Source/core/css/StyleInvalidationAnalysis.cpp

/*
 * Copyright (C) 2012 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
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 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE COMPUTER, INC. ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
 * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE COMPUTER, INC. OR
 * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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#include "config.h"
#include "core/css/StyleInvalidationAnalysis.h"

#include "core/css/CSSSelectorList.h"
#include "core/css/StyleRuleImport.h"
#include "core/css/StyleSheetContents.h"
#include "core/dom/ContainerNode.h"
#include "core/dom/Document.h"
#include "core/dom/ElementTraversal.h"
#include "core/dom/shadow/ShadowRoot.h"
#include "core/html/HTMLStyleElement.h"

namespace WebCore {

StyleInvalidationAnalysis::StyleInvalidationAnalysis(const Vector<StyleSheetContents*>& sheets)
    : m_dirtiesAllStyle(false)
{
    for (unsigned i = 0; i < sheets.size() && !m_dirtiesAllStyle; ++i)
        analyzeStyleSheet(sheets[i]);
}

static bool determineSelectorScopes(const CSSSelectorList& selectorList, HashSet<StringImpl*>& idScopes, HashSet<StringImpl*>& classScopes)
{
    for (const CSSSelector* selector = selectorList.first(); selector; selector = CSSSelectorList::next(selector)) {
        const CSSSelector* scopeSelector = 0;
        // This picks the widest scope, not the narrowest, to minimize the number of found scopes.
        for (const CSSSelector* current = selector; current; current = current->tagHistory()) {
            // Prefer ids over classes.
            if (current->m_match == CSSSelector::Id)
                scopeSelector = current;
            else if (current->m_match == CSSSelector::Class && (!scopeSelector || scopeSelector->m_match != CSSSelector::Id))
                scopeSelector = current;
            CSSSelector::Relation relation = current->relation();
            if (relation != CSSSelector::Descendant && relation != CSSSelector::Child && relation != CSSSelector::SubSelector)
                break;
        }
        if (!scopeSelector)
            return false;
        ASSERT(scopeSelector->m_match == CSSSelector::Class || scopeSelector->m_match == CSSSelector::Id);
        if (scopeSelector->m_match == CSSSelector::Id)
            idScopes.add(scopeSelector->value().impl());
        else
            classScopes.add(scopeSelector->value().impl());
    }
    return true;
}

static bool hasDistributedRule(StyleSheetContents* styleSheetContents)
{
    const Vector<RefPtr<StyleRuleBase> >& rules = styleSheetContents->childRules();
    for (unsigned i = 0; i < rules.size(); i++) {
        const StyleRuleBase* rule = rules[i].get();
        if (!rule->isStyleRule())
            continue;

        const StyleRule* styleRule = toStyleRule(rule);
        const CSSSelectorList& selectorList = styleRule->selectorList();
        for (size_t selectorIndex = 0; selectorIndex != kNotFound; selectorIndex = selectorList.indexOfNextSelectorAfter(selectorIndex)) {
            if (selectorList.hasShadowDistributedAt(selectorIndex))
                return true;
        }
    }
    return false;
}

static bool hasAtHostRule(StyleSheetContents* styleSheetContents)
{
    const Vector<RefPtr<StyleRuleBase> >& rules = styleSheetContents->childRules();
    for (unsigned i = 0; i < rules.size(); i++) {
        const StyleRuleBase* rule = rules[i].get();
        if (rule->isHostRule())
            return true;
    }
    return false;
}

static Node* determineScopingNodeForStyleScoped(HTMLStyleElement* ownerElement, StyleSheetContents* styleSheetContents)
{
    ASSERT(ownerElement && ownerElement->isRegisteredAsScoped());

    if (ownerElement->isInShadowTree()) {
        if (hasDistributedRule(styleSheetContents)) {
            ContainerNode* scope = ownerElement;
            do {
                scope = scope->containingShadowRoot()->shadowHost();
            } while (scope->isInShadowTree());

            return scope;
        }
        if (ownerElement->isRegisteredAsScoped() && hasAtHostRule(styleSheetContents))
            return ownerElement->containingShadowRoot()->shadowHost();
    }

    return ownerElement->isRegisteredInShadowRoot() ? ownerElement->containingShadowRoot()->shadowHost() : ownerElement->parentNode();
}

static bool ruleAdditionMightRequireDocumentStyleRecalc(StyleRuleBase* rule)
{
    // This funciton is conservative. We only return false when we know that
    // the added @rule can't require style recalcs.
    switch (rule->type()) {
    case StyleRule::Import: // Whatever we import should do its own analysis, we don't need to invalidate the document here!
    case StyleRule::Keyframes: // Keyframes never cause style invalidations and are handled during sheet insertion.
    case StyleRule::Page: // Page rules apply only during printing, we force a full-recalc before printing.
        return false;

    case StyleRule::Media: // If the media rule doesn't apply, we could avoid recalc.
    case StyleRule::FontFace: // If the fonts aren't in use, we could avoid recalc.
    case StyleRule::Supports: // If we evaluated the supports-clause we could avoid recalc.
    case StyleRule::Viewport: // If the viewport doesn't match, we could avoid recalcing.
    // FIXME: Unclear if any of the rest need to cause style recalc:
    case StyleRule::Region:
    case StyleRule::Filter:
    case StyleRule::HostInternal:
        return true;

    // These should all be impossible to reach:
    case StyleRule::Unknown:
    case StyleRule::Charset:
    case StyleRule::Keyframe:
    case StyleRule::Style:
        break;
    }
    ASSERT_NOT_REACHED();
    return true;
}

void StyleInvalidationAnalysis::analyzeStyleSheet(StyleSheetContents* styleSheetContents)
{
    ASSERT(!styleSheetContents->isLoading());

    // See if all rules on the sheet are scoped to some specific ids or classes.
    // Then test if we actually have any of those in the tree at the moment.
    const Vector<RefPtr<StyleRuleImport> >& importRules = styleSheetContents->importRules();
    for (unsigned i = 0; i < importRules.size(); ++i) {
        if (!importRules[i]->styleSheet())
            continue;
        analyzeStyleSheet(importRules[i]->styleSheet());
        if (m_dirtiesAllStyle)
            return;
    }
    if (styleSheetContents->hasSingleOwnerNode()) {
        Node* ownerNode = styleSheetContents->singleOwnerNode();
        if (ownerNode && ownerNode->hasTagName(HTMLNames::styleTag) && toHTMLStyleElement(ownerNode)->isRegisteredAsScoped()) {
            m_scopingNodes.append(determineScopingNodeForStyleScoped(toHTMLStyleElement(ownerNode), styleSheetContents));
            return;
        }
    }

    const Vector<RefPtr<StyleRuleBase> >& rules = styleSheetContents->childRules();
    for (unsigned i = 0; i < rules.size(); i++) {
        StyleRuleBase* rule = rules[i].get();
        if (!rule->isStyleRule()) {
            if (ruleAdditionMightRequireDocumentStyleRecalc(rule)) {
                m_dirtiesAllStyle = true;
                return;
            }
            continue;
        }
        StyleRule* styleRule = toStyleRule(rule);
        if (!determineSelectorScopes(styleRule->selectorList(), m_idScopes, m_classScopes)) {
            m_dirtiesAllStyle = true;
            return;
        }
    }
}

static bool elementMatchesSelectorScopes(const Element* element, const HashSet<StringImpl*>& idScopes, const HashSet<StringImpl*>& classScopes)
{
    if (!idScopes.isEmpty() && element->hasID() && idScopes.contains(element->idForStyleResolution().impl()))
        return true;
    if (classScopes.isEmpty() || !element->hasClass())
        return false;
    const SpaceSplitString& classNames = element->classNames();
    for (unsigned i = 0; i < classNames.size(); ++i) {
        if (classScopes.contains(classNames[i].impl()))
            return true;
    }
    return false;
}

void StyleInvalidationAnalysis::invalidateStyle(Document* document)
{
    ASSERT(!m_dirtiesAllStyle);

    if (!m_scopingNodes.isEmpty()) {
        for (unsigned i = 0; i < m_scopingNodes.size(); ++i)
            m_scopingNodes.at(i)->setNeedsStyleRecalc();
    }

    if (m_idScopes.isEmpty() && m_classScopes.isEmpty())
        return;
    Element* element = ElementTraversal::firstWithin(document);
    while (element) {
        if (elementMatchesSelectorScopes(element, m_idScopes, m_classScopes)) {
            element->setNeedsStyleRecalc();
            // The whole subtree is now invalidated, we can skip to the next sibling.
            element = ElementTraversal::nextSkippingChildren(element);
            continue;
        }
        element = ElementTraversal::next(element);
    }
}

}