Add file selector for custom styles when using run-time style selection

Previously this was only available for QQuickStylePlugin-based styles.

This patch makes it available for qmldir-based styles when using
run-time style selection.

The existing documentation doesn't differentiate between built-in
styles and custom styles:

"Qt Quick Controls extends the built-in selectors with the name
(lowercase) of the style that an application is running with."

So this is a bug fix.

Change-Id: Ib2ed56ad8398db49d192db6a6023d776caaa4457
Fixes: QTBUG-99117
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
(cherry picked from commit fdd62a5b81)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/quickcontrols2/qtquickcontrols2plugin.cpp

@@ -34,6 +34,7 @@
 **
 ******************************************************************************/
 
+#include <QtCore/private/qfileselector_p.h>
 #include <QtCore/qloggingcategory.h>
 #include <QtQml/qqmlengine.h>
 #include <QtQml/qqmlextensionplugin.h>
@@ -145,6 +146,9 @@ void QtQuickControls2Plugin::registerTypes(const char *uri)
         << " uri \"" << qtQuickControlsUri << "\" moduleMajor " << importMajor
         << " import " << registeredStyleUri << " importMajor " << importMajor;
     qmlRegisterModuleImport(qtQuickControlsUri, QQmlModuleImportModuleAny, registeredStyleUri.toUtf8().constData(), importMajor);
+
+    if (customStyle)
+        QFileSelectorPrivate::addStatics(QStringList() << styleName);
 }
 
 void QtQuickControls2Plugin::unregisterTypes()

tests/auto/quickcontrols2/styleimports/data/+FileSystemStyle/CustomComponent.qml

@@ -0,0 +1,5 @@
+import QtQuick
+
+Item {
+    objectName: "+FileSystemStyle/CustomComponent.qml"
+}

tests/auto/quickcontrols2/styleimports/data/CustomComponent.qml

@@ -0,0 +1,5 @@
+import QtQuick
+
+Item {
+    objectName: "CustomComponent.qml"
+}

tests/auto/quickcontrols2/styleimports/data/customStyleSelector.qml

@@ -0,0 +1,64 @@
+/****************************************************************************
+**
+** 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.
+**
+** $QT_BEGIN_LICENSE:BSD$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see https://www.qt.io/terms-conditions. For further
+** information use the contact form at https://www.qt.io/contact-us.
+**
+** BSD License Usage
+** Alternatively, you may use this file under the terms of the BSD license
+** as follows:
+**
+** "Redistribution and use in source and binary forms, with or without
+** modification, are permitted provided that the following conditions are
+** met:
+**   * Redistributions of source code must retain the above copyright
+**     notice, this list of conditions and the following disclaimer.
+**   * Redistributions in binary form must reproduce the above copyright
+**     notice, this list of conditions and the following disclaimer in
+**     the documentation and/or other materials provided with the
+**     distribution.
+**   * Neither the name of The Qt Company Ltd nor the names of its
+**     contributors may be used to endorse or promote products derived
+**     from this software without specific prior written permission.
+**
+**
+** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+** A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+** OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+** SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+** LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+** DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+** THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+** (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+** OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE."
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+import QtQuick
+import QtQuick.Controls
+
+ApplicationWindow {
+    title: "Test Application Window"
+    width: 400
+    height: 400
+
+    property alias customComponent: customComponent
+
+    CustomComponent {
+        id: customComponent
+    }
+}

tests/auto/quickcontrols2/styleimports/tst_styleimports.cpp

@@ -62,6 +62,7 @@ private slots:
     void select();
 
     void platformSelectors();
+    void customStyleSelector();
 
     void fallbackStyleShouldNotOverwriteTheme_data();
     void fallbackStyleShouldNotOverwriteTheme();
@@ -180,6 +181,7 @@ void tst_StyleImports::select()
     }
 }
 
+// Tests that the various platforms are available as selectors.
 void tst_StyleImports::platformSelectors()
 {
     QQuickStyle::setStyle(QLatin1String("PlatformStyle"));
@@ -205,6 +207,27 @@ void tst_StyleImports::platformSelectors()
 #endif
 }
 
+// Tests that a file selector is added for custom styles.
+// Note that this is different to the regular QML import mechanism
+// that results in e.g. FileSystemStyle/Button.qml being found;
+// it allows non-template (Controls), custom user types to be
+// picked up via selectors.
+void tst_StyleImports::customStyleSelector()
+{
+    QQuickStyle::setStyle(QLatin1String("FileSystemStyle"));
+
+    QQmlApplicationEngine engine;
+    engine.addImportPath(dataDirectory() + QLatin1String("/styles"));
+    engine.load(testFileUrl("customStyleSelector.qml"));
+    QVERIFY(!engine.rootObjects().isEmpty());
+    QQuickWindow *window = qobject_cast<QQuickWindow*>(engine.rootObjects().first());
+    QVERIFY(window);
+
+    QObject *customComponent = window->property("customComponent").value<QObject*>();
+    QVERIFY(customComponent);
+    QCOMPARE(customComponent->objectName(), "+FileSystemStyle/CustomComponent.qml");
+}
+
 void tst_StyleImports::fallbackStyleShouldNotOverwriteTheme_data()
 {
     QTest::addColumn<QString>("style");