QCSS: Support Qt 5-style integer property selectors

In Qt 5 style sheets, objects could be selected by an enum-type property
using the integer value of the enum value, e.g

QToolButton[popupMode="1"] { ... }

In Qt 6, the the new meta type system and QVariant implementation enabled
QVariant::toString to return the string representation of the enum value
instead for a property containing an enum. Since QStyleSheetStyle's
attribute matching is string based, this breaks the Qt 5 style selector,
and QCSS code instead needs to use e.g.

QToolButton[popupMode=MenuButtonPopup] { ... }

While the new syntax is arguably preferable, this is an unintentional
change that silently breaks style sheet code (no error or warning at
compile- or run-time).

To support Qt 5-style selectors, we have to change the StyleSelector
interface of the QCssParser API so that we can pass through what type
of value the attribute extractor should return; if an integer string "1"
is provided, then we need to compare the enum integer value; if the
string provided does not represent a number, then we need to compare the
name of the enum value.

Since the pure virtual attribute() method that needs to be implemented
to extract the attribute value of the node is implemented in modules
outside qtbase, add a second virtual method that takes the entire
QCss::AttributeSelector, which includes the value to match. Extractor
implementations can use it to evaluate which type of data to return for
an exact match. The default implementation calls the old attribute()
method so that existing StyleSelector implementations continue to work.

Make the respective change in the QStyleSheetStyleSelector, and simplify
the surrounding code. Adjust other StyleSelector implemnentations in
qtbase. As a drive-by, remove the superfluous virtual declaration from
those overrides.

Once submodules are adjusted to override this virtual function instead
of the (now no longer pure) virtual attribute() method, that method can
be removed.

Pick-to: 6.3 6.2
Fixes: QTBUG-99642
Change-Id: I9a2b3498f77bf7cab5e90980b7dab2f621d3d859
Reviewed-by: Oliver Eftevaag <oliver.eftevaag@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

1 files changed, 34 insertions, 20 deletions

diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 1449def8c5..b799948933 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -1570,39 +1570,53 @@ public:
         } while (metaObject != nullptr);
         return result;
     }
-    QString attribute(NodePtr node, const QString& name) const override
+    QString attributeValue(NodePtr node, const QCss::AttributeSelector& aSelector) const override
     {
         if (isNullNode(node))
             return QString();
 
+        const QString &name = aSelector.name;
         QHash<QString, QString> &cache = m_attributeCache[OBJECT_PTR(node)];
         QHash<QString, QString>::const_iterator cacheIt = cache.constFind(name);
         if (cacheIt != cache.constEnd())
             return cacheIt.value();
 
+        QVariant value;
+        QString valueStr;
         QObject *obj = OBJECT_PTR(node);
-        QVariant value = obj->property(name.toLatin1());
-        if (!value.isValid()) {
-            if (name == QLatin1String("class")) {
-                QString className = QString::fromLatin1(obj->metaObject()->className());
-                if (className.contains(QLatin1Char(':')))
-                    className.replace(QLatin1Char(':'), QLatin1Char('-'));
-                cache[name] = className;
-                return className;
-            } else if (name == QLatin1String("style")) {
-                QWidget *w = qobject_cast<QWidget *>(obj);
-                QStyleSheetStyle *proxy = w ? qt_styleSheet(w->style()) : nullptr;
-                if (proxy) {
-                    QString styleName = QString::fromLatin1(proxy->baseStyle()->metaObject()->className());
-                    cache[name] = styleName;
-                    return styleName;
+        const int propertyIndex = obj->metaObject()->indexOfProperty(name.toLatin1());
+        if (propertyIndex == -1) {
+            value = obj->property(name.toLatin1()); // might be a dynamic property
+            if (!value.isValid()) {
+                if (name == u"class"_qs) {
+                    QString className = QString::fromLatin1(obj->metaObject()->className());
+                    if (className.contains(QLatin1Char(':')))
+                        className.replace(QLatin1Char(':'), QLatin1Char('-'));
+                    valueStr = className;
+                } else if (name == u"style"_qs) {
+                    QWidget *w = qobject_cast<QWidget *>(obj);
+                    QStyleSheetStyle *proxy = w ? qt_styleSheet(w->style()) : nullptr;
+                    if (proxy)
+                        valueStr = QString::fromLatin1(proxy->baseStyle()->metaObject()->className());
                 }
             }
+        } else {
+            const QMetaProperty property = obj->metaObject()->property(propertyIndex);
+            value = property.read(obj);
+            // support Qt 5 selector syntax, which required the integer enum value
+            if (property.isEnumType()) {
+                bool isNumber;
+                aSelector.value.toInt(&isNumber);
+                if (isNumber)
+                    value.convert(QMetaType::fromType<int>());
+            }
+        }
+        if (value.isValid()) {
+            valueStr = (value.userType() == QMetaType::QStringList
+                        || value.userType() == QMetaType::QVariantList)
+                        ? value.toStringList().join(QLatin1Char(' '))
+                        : value.toString();
         }
-        QString valueStr = (value.userType() == QMetaType::QStringList
-            || value.userType() == QMetaType::QVariantList)
-            ? value.toStringList().join(QLatin1Char(' '))
-            : value.toString();
         cache[name] = valueStr;
         return valueStr;
     }