Source/WebCore/css/CSSVariableReferenceValue.cpp

// Copyright 2015 The Chromium Authors. All rights reserved.
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#include "config.h"
#include "CSSVariableReferenceValue.h"

#include "CSSCustomPropertyValue.h"
#include "CSSParserTokenRange.h"
#include "CSSPropertyParser.h"
#include "CSSRegisteredCustomProperty.h"
#include "CSSVariableData.h"
#include "ConstantPropertyMap.h"
#include "CustomFunctionRegistry.h"
#include "Document.h"
#include "RenderStyle+GettersInlines.h"
#include "StyleBuilder.h"
#include "StyleCustomPropertyRegistry.h"
#include "StyleResolver.h"
#include "StyleScope.h"

namespace WebCore {

CSSVariableReferenceValue::CSSVariableReferenceValue(Ref<CSSVariableData>&& data)
    : CSSValue(ClassType::VariableReference)
    , m_data(WTF::move(data))
{
    cacheSimpleReference();
}

Ref<CSSVariableReferenceValue> CSSVariableReferenceValue::create(const CSSParserTokenRange& range, const CSSParserContext& context)
{
    return adoptRef(*new CSSVariableReferenceValue(CSSVariableData::create(range, context)));
}

Ref<CSSVariableReferenceValue> CSSVariableReferenceValue::create(Ref<CSSVariableData>&& data)
{
    return adoptRef(*new CSSVariableReferenceValue(WTF::move(data)));
}

bool CSSVariableReferenceValue::equals(const CSSVariableReferenceValue& other) const
{
    return arePointingToEqualData(m_data, other.m_data);
}

String CSSVariableReferenceValue::customCSSText(const CSS::SerializationContext&) const
{
    if (m_stringValue.isNull())
        m_stringValue = m_data->serialize();
    return m_stringValue;
}

const CSSParserContext& CSSVariableReferenceValue::context() const
{
    return m_data->context();
}

auto CSSVariableReferenceValue::resolveVariableFallback(const AtomString& variableName, CSSParserTokenRange range, CSSValueID functionId, Style::Builder& builder) const -> std::pair<FallbackResult, Vector<CSSParserToken>>
{
    ASSERT(range.atEnd() || range.peek().type() == CommaToken);

    if (range.atEnd())
        return { FallbackResult::None, { } };

    range.consumeIncludingWhitespace();

    auto tokens = resolveTokenRange(range, builder);

    if (functionId == CSSValueVar) {
        auto* registered = builder.state().document().customPropertyRegistry().get(variableName);
        if (registered && !registered->syntax.isUniversal()) {
            // https://drafts.css-houdini.org/css-properties-values-api/#fallbacks-in-var-references
            // The fallback value must match the syntax definition of the custom property being referenced,
            // otherwise the declaration is invalid at computed-value time
            if (!tokens || !CSSPropertyParser::isValidCustomPropertyValueForSyntax(registered->syntax, *tokens, context()))
                return { FallbackResult::Invalid, { } };

            return { FallbackResult::Valid, WTF::move(*tokens) };
        }
    }

    if (!tokens)
        return { FallbackResult::None, { } };

    return { FallbackResult::Valid, WTF::move(*tokens) };
}

static const Style::CustomProperty* propertyValueForVariableName(const AtomString& variableName, CSSValueID functionId, Style::Builder& builder)
{
    if (functionId == CSSValueEnv)
        return builder.state().document().constantProperties().values().get(variableName);

    // Apply this variable first, in case it is still unresolved
    builder.applyCustomProperty(variableName);

    return builder.state().checkedStyle()->customPropertyValue(variableName);
}

bool CSSVariableReferenceValue::resolveVariableReference(CSSParserTokenRange range, CSSValueID functionId, Vector<CSSParserToken>& tokens, Style::Builder& builder) const
{
    ASSERT(functionId == CSSValueVar || functionId == CSSValueEnv);

    range.consumeWhitespace();
    ASSERT(range.peek().type() == IdentToken);
    auto variableName = range.consumeIncludingWhitespace().value().toAtomString();

    // Fallback has to be resolved even when not used to detect cycles and invalid syntax.
    auto [fallbackResult, fallbackTokens] = resolveVariableFallback(variableName, range, functionId, builder);
    if (fallbackResult == FallbackResult::Invalid)
        return false;

    RefPtr property = propertyValueForVariableName(variableName, functionId, builder);

    if (!property || property->isGuaranteedInvalid()) {
        if (fallbackTokens.size() > maxSubstitutionTokens)
            return false;

        if (fallbackResult == FallbackResult::Valid) {
            tokens.appendVector(fallbackTokens);
            return true;
        }
        return false;
    }

    if (property->tokens().size() > maxSubstitutionTokens)
        return false;

    tokens.appendVector(property->tokens());
    return true;
}

bool CSSVariableReferenceValue::evaluateDashedFunction(StringView functionName, CSSParserTokenRange, Vector<CSSParserToken>& tokens, Style::Builder& builder) const
{
    // https://drafts.csswg.org/css-mixins/#evaluating-custom-functions

    if (!builder.state().element())
        return false;

    auto scopedFunctionName = Style::ScopedName { functionName.toAtomString(), builder.state().styleScopeOrdinal() };

    CheckedPtr element = builder.state().element();
    auto customFunction = Style::Scope::resolveTreeScopedReference(*element, scopedFunctionName, [](const Style::Scope& scope, const AtomString& name) -> CheckedPtr<const Style::CustomFunction> {
        RefPtr resolver = scope.resolverIfExists();
        CheckedPtr registry = resolver ? resolver->customFunctionRegistry() : nullptr;
        return registry ? registry->functionForName(name) : nullptr;
    });

    if (!customFunction)
        return false;

    // FIXME: Evaluate the function instead of just substituting.

    auto properties = customFunction->properties;
    auto resultValue = dynamicDowncast<CSSCustomPropertyValue>(properties->getPropertyCSSValue(CSSPropertyResult));
    if (!resultValue)
        return false;

    auto data = resultValue->asVariableData();
    tokens.appendVector(data->tokens());
    return true;
}

std::optional<Vector<CSSParserToken>> CSSVariableReferenceValue::resolveTokenRange(CSSParserTokenRange range, Style::Builder& builder) const
{
    Vector<CSSParserToken> tokens;
    bool success = true;
    while (!range.atEnd()) {
        auto token = range.peek();
        if (token.type() == FunctionToken) {
            auto functionId = token.functionId();
            if (functionId == CSSValueVar || functionId == CSSValueEnv) {
                if (!resolveVariableReference(range.consumeBlock(), functionId, tokens, builder))
                    success = false;
                continue;
            }
            if (isCustomPropertyName(token.value())) {
                // <dashed-function>
                if (!evaluateDashedFunction(token.value(), range.consumeBlock(), tokens, builder))
                    success = false;
                continue;
            }
        }
        tokens.append(range.consume());
    }
    if (!success)
        return { };

    return tokens;
}

void CSSVariableReferenceValue::cacheSimpleReference()
{
    ASSERT(!m_simpleReference);

    auto range = m_data->tokenRange();

    auto functionId = range.peek().functionId();
    if (functionId != CSSValueVar && functionId != CSSValueEnv)
        return;

    auto variableRange = range.consumeBlock();
    if (!range.atEnd())
        return;

    variableRange.consumeWhitespace();

    auto variableName = variableRange.consumeIncludingWhitespace().value().toAtomString();

    // No fallback support on this path.
    if (!variableRange.atEnd())
        return;

    m_simpleReference = SimpleReference { variableName, functionId };
}

RefPtr<CSSVariableData> CSSVariableReferenceValue::tryResolveSimpleReference(Style::Builder& builder) const
{
    if (!m_simpleReference)
        return nullptr;

    // Shortcut for the simple common case of property:var(--foo)

    RefPtr property = propertyValueForVariableName(m_simpleReference->name, m_simpleReference->functionId, builder);
    if (!property || !std::holds_alternative<Ref<CSSVariableData>>(property->value()))
        return nullptr;

    return std::get<Ref<CSSVariableData>>(property->value()).ptr();
}

RefPtr<CSSVariableData> CSSVariableReferenceValue::resolveVariableReferences(Style::Builder& builder) const
{
    if (auto data = tryResolveSimpleReference(builder))
        return data;

    auto resolvedTokens = resolveTokenRange(m_data->tokenRange(), builder);
    if (!resolvedTokens)
        return nullptr;

    return CSSVariableData::create(*resolvedTokens, context());
}

RefPtr<CSSValue> CSSVariableReferenceValue::resolveSingleValue(Style::Builder& builder, CSSPropertyID propertyID) const
{
    if (!resolveAndCacheValue(builder, [this, propertyID](auto data) {
        m_cachedValue = CSSPropertyParser::parseStylePropertyLonghand(propertyID, data->tokens(), context());
#if ASSERT_ENABLED
        m_cachePropertyID = propertyID;
#endif
    }))
        return nullptr;

    ASSERT(m_cachePropertyID == propertyID);
    return m_cachedValue;
}

} // namespace WebCore