[webkit-dev] Null value for QualifiedName

[Ryosuke Niwa]

Greetings all,

While working on the bug 44288<https://bugs.webkit.org/show_bug.cgi?id=44288>,
it came to my attention that
the default constructor of QualifiedName is behind a
flag QNAME_DEFAULT_CONSTRUCTOR,
and I can't find a qualified name that stands for invalid / null value.

Is there any designated qualified name object that stands for invalid / null
value?

Invalid / null qualified name will be useful in the context like:
http://trac.webkit.org/browser/trunk/WebCore/editing/markup.cpp?rev=65854#L488
:

void MarkupAccumulator::appendText(Vector<UChar>& out, Text* text)
{
    const QualifiedName* parentName = 0;
    if (text->parentElement())
        parentName =
&static_cast<Element*>(text->parentElement())->tagQName();

    if (parentName && (*parentName == scriptTag || *parentName == styleTag
|| *parentName == xmpTag)) {
        appendUCharRange(out, ucharRange(text, m_range));
        return;
    }

    if (!shouldAnnotate() || (parentName && *parentName == textareaTag)) {
        appendEscapedContent(out, ucharRange(text, m_range),
text->document()->isHTMLDocument());
        return;
    }
...

where I obtain the qualified name of the parent element which may or may not
exist.
If we had a null qualified name, above code can be re-written as:

void MarkupAccumulator::appendText(Vector<UChar>& out, Text* text)
{
    QualifiedName parentName = nullName;
    if (text->parentElement())
        parentName =
&static_cast<Element*>(text->parentElement())->tagQName();

    if (parentName == scriptTag || parentName == styleTag || parentName ==
xmpTag) {
        appendUCharRange(out, ucharRange(text, m_range));
        return;
    }

    if (!shouldAnnotate() || parentName == textareaTag) {
        appendEscapedContent(out, ucharRange(text, m_range),
text->document()->isHTMLDocument());
        return;
    }
...

IMHO, new code is easier to read and has very little drawbacks (possible
slowdown use to construction of QualifiedName).
I could have used htmlTag or any other qualified name different from the
four names used above,
but that wouldn't be semantically correct.

Ryosuke Niwa
Software Engineer
Google Inc.
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