layout: Add %-unit-support to UnresolvedValue

Whatever % is resolved relative to still has to be added to the
properties we want it to work for.

layout/layout_box.cpp

@@ -146,8 +146,11 @@ std::string to_string(LayoutBox const &box) {
     return std::move(ss).str();
 }
 
-// NOLINTNEXTLINE(bugprone-easily-swappable-parameters)
-int to_px(std::string_view property, int const font_size, int const root_font_size) {
+// NOLINTBEGIN(bugprone-easily-swappable-parameters)
+int to_px(std::string_view property,
+        int const font_size,
+        int const root_font_size,
+        std::optional<int> parent_property_value) {
     // Special case for 0 since it won't ever have a unit that needs to be handled.
     if (property == "0") {
         return 0;
@@ -163,6 +166,15 @@ int to_px(std::string_view property, int const font_size, int const root_font_si
     auto const parsed_length = std::distance(property.data(), parse_result.ptr);
     auto const unit = property.substr(parsed_length);
 
+    if (unit == "%") {
+        if (!parent_property_value.has_value()) {
+            spdlog::warn("Missing parent-value for property w/ '%' unit");
+            return 0;
+        }
+
+        return static_cast<int>(res / 100.f * (*parent_property_value));
+    }
+
     if (unit == "px") {
         return static_cast<int>(res);
     }
@@ -180,5 +192,6 @@ int to_px(std::string_view property, int const font_size, int const root_font_si
     spdlog::warn("Bad property '{}' w/ unit '{}' in to_px", property, unit);
     return static_cast<int>(res);
 }
+// NOLINTEND(bugprone-easily-swappable-parameters)
 
 } // namespace layout

layout/layout_box.h

@@ -102,7 +102,10 @@ inline std::vector<LayoutBox const *> dom_children(LayoutBox const &node) {
 
 // TODO(robinlinden): This should be internal.
 // NOLINTNEXTLINE(bugprone-easily-swappable-parameters)
-int to_px(std::string_view property, int const font_size, int const root_font_size);
+int to_px(std::string_view property,
+        int const font_size,
+        int const root_font_size,
+        std::optional<int> parent_property_value = std::nullopt);
 
 } // namespace layout
 

layout/unresolved_value.cpp

@@ -8,7 +8,7 @@
 
 namespace layout {
 // NOLINTNEXTLINE(bugprone-easily-swappable-parameters)
-int UnresolvedValue::resolve(int font_size, int root_font_size) const {
-    return to_px(raw, font_size, root_font_size);
+int UnresolvedValue::resolve(int font_size, int root_font_size, std::optional<int> percent_relative_to) const {
+    return to_px(raw, font_size, root_font_size, percent_relative_to);
 }
 } // namespace layout

layout/unresolved_value.h

@@ -5,6 +5,7 @@
 #ifndef LAYOUT_UNRESOLVED_VALUE_H_
 #define LAYOUT_UNRESOLVED_VALUE_H_
 
+#include <optional>
 #include <string_view>
 
 namespace layout {
@@ -14,7 +15,7 @@ struct UnresolvedValue {
     [[nodiscard]] bool operator==(UnresolvedValue const &) const = default;
 
     constexpr bool is_auto() const { return raw == "auto"; }
-    int resolve(int font_size, int root_font_size) const;
+    int resolve(int font_size, int root_font_size, std::optional<int> percent_relative_to = std::nullopt) const;
 };
 
 } // namespace layout

layout/unresolved_value_test.cpp

@@ -33,5 +33,17 @@ int main() {
         a.expect_eq(uv.resolve(0, 0), 0);
     });
 
+    s.add_test("unit/%", [](etest::IActions &a) {
+        // Based on the third argument, whatever the spec wants the property
+        // this came from to be resolved against.
+        auto const uv = layout::UnresolvedValue{.raw = "50%"};
+        a.expect_eq(uv.resolve(100, 100, 100), 50);
+        a.expect_eq(uv.resolve(100, 100, 200), 100);
+        a.expect_eq(uv.resolve(0, 0, 1000), 500);
+
+        // If the third argument is not provided, you get nothing.
+        a.expect_eq(uv.resolve(123, 456), 0);
+    });
+
     return s.run();
 }