QGuiApplication: use translation-based layout direction unless explicitly set

The stored layout direction used to get changed during initialization
to what was auto-detected based on the translation. Changing the
translation then overwrote that stored value, even if an explicit call
to setLayoutDirection was made by the application.

Calling QGuiApplication::setLayoutDirection(Auto) has so far been a
no-op.

Change this logic so that the stored layout direction continues to be
LayoutDirectionAuto also if it's set based on auto-detection, and only
overwrite it when explicitly called with a non-Auto value. This way,
applications can set a layout direction that stays unchanged even when
translators are installed.

Add test coverage that uses a QTranslator.

In practice, this is not a change of behavior, unless applications called
setLayoutDirection(Auto) (which is no longer a no-op), or called
setLayoutDirection() and then installed a translator and expected the
translator's layout direction to come into effect in spite of the explicit
setting.

[ChangeLog][Gui][QGuiApplication] Calling setLayoutDirection with a non-
auto value now disables the auto-detection based on installed
translators. Applications that explicitly set a layout direction and also
want translators installed afterwards to take effect should reset the
layout direction to Auto, which is now no longer a no-op.

Fixes: QTBUG-100632
Change-Id: I1fdcebd43a9b1b468ff95bf15f53f441bb214e08
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit 4cca8ee527bfa94947f897d4d9b91aa8eb63d9c3)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

1 files changed, 58 insertions, 2 deletions

diff --git a/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp b/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
index 5eab76898b..e3b4bd296f 100644
--- a/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
+++ b/tests/auto/gui/kernel/qguiapplication/tst_qguiapplication.cpp
@@ -1158,8 +1158,8 @@ void tst_QGuiApplication::layoutDirection()
 {
     qRegisterMetaType<Qt::LayoutDirection>();
 
-    Qt::LayoutDirection oldDirection = QGuiApplication::layoutDirection();
-    Qt::LayoutDirection newDirection = oldDirection == Qt::LeftToRight ? Qt::RightToLeft : Qt::LeftToRight;
+    const Qt::LayoutDirection oldDirection = QGuiApplication::layoutDirection();
+    const Qt::LayoutDirection newDirection = oldDirection == Qt::LeftToRight ? Qt::RightToLeft : Qt::LeftToRight;
 
     QGuiApplication::setLayoutDirection(newDirection);
     QCOMPARE(QGuiApplication::layoutDirection(), newDirection);
@@ -1177,8 +1177,64 @@ void tst_QGuiApplication::layoutDirection()
     QGuiApplication::setLayoutDirection(oldDirection);
     QCOMPARE(QGuiApplication::layoutDirection(), oldDirection);
     QCOMPARE(signalSpy.count(), 1);
+
+    // with QGuiApplication instantiated, install a translator that gives us control
+    class LayoutDirectionTranslator : public QTranslator
+    {
+    public:
+        LayoutDirectionTranslator(Qt::LayoutDirection direction)
+        : direction(direction)
+        {}
+
+        bool isEmpty() const override { return false; }
+        QString translate(const char *context, const char *sourceText, const char *disambiguation, int n) const override
+        {
+            if (QByteArrayView(sourceText) == "QT_LAYOUT_DIRECTION")
+                return direction == Qt::LeftToRight ? QLatin1String("LTR") : QLatin1String("RTL");
+            return QTranslator::translate(context, sourceText, disambiguation, n);
+        }
+
+        const Qt::LayoutDirection direction;
+    };
+
+    int layoutDirectionChangedCount = 0;
+    // reset to auto-detection, should be back to oldDirection now
+    QGuiApplication::setLayoutDirection(Qt::LayoutDirectionAuto);
+    QCOMPARE(QGuiApplication::layoutDirection(), oldDirection);
+    signalSpy.clear();
+    {
+        // this translator doesn't change the direction
+        LayoutDirectionTranslator translator(oldDirection);
+        QGuiApplication::installTranslator(&translator);
+        QCOMPARE(QGuiApplication::layoutDirection(), translator.direction);
+        QCOMPARE(signalSpy.count(), layoutDirectionChangedCount);
+    }
+    QCOMPARE(signalSpy.count(), layoutDirectionChangedCount); // ltrTranslator removed, no change
+
+    // install a new translator that changes the direction
+    {
+        LayoutDirectionTranslator translator(newDirection);
+        QGuiApplication::installTranslator(&translator);
+        QCOMPARE(QGuiApplication::layoutDirection(), translator.direction);
+        QCOMPARE(signalSpy.count(), ++layoutDirectionChangedCount);
+    }
+    // rtlTranslator removed
+    QCOMPARE(signalSpy.count(), ++layoutDirectionChangedCount);
+
+    // override translation
+    QGuiApplication::setLayoutDirection(newDirection);
+    QCOMPARE(signalSpy.count(), ++layoutDirectionChangedCount);
+    {
+        // this translator will be ignored
+        LayoutDirectionTranslator translator(oldDirection);
+        QGuiApplication::installTranslator(&translator);
+        QCOMPARE(QGuiApplication::layoutDirection(), newDirection);
+        QCOMPARE(signalSpy.count(), layoutDirectionChangedCount);
+    }
+    QCOMPARE(signalSpy.count(), layoutDirectionChangedCount);
 }
 
+
 void tst_QGuiApplication::globalShareContext()
 {
 #ifndef QT_NO_OPENGL