LibWeb: Plumb calculated StyleValues into CSS::Length

This is a bit hackish, but this way the existance of the calc()
becomes transparent to the user who just wants a Length and doesn't
care where it came from.

Userland/Libraries/LibWeb/CSS/Length.cpp

@@ -76,6 +76,8 @@ const char* Length::unit_name() const
         return "vmax";
     case Type::Vmin:
         return "vmin";
+    case Type::Calculated:
+        return "calculated";
     }
     VERIFY_NOT_REACHED();
 }

Userland/Libraries/LibWeb/CSS/Length.h

@@ -16,6 +16,7 @@ public:
     enum class Type {
         Undefined,
         Percentage,
+        Calculated,
         Auto,
         Cm,
         In,
@@ -54,6 +55,8 @@ public:
             return fallback_for_undefined;
         if (is_percentage())
             return make_px(raw_value() / 100.0f * reference_for_percent);
+        if (is_calculated())
+            return {};
         if (is_relative())
             return make_px(to_px(layout_node));
         return *this;
@@ -71,8 +74,9 @@ public:
 
     bool is_undefined_or_auto() const { return m_type == Type::Undefined || m_type == Type::Auto; }
     bool is_undefined() const { return m_type == Type::Undefined; }
-    bool is_percentage() const { return m_type == Type::Percentage; }
+    bool is_percentage() const { return m_type == Type::Percentage || m_type == Type::Calculated; }
     bool is_auto() const { return m_type == Type::Auto; }
+    bool is_calculated() const { return m_type == Type::Calculated; }
 
     bool is_absolute() const
     {
@@ -122,6 +126,7 @@ public:
             return m_value * ((1.0f / 40.0f) * centimeter_pixels); // 1Q = 1/40th of 1cm
         case Type::Undefined:
         case Type::Percentage:
+        case Type::Calculated:
         default:
             VERIFY_NOT_REACHED();
         }
@@ -144,6 +149,8 @@ public:
         return !(*this == other);
     }
 
+    void set_calculated_style(CalculatedStyleValue* value) { m_calculated_style = value; }
+
 private:
     float relative_length_to_px(const Layout::Node&) const;
 
@@ -151,6 +158,8 @@ private:
 
     Type m_type { Type::Undefined };
     float m_value { 0 };
+
+    CalculatedStyleValue* m_calculated_style { nullptr };
 };
 
 }

Userland/Libraries/LibWeb/CSS/StyleProperties.cpp

@@ -55,6 +55,13 @@ Length StyleProperties::length_or_fallback(CSS::PropertyID id, const Length& fal
     auto value = property(id);
     if (!value.has_value())
         return fallback;
+
+    if (value.value()->is_calculated()) {
+        Length length = Length(0, Length::Type::Calculated);
+        length.set_calculated_style(verify_cast<CalculatedStyleValue>(value.value().ptr()));
+        return length;
+    }
+
     return value.value()->to_length();
 }
 

Userland/Libraries/LibWeb/Forward.h

@@ -14,6 +14,7 @@ enum class Source;
 }
 
 namespace Web::CSS {
+class CalculatedStyleValue;
 class CSSRule;
 class CSSImportRule;
 class CSSStyleDeclaration;