Make QQuickStyleSelector::select() more robust

While debugging QTBUG-59026, I found out that QLocale::name() is empty
with the "C" locale. Because the empty locale name was used as a selector
in QQuickStyleSelector, it ended up registering QML types using URLs
that contained a double slash (empty locale selector matched):

    QtQuick/Controls.2/Material//RadioButton.qml

At the same time, the QML engine imported implicitly internal QML types
constructing the URLs directly based on the location on the file system
without a double slash:

    QtQuick/Controls.2/Material/RadioIndicator.qml

As a result, the same QML module ended up having types registered from
two different URLs, which is not allowed.

This change simply prevents both problems. First of all, if the locale
name is empty for any reason, it won't be added anymore to the list of
selectors. Furthermore, the final selected URL is normalized to avoid
redundant dashes.

Task-number: QTBUG-59026
Change-Id: I19b890451aaddfe4277bb6b26bc3c1394a75a704
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

1 files changed, 4 insertions, 2 deletions

diff --git a/src/quickcontrols2/qquickstyleselector.cpp b/src/quickcontrols2/qquickstyleselector.cpp
index e20096c9..6d04c190 100644
--- a/src/quickcontrols2/qquickstyleselector.cpp
+++ b/src/quickcontrols2/qquickstyleselector.cpp
@@ -69,7 +69,9 @@ static QStringList allSelectors(const QString &style = QString())
 {
     static const QStringList platformSelectors = QFileSelectorPrivate::platformSelectors();
     QStringList selectors = platformSelectors;
-    selectors += QLocale().name();
+    const QString locale = QLocale().name();
+    if (!locale.isEmpty())
+        selectors += locale;
     if (!style.isEmpty())
         selectors.prepend(style);
     return selectors;
@@ -161,7 +163,7 @@ QString QQuickStyleSelector::select(const QString &fileName) const
     } else if (url.isLocalFile()) {
         url = QUrl::fromLocalFile(d->select(url.toLocalFile()));
     }
-    return url.toString();
+    return url.toString(QUrl::NormalizePathSegments);
 }
 
 QT_END_NAMESPACE