CSS Custom Properties (Variables)

Source/core/css/resolver/CSSVariableResolver.cpp

+// Copyright 2015 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 "config.h"
+#include "core/css/resolver/CSSVariableResolver.h"
+
+#include "core/CSSPropertyNames.h"
+#include "core/CSSValueKeywords.h"
+#include "core/StyleBuilderFunctions.h"
+#include "core/css/CSSVariableData.h"
+#include "core/css/parser/CSSParserToken.h"
+#include "core/css/parser/CSSParserTokenRange.h"
+#include "core/css/parser/CSSParserValues.h"
+#include "core/css/parser/CSSPropertyParser.h"
+#include "core/css/resolver/StyleResolverState.h"
+#include "core/style/StyleVariableData.h"
+#include "wtf/Vector.h"
+
+namespace blink {
+
+static bool isVariableReferenceToken(CSSParserToken& token)
+{
+    return token.type() == FunctionToken && token.valueEqualsIgnoringCase("var");
+}
+
+// TODO(leviw): These will get moved out of StyleBuilder
+// TODO(leviw): Validation should no longer be required here
+static bool findEndOfVariableReference(Vector<CSSParserToken>& resolvedTokens, unsigned startOffset, unsigned& end, unsigned& commaLocation)
+{
+    end = 0;
+    commaLocation = 0;
+    unsigned bracketCount = 0;
+    bool validSyntax = true;
+    for (unsigned i = startOffset; i < resolvedTokens.size(); ++i) {
+        CSSParserTokenType type = resolvedTokens[i].type();
+
+        if (type == CommaToken && !commaLocation) {
+            commaLocation = i;
+        } else if (type == LeftParenthesisToken || type == FunctionToken) {
+            bracketCount++;
+        } else if (type == RightParenthesisToken) {
+            if (bracketCount) {
+                bracketCount--;
+            } else {
+                end = i;
+                break;
+            }
+        } else if (type != WhitespaceToken && !commaLocation) {
+            // We need content after a comma for valid syntax, but if it occurs
+            // before a comma its invalid.
+            validSyntax = commaLocation;
+        }
+    }
+    if (!end || !validSyntax) {
+        end = resolvedTokens.size() - 1;
+        return false;
+    }
+    return true;
+}
+
+unsigned CSSVariableResolver::resolveVariableTokensRecursive(Vector<CSSParserToken>& resolvedTokens, unsigned startOffset)
+{
+    ASSERT(startOffset);
+    // There should be at least 2 tokens after the start position: a the variable name and the close bracket
+    if (resolvedTokens.size() < startOffset + 1)
+        return -1;
+
+    unsigned commaLocation, end;
+
+    // Find the variable location
+    unsigned variableLocation = 0;
+    for (unsigned i = startOffset; i < resolvedTokens.size(); ++i) {
+        if (resolvedTokens[i].type() == IdentToken) {
+            variableLocation = i;
+            break;
+        }
+        if (resolvedTokens[i].type() != WhitespaceToken) {
+            findEndOfVariableReference(resolvedTokens, i, end, commaLocation);
+            unsigned length = end - startOffset + 2;
+            resolvedTokens.remove(startOffset - 1, length);
+            return -1;
+        }
+    }
+
+    // Find default value and match braces
+    if (!findEndOfVariableReference(resolvedTokens, variableLocation + 1, end, commaLocation)) {
+        unsigned length = end - startOffset + 2;
+        resolvedTokens.remove(startOffset - 1, length);
+        return -1;
+    }
+
+    unsigned length = end - startOffset + 2;
+    unsigned varFunctionPosition = startOffset - 1;
+
+    AtomicString variableName = resolvedTokens[variableLocation].value();
+
+    if (m_variablesSeen.contains(variableName)) {
+        m_cycleDetected = true;
+        resolvedTokens.clear();
+        return 0;
+    }
+
+    CSSVariableData* variableData = m_styleVariableData ? m_styleVariableData->getVariable(variableName) : nullptr;
+    if (variableData) {
+        Vector<CSSParserToken>& tokens = variableData->tokens();
+        if (variableData->needsVariableResolution()) {
+            m_variablesSeen.add(variableName);
+            resolveVariableReferencesFromTokens(tokens);
+            m_variablesSeen.remove(variableName);
+        }
+        if (tokens.size()) {
+            resolvedTokens.remove(startOffset - 1, length);
+            resolvedTokens.insert(startOffset - 1, tokens);
+            return tokens.size();
+        }
+    }
+
+    // Fallback on default value if present
+    if (!commaLocation || m_cycleDetected) {
+        resolvedTokens.clear();
+        return 0;
+    }
+
+    // Move the tokens to the beginning of the variable reference
+    unsigned defaultValueOffset = commaLocation + 1;
+    unsigned defaultValueLength = end - commaLocation - 1;
+    for (unsigned i = 0; i < defaultValueLength; ++i)
+        resolvedTokens[varFunctionPosition + i] = resolvedTokens[defaultValueOffset + i];
+    resolvedTokens.remove(varFunctionPosition + defaultValueLength, length - defaultValueLength);
+
+    resolveVariableReferencesFromTokens(resolvedTokens);
+
+    return resolvedTokens.size();
+}
+
+void CSSVariableResolver::resolveVariableReferencesFromTokens(Vector<CSSParserToken>& tokens)

[Timothy Loh, 2015/07/23 08:11:47]

Probably nicer to take a CSSParserTokenRange and Vector<CSSParserToken>&
(initially empty), and return a bool.

+{
+    for (unsigned i = 0; i < tokens.size(); ++i) {
+        if (isVariableReferenceToken(tokens[i])) {
+            unsigned validTokens = resolveVariableTokensRecursive(tokens, i + 1);
+            if (validTokens < 1 || m_cycleDetected) {
+                tokens.clear();
+                break;
+            }
+            i += validTokens - 1;
+        }
+    }
+}
+
+void CSSVariableResolver::resolveAndApplyVariableReferences(StyleResolverState& state, CSSPropertyID id, CSSPrimitiveValue* value)
+{
+    // TODO(leviw): This should be a stack
+    Vector<CSSParserToken> tokens = value->getVariableDataValue()->tokens();
+
+    CSSVariableResolver resolver(state.style()->variables());
+
+    resolver.resolveVariableReferencesFromTokens(tokens);
+
+    if (!tokens.size())
+        return;
+
+    CSSParserContext context(HTMLStandardMode, 0);
+
+    WillBeHeapVector<CSSProperty, 256> parsedProperties;
+
+    bool usesRemUnits;
+
+    // TODO(leviw): respect the usesRemUnits flag.
+    CSSParserValueList valueList(CSSParserTokenRange(tokens), usesRemUnits);
+
+    if (!valueList.size())
+        return;
+
+    CSSPropertyParser::parseValue(id, false, &valueList, context, parsedProperties, StyleRule::Type::Style);
+
+    unsigned parsedPropertiesCount = parsedProperties.size();
+    for (unsigned i = 0; i < parsedPropertiesCount; ++i)
+        StyleBuilder::applyProperty(parsedProperties[i].id(), state, parsedProperties[i].value());
+}
+
+void CSSVariableResolver::resolveVariableDefinitions(StyleResolverState& state)
+{
+    StyleVariableData* variables = state.style()->variables();
+    if (!variables)
+        return;
+
+    // TODO(leviw): Skip resolving definitions without references.
+    for (auto& variable : variables->m_data) {
+        if (!variable.value->needsVariableResolution())
+            continue;
+        Vector<CSSParserToken>& tokens = variable.value->tokens();
+
+        CSSVariableResolver resolver(variables, variable.key);
+        resolver.resolveVariableReferencesFromTokens(tokens);
+
+        variable.value->setNeedsVariableResolution(false);

[Timothy Loh, 2015/07/23 08:11:47]

I think this will fail cases like:

#parent { --foo: 1; --bar: var(--foo); }
#child { --foo: 2; } /* bar should get 2, but ends up with 1? */

+    }
+}
+
+CSSVariableResolver::CSSVariableResolver(const StyleVariableData* styleVariableData)
+    : m_styleVariableData(styleVariableData)
+    , m_cycleDetected(false)
+{
+}
+
+CSSVariableResolver::CSSVariableResolver(const StyleVariableData* styleVariableData, AtomicString& variable)
+    : m_styleVariableData(styleVariableData)
+    , m_cycleDetected(false)
+{
+    m_variablesSeen.add(variable);
+}
+
+} // namespace blink