CSS Properties and Values API: Implement computation / computational independence

third_party/WebKit/Source/core/css/PropertyRegistration.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/PropertyRegistration.h"
 
 #include "core/css/CSSSyntaxDescriptor.h"
+#include "core/css/CSSValueList.h"
 #include "core/css/CSSVariableReferenceValue.h"
 #include "core/css/PropertyDescriptor.h"
 #include "core/css/PropertyRegistry.h"
 #include "core/css/parser/CSSVariableParser.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
 #include "core/dom/StyleChangeReason.h"
 
 namespace blink {
 
-static bool computationallyIdempotent(const CSSValue& value)
+static bool computationallyIndependent(const CSSValue& value)
 {
-    // TODO(timloh): Implement this
+    DCHECK(!value.isCSSWideKeyword());
+
+    if (value.isVariableReferenceValue())
+        return !toCSSVariableReferenceValue(value).variableDataValue()->needsVariableResolution();
+
+    if (value.isValueList()) {
+        for (const CSSValue* innerValue : toCSSValueList(value)) {
+            if (!computationallyIndependent(*innerValue))
+                return false;
+        }
+        return true;
+    }
+
+    if (value.isPrimitiveValue()) {
+        const CSSPrimitiveValue& primitiveValue = toCSSPrimitiveValue(value);
+        if (!primitiveValue.isLength() && !primitiveValue.isCalculatedPercentageWithLength())
+            return true;
+
+        CSSPrimitiveValue::CSSLengthArray lengthArray;
+        primitiveValue.accumulateLengthArray(lengthArray);
+        for (size_t i = 0; i < lengthArray.values.size(); i++) {
+            if (lengthArray.typeFlags.get(i)
+                && i != CSSPrimitiveValue::UnitTypePixels
+                && i != CSSPrimitiveValue::UnitTypePercentage)
+                return false;
+        }
+        return true;
+    }
+
+    // TODO(timloh): Images and transform-function values can also contain lengths.
+
     return true;
 }
 
 void PropertyRegistration::registerProperty(ExecutionContext* executionContext, const PropertyDescriptor& descriptor, ExceptionState& exceptionState)
 {
     // Bindings code ensures these are set.
     DCHECK(descriptor.hasName());
     DCHECK(descriptor.hasInherits());
     DCHECK(descriptor.hasSyntax());
 
@@ skipping 15 matching lines @@
         exceptionState.throwDOMException(SyntaxError, "The syntax provided is not a valid custom property syntax.");
         return;
     }
 
     if (descriptor.hasInitialValue()) {
         const CSSValue* initial = syntaxDescriptor.parse(descriptor.initialValue());
         if (!initial) {
             exceptionState.throwDOMException(SyntaxError, "The initial value provided does not parse for the given syntax.");
             return;
         }
-        if (!computationallyIdempotent(*initial)) {
-            exceptionState.throwDOMException(SyntaxError, "The initial value provided is not computationally idempotent.");
+        if (!computationallyIndependent(*initial)) {
+            exceptionState.throwDOMException(SyntaxError, "The initial value provided is not computationally independent.");
             return;
         }
         registry.registerProperty(atomicName, syntaxDescriptor, descriptor.inherits(), initial);
     } else {
         if (!syntaxDescriptor.isTokenStream()) {
             exceptionState.throwDOMException(SyntaxError, "An initial value must be provided if the syntax is not '*'");
             return;
         }
         registry.registerProperty(atomicName, syntaxDescriptor, descriptor.inherits(), nullptr);
     }
@@ skipping 10 matching lines @@
     if (!registry.registration(atomicProperty)) {
         exceptionState.throwDOMException(NotFoundError, "CSS.unregisterProperty() called with non-registered property " + property);
         return;
     }
     registry.unregisterProperty(atomicProperty);
 
     document->setNeedsStyleRecalc(SubtreeStyleChange, StyleChangeReasonForTracing::create(StyleChangeReason::PropertyUnregistration));
 }
 
 } // namespace blink