Fix QStatusBar::removeWidget to hide the right widget

`QStatusBar::removeWidget` was hiding the wrong widget (the next one),
since the `removeAt` call changed the item that the `item` variable
is referencing.

This fixes a regression in Qt 6.3.0 (7166a82844500238a4dad91857384479c7).

Change-Id: I9977b47e6208f8d451ff1037bcb9f4e8414cb431
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Thorbjørn Lindeijer <bjorn@lindeijer.nl>
(cherry picked from commit 3e7226f10702828eaaf2fa939efc2ac476e8a2b4)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/widgets/qstatusbar.cpp

@@ -355,19 +355,10 @@ void QStatusBar::removeWidget(QWidget *widget)
         return;
 
     Q_D(QStatusBar);
-    bool found = false;
+    if (d->items.removeIf([widget](const auto &item) { return item.widget == widget; })) {
-    for (int i = 0; i < d->items.size(); ++i) {
+        widget->hide();
-        const auto &item = d->items.at(i);
-        if (item.widget == widget) {
-            d->items.removeAt(i);
-            item.widget->hide();
-            found = true;
-            break;
-        }
-    }
-
-    if (found)
         reformat();
+    }
 #if defined(QT_DEBUG)
     else
         qDebug("QStatusBar::removeWidget(): Widget not found.");

tests/auto/widgets/widgets/qstatusbar/tst_qstatusbar.cpp

@@ -23,6 +23,7 @@ private slots:
     void tempMessage();
     void insertWidget();
     void insertPermanentWidget();
+    void removeWidget();
     void setSizeGripEnabled();
     void task194017_hiddenWidget();
     void QTBUG4334_hiddenOnMaximizedWindow();
@@ -104,6 +105,49 @@ void tst_QStatusBar::insertPermanentWidget()
     QCOMPARE(sb.insertPermanentWidget(1, new QLabel("foo")), 6);
 }
 
+void tst_QStatusBar::removeWidget()
+{
+    QStatusBar sb;
+    std::vector<std::unique_ptr<QLabel>> widgets;
+    std::vector<bool> states;
+    for (int i = 0; i < 10; ++i) {
+        const QString text = i > 5 ? QString("p_%1").arg(i) : QString::number(i);
+        widgets.push_back(std::make_unique<QLabel>(text));
+        states.push_back(true);
+    }
+
+    for (auto &&widget : widgets) {
+        if (widget->text().startsWith("p_"))
+            sb.addPermanentWidget(widget.get());
+        else
+            sb.addWidget(widget.get());
+    }
+    sb.show();
+    QVERIFY(QTest::qWaitForWindowExposed(&sb));
+
+    auto checkStates = [&]{
+        for (size_t index = 0; index < std::size(widgets); ++index) {
+            if (widgets.at(index)->isVisible() != states.at(index)) {
+                qCritical("Mismatch for widget at index %zu\n"
+                          "\tActual  : %s\n"
+                          "\tExpected: %s",
+                          index, widgets.at(index)->isVisible() ? "true" : "false",
+                          states.at(index) ? "true" : "false");
+                return false;
+            }
+        }
+        return true;
+    };
+
+    QVERIFY(checkStates());
+    // remove every widget except the first to trigger unstable reference
+    for (size_t i = 2; i < std::size(widgets); ++i) {
+        sb.removeWidget(widgets[i].get());
+        states[i] = false;
+        QVERIFY2(checkStates(), qPrintable(QString("Failure at index %1").arg(i)));
+    }
+}
+
 void tst_QStatusBar::setSizeGripEnabled()
 {
     if (QGuiApplication::platformName().startsWith(QLatin1String("wayland"), Qt::CaseInsensitive))