Repolish child widgets when parent style sheet changes

If a child widget that is affected by the parent's style sheet is
polished (because it's been shown explicitly, for instance by a layout),
then it must be repolished when the parent's style sheet changes, even
if the parent itself has not been polished yet.

Since the style sheet is set on the parent widget, we must repolish the
parent (which will repolish the entire widget tree), not just the
individual children and grand children.

Fixes: QTBUG-76945
Task-number: QTBUG-39427
Task-number: QTBUG-18958
Change-Id: I7bca9ee1badc07202fa05dc97f440f4ca6c9517d
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Andy Shaw <andy.shaw@qt.io>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/widgets/kernel/qwidget.cpp b/src/widgets/kernel/qwidget.cpp
index a5ad101201..95d38c4882 100644
--- a/src/widgets/kernel/qwidget.cpp
+++ b/src/widgets/kernel/qwidget.cpp
@@ -2575,7 +2575,16 @@ void QWidget::setStyleSheet(const QString& styleSheet)
     }
 
     if (proxy) { // style sheet update
-        if (d->polished)
+        bool repolish = d->polished;
+        if (!repolish) {
+            const auto childWidgets = findChildren<QWidget*>();
+            for (auto child : childWidgets) {
+                repolish = child->d_func()->polished;
+                if (repolish)
+                    break;
+            }
+        }
+        if (repolish)
             proxy->repolish(this);
         return;
     }