Lazy Parse CSS

third_party/WebKit/Source/core/css/parser/CSSLazyParsingState.cpp

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/css/parser/CSSLazyParsingState.h"
+
+namespace blink {
+
+CSSLazyParsingState::CSSLazyParsingState(const CSSParserContext& context,
+                                         Vector<String> escapedStrings,
+                                         const String& sheetText)
+    : m_context(context),
+      m_escapedStrings(std::move(escapedStrings)),
+      m_sheetText(sheetText) {}
+
+//  Disallow lazy parsing for blocks which have
+//  - before/after in their selector list. This ensures we don't cause a
+//  collectFeatures() when we trigger parsing for attr() functions which would
+//  trigger expensive invalidation propagation.
+//
+//  Note: another optimization might be to disallow lazy parsing for rules which
+//  will end up being empty. This is hard to know without parsing but we may be
+//  able to catch the {}, { } cases. This would be to hit
+//  StyleRule::shouldConsiderForMatchingRules more.
+bool CSSLazyParsingState::shouldLazilyParseProperties(
+    const CSSSelectorList& selectors) {
+  for (const auto* s = selectors.first(); s; s = CSSSelectorList::next(*s)) {
+    const CSSSelector::PseudoType type(s->getPseudoType());
+    if (type == CSSSelector::PseudoBefore || type == CSSSelector::PseudoAfter)
+      return false;
+  }
+  return true;
+}
+
+}  // namespace blink