QQuickStyleSelector: fix built-in file selectors

While selecting style files, the standard built-in platform and local
file selectors ("+linux", "+macos", "+windows"...) must be prefixed
with the standard file selector indicator ("+"). Previously the style
selector would not pick up platform-specific style files unless they
were supplied without the prefix.

[ChangeLog][Controls][Styles] Fixed the style selection mechanism so
that now it is possible to organize platform and locale-specific files
into sub-directories, such as "+linux", "+macos", and "+windows".

Change-Id: Ia44b6f14fd0247943486fd27609147827bda9666
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/quickcontrols2/qquickstyleselector.cpp

@@ -65,13 +65,21 @@ static QString ensureSlash(const QString &path)
     return path + QLatin1Char('/');
 }
 
+static QStringList prefixedPlatformSelectors(const QChar &prefix)
+{
+    QStringList selectors = QFileSelectorPrivate::platformSelectors();
+    for (int i = 0; i < selectors.count(); ++i)
+        selectors[i].prepend(prefix);
+    return selectors;
+}
+
 static QStringList allSelectors(const QString &style = QString())
 {
-    static const QStringList platformSelectors = QFileSelectorPrivate::platformSelectors();
+    static const QStringList platformSelectors = prefixedPlatformSelectors(QLatin1Char('+'));
     QStringList selectors = platformSelectors;
     const QString locale = QLocale().name();
     if (!locale.isEmpty())
-        selectors += locale;
+        selectors += QLatin1Char('+') + locale;
     if (!style.isEmpty())
         selectors.prepend(style);
     return selectors;

tests/auto/qquickstyleselector/data/PlatformStyle/+linux/Button.qml

@@ -0,0 +1,2 @@
+import QtQuick.Templates 2.1 as T
+T.Button { }

tests/auto/qquickstyleselector/data/PlatformStyle/+macos/Button.qml

@@ -0,0 +1,2 @@
+import QtQuick.Templates 2.1 as T
+T.Button { }

tests/auto/qquickstyleselector/data/PlatformStyle/+windows/Button.qml

@@ -0,0 +1,2 @@
+import QtQuick.Templates 2.1 as T
+T.Button { }

tests/auto/qquickstyleselector/data/PlatformStyle/Button.qml

@@ -0,0 +1,2 @@
+import QtQuick.Templates 2.1 as T
+T.Button { }

tests/auto/qquickstyleselector/tst_qquickstyleselector.cpp

@@ -49,6 +49,8 @@ private slots:
 
     void select_data();
     void select();
+
+    void platformSelectors();
 };
 
 void tst_QQuickStyleSelector::initTestCase()
@@ -139,6 +141,24 @@ void tst_QQuickStyleSelector::select()
     QCOMPARE(selector.select(file), expected);
 }
 
+void tst_QQuickStyleSelector::platformSelectors()
+{
+    QQuickStyle::setStyle(QDir(dataDirectory()).filePath("PlatformStyle"));
+
+    QQuickStyleSelector selector;
+    selector.setBaseUrl(dataDirectoryUrl());
+
+#if defined(Q_OS_LINUX)
+    QCOMPARE(selector.select("Button.qml"), testFileUrl("PlatformStyle/+linux/Button.qml").toString());
+#elif defined(Q_OS_MACOS)
+    QCOMPARE(selector.select("Button.qml"), testFileUrl("PlatformStyle/+macos/Button.qml").toString());
+#elif defined(Q_OS_WIN)
+    QCOMPARE(selector.select("Button.qml"), testFileUrl("PlatformStyle/+windows/Button.qml").toString());
+#else
+    QCOMPARE(selector.select("Button.qml"), testFileUrl("PlatformStyle/Button.qml").toString());
+#endif
+}
+
 QTEST_MAIN(tst_QQuickStyleSelector)
 
 #include "tst_qquickstyleselector.moc"