className should be allowed to be a whitespace-only string

third_party/WebKit/Source/core/dom/Element.cpp

Index: third_party/WebKit/Source/core/dom/Element.cpp
diff --git a/third_party/WebKit/Source/core/dom/Element.cpp b/third_party/WebKit/Source/core/dom/Element.cpp
index 9034a842ff08eed765667e4d3dfa4a467b18e33b..d0439217f457a1e59aab37db2b125f00e88c0413 100644
--- a/third_party/WebKit/Source/core/dom/Element.cpp
+++ b/third_party/WebKit/Source/core/dom/Element.cpp
@@ -1229,10 +1229,11 @@ inline void Element::attributeChangedFromParserOrByCloning(const QualifiedName&
 }
 
 template <typename CharacterType>
-static inline bool classStringHasClassName(const CharacterType* characters, unsigned length)
+static inline bool classStringHasClassName(const CharacterType* characters, unsigned length, bool& isWhiteSpaceOnly)

[tkent, 2015/10/08 23:20:12]

We should introduce an enum, and this function should return it.

e.g.

enum class ClassStringContent {
    Empty,
    WhiteSpaceOnly,
    HasClasses
};

template <typename CharacterType>
static inline ClassStringContent analyzeClassString(const CharacterType*
characters, unsigned length) ...

 {
     ASSERT(length > 0);
 
+    isWhiteSpaceOnly = false;
     unsigned i = 0;
     do {
         if (isNotHTMLSpace<CharacterType>(characters[i]))
@@ -1240,10 +1241,13 @@ static inline bool classStringHasClassName(const CharacterType* characters, unsi
         ++i;
     } while (i < length);
 
+    if (i == length)
+        isWhiteSpaceOnly = true;
+
     return i < length;
 }
 
-static inline bool classStringHasClassName(const AtomicString& newClassString)
+static inline bool classStringHasClassName(const AtomicString& newClassString, bool& isWhiteSpaceOnly)
 {
     unsigned length = newClassString.length();
 
@@ -1251,8 +1255,8 @@ static inline bool classStringHasClassName(const AtomicString& newClassString)
         return false;
 
     if (newClassString.is8Bit())
-        return classStringHasClassName(newClassString.characters8(), length);
-    return classStringHasClassName(newClassString.characters16(), length);
+        return classStringHasClassName(newClassString.characters8(), length, isWhiteSpaceOnly);
+    return classStringHasClassName(newClassString.characters16(), length, isWhiteSpaceOnly);
 }
 
 void Element::classAttributeChanged(const AtomicString& newClassString)
@@ -1261,8 +1265,10 @@ void Element::classAttributeChanged(const AtomicString& newClassString)
     bool testShouldInvalidateStyle = inActiveDocument() && styleResolver && styleChangeType() < SubtreeStyleChange;
 
     ASSERT(elementData());
-    if (classStringHasClassName(newClassString)) {
-        const bool shouldFoldCase = document().inQuirksMode();
+
+    bool isWhiteSpaceOnlyClassname;

[tkent, 2015/10/08 23:20:12]

This variable needs to be initialized, or classStringHasClassName() should set
false in i!=length case.

+    const bool shouldFoldCase = document().inQuirksMode();
+    if (classStringHasClassName(newClassString, isWhiteSpaceOnlyClassname)) {
         const SpaceSplitString oldClasses = elementData()->classNames();
         elementData()->setClass(newClassString, shouldFoldCase);
         const SpaceSplitString& newClasses = elementData()->classNames();
@@ -1272,7 +1278,10 @@ void Element::classAttributeChanged(const AtomicString& newClassString)
         const SpaceSplitString& oldClasses = elementData()->classNames();
         if (testShouldInvalidateStyle)
             document().styleEngine().classChangedForElement(oldClasses, *this);
-        elementData()->clearClass();
+        if (isWhiteSpaceOnlyClassname)
+            elementData()->setClass(newClassString, shouldFoldCase);
+        else
+            elementData()->clearClass();
     }
 
     if (hasRareData())
@@ -1297,7 +1306,8 @@ bool Element::shouldInvalidateDistributionWhenAttributeChanged(ElementShadow* el
 
     if (name == HTMLNames::classAttr) {
         const AtomicString& newClassString = newValue;
-        if (classStringHasClassName(newClassString)) {
+        bool isWhiteSpaceOnlyClassname;
+        if (classStringHasClassName(newClassString, isWhiteSpaceOnlyClassname)) {
             const SpaceSplitString& oldClasses = elementData()->classNames();
             const SpaceSplitString newClasses(newClassString, document().inQuirksMode() ? SpaceSplitString::ShouldFoldCase : SpaceSplitString::ShouldNotFoldCase);
             if (featureSet.checkSelectorsForClassChange(oldClasses, newClasses))