVGPresentationAttribute };
     for_each_attribute([&](auto& name, auto& value) {
         for (auto property : attribute_style_properties) {

Libraries/LibWeb/SVG/SVGGraphicsElement.h

@@ -29,6 +29,7 @@ class SVGGraphicsElement : public SVGElement {
     WEB_PLATFORM_OBJECT(SVGGraphicsElement, SVGElement);
 
 public:
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     virtual void attribute_changed(FlyString const& name, Optional<String> const& old_value, Optional<String> const& value, Optional<FlyString> const& namespace_) override;

Libraries/LibWeb/SVG/SVGSVGElement.cpp

@@ -79,6 +79,20 @@ RefPtr<CSS::CSSStyleValue> SVGSVGElement::height_style_value_from_attribute() co
     return nullptr;
 }
 
+bool SVGSVGElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    return first_is_one_of(name,
+        SVG::AttributeNames::x,
+        SVG::AttributeNames::y,
+        SVG::AttributeNames::width,
+        SVG::AttributeNames::height,
+        SVG::AttributeNames::viewBox,
+        SVG::AttributeNames::preserveAspectRatio);
+}
+
 void SVGSVGElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
     Base::apply_presentational_hints(cascaded_properties);

Libraries/LibWeb/SVG/SVGSVGElement.h

@@ -31,6 +31,7 @@ class SVGSVGElement final : public SVGGraphicsElement
 public:
     virtual GC::Ptr<Layout::Node> create_layout_node(GC::Ref<CSS::ComputedProperties>) override;
 
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     virtual bool requires_svg_container() const override { return false; }

Libraries/LibWeb/SVG/SVGStopElement.cpp

@@ -30,6 +30,16 @@ void SVGStopElement::attribute_changed(FlyString const& name, Optional<String> c
     }
 }
 
+bool SVGStopElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    return first_is_one_of(name,
+        "stop-color"sv,
+        "stop-opacity"sv);
+}
+
 void SVGStopElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
     CSS::Parser::ParsingContext parsing_context { document() };

Libraries/LibWeb/SVG/SVGStopElement.h

@@ -25,6 +25,7 @@ public:
 
     GC::Ref<SVGAnimatedNumber> offset() const;
 
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     NumberPercentage stop_offset() const { return m_offset.value_or(NumberPercentage::create_number(0)); }

Libraries/LibWeb/SVG/SVGSymbolElement.cpp

@@ -39,11 +39,24 @@ void SVGSymbolElement::visit_edges(Cell::Visitor& visitor)
     visitor.visit(m_view_box_for_bindings);
 }
 
+bool SVGSymbolElement::is_presentational_hint(FlyString const& name) const
+{
+    if (Base::is_presentational_hint(name))
+        return true;
+
+    // FIXME: This is not a correct use of the presentational hint mechanism.
+    if (is_direct_child_of_use_shadow_tree())
+        return true;
+
+    return false;
+}
+
 // https://svgwg.org/svg2-draft/struct.html#SymbolNotes
 void SVGSymbolElement::apply_presentational_hints(GC::Ref<CSS::CascadedProperties> cascaded_properties) const
 {
     Base::apply_presentational_hints(cascaded_properties);
 
+    // FIXME: This is not a correct use of the presentational hint mechanism.
     if (is_direct_child_of_use_shadow_tree()) {
         // The generated instance of a ‘symbol’ that is the direct referenced element of a ‘use’ element must always have a computed value of inline for the display property.
         cascaded_properties->set_property_from_presentational_hint(CSS::PropertyID::Display, CSS::DisplayStyleValue::create(CSS::Display::from_short(CSS::Display::Short::Inline)));

Libraries/LibWeb/SVG/SVGSymbolElement.h

@@ -19,6 +19,7 @@ class SVGSymbolElement final : public SVGGraphicsElement
 public:
     virtual ~SVGSymbolElement() override = default;
 
+    virtual bool is_presentational_hint(FlyString const&) const override;
     virtual void apply_presentational_hints(GC::Ref<CSS::CascadedProperties>) const override;
 
     virtual Optional<ViewBox> view_box() const override { return m_view_box; }