LibWeb: Parse oblique font-style with an angle value

Author: https://github.com/tcl3
Commit: c0f9b11070
Pull-request: https://github.com/LadybirdBrowser/ladybird/pull/4552
Reviewed-by: https://github.com/konradekk

Libraries/LibWeb/CSS/StyleValues/FontStyleStyleValue.cpp

@@ -0,0 +1,42 @@
+/*
+ * Copyright (c) 2025, Tim Ledbetter <tim.ledbetter@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "FontStyleStyleValue.h"
+#include <LibWeb/CSS/CSSStyleValue.h>
+#include <LibWeb/CSS/Serialize.h>
+#include <LibWeb/CSS/StyleValues/AngleStyleValue.h>
+
+namespace Web::CSS {
+
+FontStyleStyleValue::FontStyleStyleValue(FontStyle font_style, ValueComparingRefPtr<CSSStyleValue const> angle_value)
+    : StyleValueWithDefaultOperators(Type::FontStyle)
+    , m_font_style(font_style)
+    , m_angle_value(angle_value)
+{
+}
+
+FontStyleStyleValue::~FontStyleStyleValue() = default;
+
+String FontStyleStyleValue::to_string(SerializationMode mode) const
+{
+    Optional<String> angle_string;
+    if (m_angle_value) {
+        angle_string = m_angle_value->to_string(mode);
+        if (m_font_style == FontStyle::Oblique && angle_string == "0deg"sv)
+            return "normal"_string;
+    }
+    StringBuilder builder;
+    builder.append(CSS::to_string(m_font_style));
+    // https://drafts.csswg.org/css-fonts/#valdef-font-style-oblique-angle--90deg-90deg
+    // The lack of an <angle> represents 14deg. (Note that a font might internally provide its own mapping for "oblique", but the mapping within the font is disregarded.)
+    static auto default_angle = Angle::make_degrees(14);
+    if (angle_string.has_value() && !(m_angle_value->is_angle() && m_angle_value->as_angle().angle() == default_angle))
+        builder.appendff(" {}", angle_string);
+
+    return MUST(builder.to_string());
+}
+
+}