xcb: Correctly update primary screen status with RandR 1.5

This amends d8f37d94e537aaab4fa960b80aacabe79bcc14c4 .

Fixes: QTBUG-99605
Pick-to: 6.3
Done-with: Liang Qi <liang.qi@qt.io>
Change-Id: Ia4cf67d6ebeed36596c0342302aa0b4af01769bc
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/plugins/platforms/xcb/qxcbconnection_screens.cpp

@@ -191,7 +191,7 @@ void QXcbConnection::updateScreens(const xcb_randr_notify_event_t *event)
             }
         }
 
-        qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
+        qCDebug(lcQpaScreen) << "updateScreens: primary output is" << qAsConst(m_screens).first()->name();
     }
 }
 
@@ -379,7 +379,7 @@ void QXcbConnection::initializeScreens(bool initialized)
         }
 
         if (!m_screens.isEmpty())
-            qCDebug(lcQpaScreen) << "primary output is" << qAsConst(m_screens).first()->name();
+            qCDebug(lcQpaScreen) << "initializeScreens: primary output is" << qAsConst(m_screens).first()->name();
     }
 }
 
@@ -534,11 +534,6 @@ void QXcbConnection::initializeScreensFromMonitor(xcb_screen_iterator_t *it, int
 
         siblings << screen;
 
-        if (primaryScreenNumber() == xcbScreenNumber) {
-            primaryScreen = screen;
-            primaryScreen->setPrimary(true);
-        }
-
         xcb_randr_monitor_info_next(&monitor_iter);
     }
 

src/plugins/platforms/xcb/qxcbscreen.cpp

@@ -705,9 +705,7 @@ void QXcbScreen::setMonitor(xcb_randr_monitor_info_t *monitorInfo, xcb_timestamp
 
     QByteArray ba = connection()->atomName(monitorInfo->name);
     m_outputName = getName(monitorInfo);
-
+    m_primary = monitorInfo->primary;
-    if (monitorInfo->primary)
-        m_primary = true;
 
     m_cursor = new QXcbCursor(connection(), this);
 }

tests/manual/qscreen_xrandr/tst_qscreen_xrandr.cpp

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2020 The Qt Company Ltd.
+** Copyright (C) 2022 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the test suite of the Qt Toolkit.
@@ -42,6 +42,7 @@ private slots:
     void xrandr_15_merge_and_unmerge();
     void xrandr_15_scale();
     void xrandr_15_off_and_on();
+    void xrandr_15_primary();
 
 private:
     void xrandr_process(const QStringList &arguments = {});
@@ -199,6 +200,38 @@ void tst_QScreen_Xrandr::xrandr_15_off_and_on()
     }
 }
 
+void tst_QScreen_Xrandr::xrandr_15_primary()
+{
+    QList<QScreen *> screens = QGuiApplication::screens();
+    int ss = screens.size();
+    if (ss < 2)
+        QSKIP("This test requires at least two screens.");
+
+    QStringList names;
+    for (QScreen *s : screens)
+        names << s->name();
+
+    qDebug() << "All screens: " << names;
+    QScreen *ps = qGuiApp->primaryScreen();
+    qDebug() << "Current primary screen: " << ps;
+
+    QStringList args;
+    for (QString name : names) {
+        qDebug() << "Trying to set primary screen:" << name;
+        args.clear();
+        args << "--output" << name << "--primary";
+        xrandr_process(args);
+        QTest::qWait(500);
+
+        QScreen *ps = qGuiApp->primaryScreen();
+        qDebug() << "Current primary screen: " << ps;
+        if (ps) {
+            qDebug() << "primary screen name: " << ps->name();
+            QVERIFY(ps->name() == name);
+        }
+    }
+}
+
 void tst_QScreen_Xrandr::xrandr_process(const QStringList &args)
 {
     QString prog = "xrandr";