QStyle: add name() to return the name of the style

Currently there is no way to get the name of the current style to e.g.
create a QProxyStyle for a specific widget only.
Therefore add QStyle::name() so QProxyStyle(const QString &) can be
called without hard-coding the style name.
Remove an unused doc snippet as drive-by.

Fixes: QTBUG-8004
Change-Id: I466c5e870a5392b238365bdc930f6a2ecee50cdb
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/widgets/doc/snippets/code/src_gui_qproxystyle.cpp

@@ -48,22 +48,6 @@
 **
 ****************************************************************************/
 
-//! [0]
-class MyProxyStyle : public QProxyStyle
-{
-public:
-
-    int styleHint(StyleHint hint, const QStyleOption *option = nullptr,
-                  const QWidget *widget = nullptr, QStyleHintReturn *returnData = nullptr) const override
-    {
-        if (hint == QStyle::SH_UnderlineShortcut)
-            return 1;
-        return QProxyStyle::styleHint(hint, option, widget, returnData);
-    }
-};
-
-//! [0]
-
 //! [1]
 #include "textedit.h"
 #include <QApplication>
@@ -93,3 +77,11 @@ int main(int argc, char **argv)
     //...
 }
 //! [1]
+
+//! [2]
+...
+auto proxy = new MyProxyStyle(QApplication::style()->name());
+proxy->setParent(widget);   // take ownership to avoid memleak
+widget->setStyle(proxy);
+...
+//! [2]

src/widgets/styles/qproxystyle.cpp

@@ -72,6 +72,13 @@ QT_BEGIN_NAMESPACE
     or system controlled styles. It would not work on a Mac, for
     example, where menus are handled by the operating system.
 
+    When a proxy style should be set on a specific widget only, you have
+    to make sure to not set the proxy on the global application style which
+    is returned by QWidget::style(). You have to create a separate custom style
+    for the widget similar to:
+
+    \snippet code/src_gui_qproxystyle.cpp 2
+
     \sa QStyle
 */
 

src/widgets/styles/qstyle.cpp

@@ -421,6 +421,30 @@ QStyle::~QStyle()
 {
 }
 
+/*!
+    Returns the name of the style.
+
+    This value can be used to create a style with QStyleFactory::create().
+
+    \sa QStyleFactory::create()
+    \since 6.1
+*/
+QString QStyle::name() const
+{
+    Q_D(const QStyle);
+    return d->name;
+}
+
+/*!
+    \internal
+    Set the style name
+*/
+void QStyle::setName(const QString &name)
+{
+    Q_D(QStyle);
+    d->name = name;
+}
+
 /*!
     Initializes the appearance of the given \a widget.
 

src/widgets/styles/qstyle.h

@@ -73,6 +73,8 @@ public:
     QStyle();
     virtual ~QStyle();
 
+    QString name() const;
+
     virtual void polish(QWidget *widget);
     virtual void unpolish(QWidget *widget);
 
@@ -854,6 +856,9 @@ public:
 
     const QStyle * proxy() const;
 
+private:
+    void setName(const QString &name);
+
 private:
     Q_DISABLE_COPY(QStyle)
     friend class QWidget;
@@ -861,6 +866,7 @@ private:
     friend class QApplication;
     friend class QProxyStyle;
     friend class QProxyStylePrivate;
+    friend class QStyleFactory;
     void setProxy(QStyle *style);
 };
 

src/widgets/styles/qstyle_p.h

@@ -72,6 +72,7 @@ public:
 
     mutable int layoutSpacingIndex;
     QStyle *proxyStyle;
+    QString name;
 };
 
 inline QImage styleCacheImage(const QSize &size)

src/widgets/styles/qstylefactory.cpp

@@ -109,8 +109,10 @@ QStyle *QStyleFactory::create(const QString& key)
     { } // Keep these here - they make the #ifdefery above work
     if (!ret)
         ret = qLoadPlugin<QStyle, QStylePlugin>(loader(), style);
-    if (ret)
+    if (ret) {
         ret->setObjectName(style);
+        ret->setName(style);
+    }
     return ret;
 }