Make QStyle::proxy() always return the leaf proxy

For example:

  fusion -> proxy1 -> proxy2

Now returns proxy2.

Fixes: QTBUG-85556
Pick-to: 6.0 5.15
Change-Id: I2a60329f948b59ef7d0752d273bee3854a200547
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/widgets/styles/qstyle.cpp b/src/widgets/styles/qstyle.cpp
index c839afd639..8aa423c224 100644
--- a/src/widgets/styles/qstyle.cpp
+++ b/src/widgets/styles/qstyle.cpp
@@ -2430,17 +2430,19 @@ int QStyle::combinedLayoutSpacing(QSizePolicy::ControlTypes controls1,
 const QStyle * QStyle::proxy() const
 {
     Q_D(const QStyle);
-    return d->proxyStyle;
+    return d->proxyStyle == this ? this : d->proxyStyle->proxy();
 }
 
 /* \internal
 
     This function sets the base style that style calls will be
-    redirected to. Note that ownership is not transferred.
+    redirected to. Note that ownership is not transferred. \a style
+    must be a valid pointer (not nullptr).
 */
 void QStyle::setProxy(QStyle *style)
 {
     Q_D(QStyle);
+    Q_ASSERT(style);
     d->proxyStyle = style;
 }