Support parsing <shadow> (#48991)

Summary:

This adds support for parsing the `<shadow>` data type. In combination with `CSSCommaSeparatedList`, we can now parse box shadow expressions.

Reviewed By: lenaic

Differential Revision: D68744811

Author: NickGerleman

packages/react-native/ReactCommon/react/renderer/css/CSSShadow.h

@@ -0,0 +1,145 @@
+/*
+ * Copyright (c) Meta Platforms, Inc. and affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+#pragma once
+
+#include <optional>
+#include <tuple>
+
+#include <react/renderer/css/CSSColor.h>
+#include <react/renderer/css/CSSDataType.h>
+#include <react/renderer/css/CSSKeyword.h>
+#include <react/renderer/css/CSSLength.h>
+#include <react/renderer/css/CSSValueParser.h>
+#include <react/utils/to_underlying.h>
+
+namespace facebook::react {
+
+/**
+ * Representation of CSS <shadow> data type
+ * https://drafts.csswg.org/css-backgrounds/#typedef-shadow
+ */
+struct CSSShadow {
+  CSSLength offsetX{};
+  CSSLength offsetY{};
+  CSSLength blurRadius{};
+  CSSLength spreadDistance{};
+  CSSColor color{CSSColor::black()};
+  bool inset{false};
+
+  constexpr bool operator==(const CSSShadow& rhs) const = default;
+};
+
+/**
+ * Represents a keyword for an inset shadow.
+ */
+enum class CSSInsetShadowKeyword : std::underlying_type_t<CSSKeyword> {
+  Inset = to_underlying(CSSKeyword::Inset),
+};
+
+static_assert(CSSDataType<CSSInsetShadowKeyword>);
+
+template <>
+struct CSSDataTypeParser<CSSShadow> {
+  static constexpr auto consume(CSSSyntaxParser& parser)
+      -> std::optional<CSSShadow> {
+    std::optional<CSSColor> color{};
+    bool inset{false};
+    std::optional<std::tuple<CSSLength, CSSLength, CSSLength, CSSLength>>
+        lengths{};
+
+    for (auto nextValue =
+             parseNextCSSValue<CSSLength, CSSColor, CSSInsetShadowKeyword>(
+                 parser);
+         !std::holds_alternative<std::monostate>(nextValue);
+         nextValue =
+             parseNextCSSValue<CSSLength, CSSColor, CSSInsetShadowKeyword>(
+                 parser, CSSDelimiter::Whitespace)) {
+      if (std::holds_alternative<CSSLength>(nextValue)) {
+        if (lengths.has_value()) {
+          return {};
+        }
+        lengths = parseRestLengths(std::get<CSSLength>(nextValue), parser);
+        if (!lengths.has_value()) {
+          return {};
+        }
+        continue;
+      }
+
+      if (std::holds_alternative<CSSColor>(nextValue)) {
+        if (color.has_value()) {
+          return {};
+        }
+        color = std::get<CSSColor>(nextValue);
+        continue;
+      }
+
+      if (std::holds_alternative<CSSInsetShadowKeyword>(nextValue)) {
+        if (inset) {
+          return {};
+        }
+        inset = true;
+        continue;
+      }
+    }
+
+    if (!lengths.has_value()) {
+      return {};
+    }
+
+    return CSSShadow{
+        .offsetX = std::get<0>(*lengths),
+        .offsetY = std::get<1>(*lengths),
+        .blurRadius = std::get<2>(*lengths),
+        .spreadDistance = std::get<3>(*lengths),
+        .color = color.value_or(CSSColor::black()),
+        .inset = inset,
+    };
+  }
+
+ private:
+  static constexpr auto parseRestLengths(
+      CSSLength offsetX,
+      CSSSyntaxParser& parser)
+      -> std::optional<std::tuple<CSSLength, CSSLength, CSSLength, CSSLength>> {
+    auto offsetY =
+        parseNextCSSValue<CSSLength>(parser, CSSDelimiter::Whitespace);
+    if (std::holds_alternative<std::monostate>(offsetY)) {
+      return {};
+    }
+
+    auto blurRadius =
+        parseNextCSSValue<CSSLength>(parser, CSSDelimiter::Whitespace);
+    if (std::holds_alternative<std::monostate>(blurRadius)) {
+      return std::make_tuple(
+          offsetX, std::get<CSSLength>(offsetY), CSSLength{}, CSSLength{});
+    }
+    if (std::get<CSSLength>(blurRadius).value < 0) {
+      return {};
+    }
+
+    auto spreadDistance =
+        parseNextCSSValue<CSSLength>(parser, CSSDelimiter::Whitespace);
+    if (std::holds_alternative<std::monostate>(spreadDistance)) {
+      return std::make_tuple(
+          offsetX,
+          std::get<CSSLength>(offsetY),
+          std::get<CSSLength>(blurRadius),
+          CSSLength{});
+    }
+
+    return std::make_tuple(
+        offsetX,
+        std::get<CSSLength>(offsetY),
+        std::get<CSSLength>(blurRadius),
+        std::get<CSSLength>(spreadDistance));
+  }
+};
+
+static_assert(CSSDataType<CSSShadow>);
+
+} // namespace facebook::react