fix: css important semantics (#792)

- **fix(css): align !important semantics across cascade**
- **perf(css): speed up CSSStyleDeclaration union/merge**
- **perf(css): skip pseudo-element matching when unused**
- **refactor(css): make inline styles Dart-only**
- **perf(css): gate pseudo emissions by rule features**
- **test(css): update snapshot for relayout-align-to-stretch integration
test**
- **fix(bridge): stabilize style export traversal**
- **perf(bridge): treat kLocalStyleChange as element-only**


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Inline and sheet styles now support !important and explicit
sheet-style updates for correct cascade behavior.
* Better support for pseudo-element styles
(before/after/first-letter/first-line).

* **Bug Fixes**
* More accurate style merging and fallback between inline and stylesheet
rules; computed styles reflect priority changes.

* **Chores**
* Refactored style handling and improved style recalculation performance
(reduced traversal work, caching).

* **Tests**
* Added and updated unit/integration tests covering important semantics
and inline/sheet interactions.

<sub>✏️ Tip: You can customize this high-level summary in your review
settings.</sub>
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: andycall

bridge/bindings/qjs/converter_impl.h

@@ -35,6 +35,7 @@
 
 #include "core/css/computed_css_style_declaration.h"
 #include "core/css/legacy/legacy_computed_css_style_declaration.h"
+#include "foundation/utility/make_visitor.h"
 
 namespace webf {
 
@@ -637,56 +638,6 @@ struct Converter<IDLNullable<T, typename std::enable_if_t<std::is_base_of<Script
   }
 };
 
-template <>
-struct Converter<ElementStyle> {
-  using ImplType = ElementStyle;
-
-  static ElementStyle FromValue(JSContext* ctx, JSValue value, ExceptionState& exception_state) {
-    auto ectx = ExecutingContext::From(ctx);
-    if (ectx->isBlinkEnabled()) {
-      if (JS_IsNull(value)) {
-        return static_cast<InlineCssStyleDeclaration*>(nullptr);
-      }
-
-      return Converter<InlineCssStyleDeclaration>::FromValue(ctx, value, exception_state);
-    } else {
-      if (JS_IsNull(value)) {
-        return static_cast<legacy::LegacyInlineCssStyleDeclaration*>(nullptr);
-      }
-
-      return Converter<legacy::LegacyInlineCssStyleDeclaration>::FromValue(ctx, value, exception_state);
-    }
-  }
-
-  static ElementStyle ArgumentsValue(ExecutingContext* context,
-                                     JSValue value,
-                                     uint32_t argv_index,
-                                     ExceptionState& exception_state) {
-    if (context->isBlinkEnabled()) {
-      if (JS_IsNull(value)) {
-        return static_cast<InlineCssStyleDeclaration*>(nullptr);
-      }
-
-      return Converter<InlineCssStyleDeclaration>::ArgumentsValue(context, value, argv_index, exception_state);
-    } else {
-      if (JS_IsNull(value)) {
-        return static_cast<legacy::LegacyInlineCssStyleDeclaration*>(nullptr);
-      }
-
-      return Converter<legacy::LegacyInlineCssStyleDeclaration>::ArgumentsValue(context, value, argv_index, exception_state);
-    }
-  }
-
-  static JSValue ToValue(JSContext* ctx, ElementStyle value) {
-    return std::visit(MakeVisitor([&ctx](auto* style) {
-                        if (style == nullptr)
-                          return JS_NULL;
-                        return Converter<std::remove_pointer_t<std::decay_t<decltype(style)>>>::ToValue(ctx, style);
-                      }),
-                      value);
-  }
-};
-
 template <>
 struct Converter<WindowComputedStyle> {
   using ImplType = WindowComputedStyle;

bridge/core/api/element.cc

@@ -11,24 +11,20 @@
 #include "core/css/legacy/legacy_inline_css_style_declaration.h"
 #include "core/dom/container_node.h"
 #include "core/dom/element.h"
-#include "foundation/utility/make_visitor.h"
 
 namespace webf {
 
 WebFValue<LegacyCssStyleDeclaration, LegacyCssStyleDeclarationPublicMethods> ElementPublicMethods::Style(Element* ptr) {
   auto* element = static_cast<webf::Element*>(ptr);
   MemberMutationScope member_mutation_scope{element->GetExecutingContext()};
-  auto style = element->style();
+  auto* style_declaration = element->style();
+  if (!style_declaration) {
+    return WebFValue<LegacyCssStyleDeclaration, LegacyCssStyleDeclarationPublicMethods>::Null();
+  }
 
-  return std::visit(
-      MakeVisitor(
-          [&](legacy::LegacyInlineCssStyleDeclaration* styleDeclaration) {
-            WebFValueStatus* status_block = styleDeclaration->KeepAlive();
-            return WebFValue<LegacyCssStyleDeclaration, LegacyCssStyleDeclarationPublicMethods>(
-                styleDeclaration, styleDeclaration->legacyCssStyleDeclarationPublicMethods(), status_block);
-          },
-          [](auto&&) { return WebFValue<LegacyCssStyleDeclaration, LegacyCssStyleDeclarationPublicMethods>::Null(); }),
-      style);
+  WebFValueStatus* status_block = style_declaration->KeepAlive();
+  return WebFValue<LegacyCssStyleDeclaration, LegacyCssStyleDeclarationPublicMethods>(
+      style_declaration, style_declaration->legacyCssStyleDeclarationPublicMethods(), status_block);
 }
 
 void ElementPublicMethods::ToBlob(Element* ptr,

bridge/core/css/blink_inline_style_validation_test.cc

@@ -26,7 +26,7 @@ std::string CommandArg01ToUTF8(const UICommandItem& item) {
   return String(utf16, static_cast<size_t>(item.args_01_length)).ToUTF8String();
 }
 
-std::string SharedNativeStringToUTF8(const SharedNativeString* s) {
+std::string SharedNativeStringToUTF8(const webf::SharedNativeString* s) {
   if (!s || !s->string() || s->length() == 0) {
     return "";
   }
@@ -53,7 +53,7 @@ bool HasSetStyleWithKeyValue(ExecutingContext* context, const std::string& key,
   auto* items = static_cast<UICommandItem*>(pack->data);
   for (int64_t i = 0; i < pack->length; ++i) {
     const UICommandItem& item = items[i];
-    if (item.type == static_cast<int32_t>(UICommand::kSetStyle)) {
+    if (item.type == static_cast<int32_t>(UICommand::kSetInlineStyle)) {
       if (CommandArg01ToUTF8(item) != key) {
         continue;
       }
@@ -79,34 +79,7 @@ bool HasSetStyleWithKeyValue(ExecutingContext* context, const std::string& key,
     if (item.string_01 < 0) {
       value_text = getValueName(static_cast<CSSValueID>(-item.string_01 - 1));
     } else {
-      auto* value_ptr = reinterpret_cast<SharedNativeString*>(static_cast<uintptr_t>(item.string_01));
-      value_text = SharedNativeStringToUTF8(value_ptr);
-    }
-    if (value_text == value) {
-      return true;
-    }
-  }
-  return false;
-}
-
-bool HasSetStyleByIdWithKeyValue(ExecutingContext* context, const std::string& key, const std::string& value) {
-  const CSSPropertyID expected_property_id = CssPropertyID(context, ConvertCamelCaseToKebabCase(key));
-  auto* pack = static_cast<UICommandBufferPack*>(context->uiCommandBuffer()->data());
-  auto* items = static_cast<UICommandItem*>(pack->data);
-  for (int64_t i = 0; i < pack->length; ++i) {
-    const UICommandItem& item = items[i];
-    if (item.type != static_cast<int32_t>(UICommand::kSetStyleById)) {
-      continue;
-    }
-    if (item.args_01_length != static_cast<int32_t>(expected_property_id)) {
-      continue;
-    }
-
-    std::string value_text;
-    if (item.string_01 < 0) {
-      value_text = getValueName(static_cast<CSSValueID>(-item.string_01 - 1));
-    } else {
-      auto* value_ptr = reinterpret_cast<SharedNativeString*>(static_cast<uintptr_t>(item.string_01));
+      auto* value_ptr = reinterpret_cast<webf::SharedNativeString*>(static_cast<uintptr_t>(item.string_01));
       value_text = SharedNativeStringToUTF8(value_ptr);
     }
     if (value_text == value) {
@@ -118,7 +91,7 @@ bool HasSetStyleByIdWithKeyValue(ExecutingContext* context, const std::string& k
 
 }  // namespace
 
-TEST(BlinkCSSStyleDeclarationValidation, RejectsInvalidFontSize) {
+TEST(BlinkCSSStyleDeclarationValidation, ForwardsInvalidFontSizeToDart) {
   bool static errorCalled = false;
   webf::WebFPage::consoleMessageHandler = [](void*, const std::string&, int) {};
 
@@ -137,15 +110,15 @@ TEST(BlinkCSSStyleDeclarationValidation, RejectsInvalidFontSize) {
   const char* set_valid = "document.body.style.fontSize = '18px';";
   env->page()->evaluateScript(set_valid, strlen(set_valid), "vm://", 0);
   TEST_runLoop(context);
-  EXPECT_TRUE(HasSetStyleByIdWithKeyValue(context, "fontSize", "18px"));
+  EXPECT_TRUE(HasSetStyleWithKeyValue(context, "fontSize", "18px"));
 
   context->uiCommandBuffer()->clear();
 
-  // Invalid font-size should be rejected on the native (Blink) CSS side and
-  // thus should not be forwarded to Dart.
+  // Inline style is legacy-only even when Blink CSS is enabled; invalid values
+  // are forwarded to Dart for validation/handling.
   const char* set_invalid = "document.body.style.fontSize = '-1px';";
   env->page()->evaluateScript(set_invalid, strlen(set_invalid), "vm://", 0);
   TEST_runLoop(context);
-  EXPECT_FALSE(HasSetStyleByIdWithKeyValue(context, "fontSize", "-1px"));
+  EXPECT_TRUE(HasSetStyleWithKeyValue(context, "fontSize", "-1px"));
   EXPECT_EQ(errorCalled, false);
 }

bridge/core/css/css_properties.json5

@@ -1103,7 +1103,7 @@
     },
     {
       name: "list-style-type",
-      // Parsing and initial value only – forwarded to Dart via UICommand kSetStyle
+      // Parsing and initial value only – forwarded to Dart via UICommand kSetInlineStyle
       // We don't currently store this on ComputedStyle; values are emitted from the inline
       // property set during style resolution.
       field_template: "keyword",
@@ -1151,7 +1151,7 @@
     // CSS Counters
     {
       name: "counter-reset",
-      // Parsing and initial value only – forwarded to Dart via UICommand kSetStyle
+      // Parsing and initial value only – forwarded to Dart via UICommand kSetInlineStyle
       property_methods: [
         "ParseSingleValue",
         "InitialValue"

bridge/core/css/inline_css_style_declaration_test.cc

@@ -57,7 +57,7 @@ document.body.style.setProperty('--main-color', 'lightblue'); console.assert(doc
 
   UICommandItem& last = ((UICommandItem*)p_buffer_pack->data)[commandSize - 1];
 
-  EXPECT_EQ(last.type, (int32_t)UICommand::kSetStyle);
+  EXPECT_EQ(last.type, (int32_t)UICommand::kSetInlineStyle);
   uint16_t* last_key = (uint16_t*)last.string_01;
 
 //  auto native_str = new webf::SharedNativeString(last_key, last.args_01_length);
@@ -101,4 +101,4 @@ TEST(InlineCSSStyleDeclaration, setNullValue) {
       "console.assert(document.body.style.height === '')";
   env->page()->evaluateScript(code, strlen(code), "vm://", 0);
   EXPECT_EQ(errorCalled, false);
-}
+}