Add support for FileChooser flatpak portal

Adds support for FileChooser Flatpak portal. To support them we just do
specific DBus calls, which are then caught and forwarded by xdg-desktop-
portal daemon/service. This is needed for Qt applications running in
sandbox.

[ChangeLog][Platform Specific Changes][Linux] Added support for flatpak
portals. Flatpak is a software utility for software deployment and
package management. It provides a sandbox environment in which users
can run applications in isolation from the rest of the system. To
communicate with the system flatpak uses portals, which are designed to
be a bridge between sandboxed applications and desktop/system running on
user's computer. Flatpak runs this service (called xdg-desktop-portal)
automatically. It exports the portals via DBus and they are visible by
default to all applications running under Flatpak.

Change-Id: I4de1402434ba7cbcc805eab51c30f84f8ba0c5c5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

8 files changed, 883 insertions, 0 deletions

diff --git a/src/plugins/platformthemes/flatpak/flatpak.json b/src/plugins/platformthemes/flatpak/flatpak.json
new file mode 100644
index 0000000000..71f834fd08
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/flatpak.json
@@ -0,0 +1,3 @@
+{
+    "Keys": [ "flatpak" ]
+}
diff --git a/src/plugins/platformthemes/flatpak/flatpak.pro b/src/plugins/platformthemes/flatpak/flatpak.pro
new file mode 100644
index 0000000000..1e5dbb7a6c
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/flatpak.pro
@@ -0,0 +1,17 @@
+TARGET = qflatpak
+
+PLUGIN_TYPE = platformthemes
+PLUGIN_EXTENDS = -
+PLUGIN_CLASS_NAME = QFlatpakThemePlugin
+load(qt_plugin)
+
+QT += core-private dbus gui-private theme_support-private
+
+HEADERS += \
+        qflatpaktheme.h \
+        qflatpakfiledialog_p.h
+
+SOURCES += \
+        main.cpp \
+        qflatpaktheme.cpp \
+        qflatpakfiledialog.cpp
diff --git a/src/plugins/platformthemes/flatpak/main.cpp b/src/plugins/platformthemes/flatpak/main.cpp
new file mode 100644
index 0000000000..7888eed8b2
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/main.cpp
@@ -0,0 +1,65 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Red Hat, Inc
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <qpa/qplatformthemeplugin.h>
+#include "qflatpaktheme.h"
+
+QT_BEGIN_NAMESPACE
+
+class QFlatpakThemePlugin : public QPlatformThemePlugin
+{
+   Q_OBJECT
+   Q_PLUGIN_METADATA(IID QPlatformThemeFactoryInterface_iid FILE "flatpak.json")
+
+public:
+    QPlatformTheme *create(const QString &key, const QStringList &params) override;
+};
+
+QPlatformTheme *QFlatpakThemePlugin::create(const QString &key, const QStringList &params)
+{
+    Q_UNUSED(params);
+    if (!key.compare(QLatin1String("flatpak"), Qt::CaseInsensitive))
+        return new QFlatpakTheme;
+
+    return nullptr;
+}
+
+QT_END_NAMESPACE
+
+#include "main.moc"
diff --git a/src/plugins/platformthemes/flatpak/qflatpakfiledialog.cpp b/src/plugins/platformthemes/flatpak/qflatpakfiledialog.cpp
new file mode 100644
index 0000000000..0dadb9a2f1
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/qflatpakfiledialog.cpp
@@ -0,0 +1,347 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Red Hat, Inc
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qflatpakfiledialog_p.h"
+
+#include <QtCore/qeventloop.h>
+
+#include <QtDBus/QtDBus>
+#include <QDBusConnection>
+#include <QDBusMessage>
+#include <QDBusPendingCall>
+#include <QDBusPendingCallWatcher>
+#include <QDBusPendingReply>
+
+#include <QMetaType>
+#include <QMimeType>
+#include <QMimeDatabase>
+#include <QWindow>
+
+QT_BEGIN_NAMESPACE
+
+QDBusArgument &operator <<(QDBusArgument &arg, const QFlatpakFileDialog::FilterCondition &filterCondition)
+{
+    arg.beginStructure();
+    arg << filterCondition.type << filterCondition.pattern;
+    arg.endStructure();
+    return arg;
+}
+
+const QDBusArgument &operator >>(const QDBusArgument &arg, QFlatpakFileDialog::FilterCondition &filterCondition)
+{
+    uint type;
+    QString filterPattern;
+    arg.beginStructure();
+    arg >> type >> filterPattern;
+    filterCondition.type = (QFlatpakFileDialog::ConditionType)type;
+    filterCondition.pattern = filterPattern;
+    arg.endStructure();
+
+    return arg;
+}
+
+QDBusArgument &operator <<(QDBusArgument &arg, const QFlatpakFileDialog::Filter filter)
+{
+    arg.beginStructure();
+    arg << filter.name << filter.filterConditions;
+    arg.endStructure();
+    return arg;
+}
+
+const QDBusArgument &operator >>(const QDBusArgument &arg, QFlatpakFileDialog::Filter &filter)
+{
+    QString name;
+    QFlatpakFileDialog::FilterConditionList filterConditions;
+    arg.beginStructure();
+    arg >> name >> filterConditions;
+    filter.name = name;
+    filter.filterConditions = filterConditions;
+    arg.endStructure();
+
+    return arg;
+}
+
+class QFlatpakFileDialogPrivate
+{
+public:
+    WId winId = 0;
+    bool modal = false;
+    bool multipleFiles = false;
+    bool saveFile = false;
+    QString acceptLabel;
+    QString directory;
+    QString title;
+    QStringList nameFilters;
+    QStringList mimeTypesFilters;
+    QStringList selectedFiles;
+};
+
+QFlatpakFileDialog::QFlatpakFileDialog()
+    : QPlatformFileDialogHelper()
+    , d_ptr(new QFlatpakFileDialogPrivate)
+{
+}
+
+QFlatpakFileDialog::~QFlatpakFileDialog()
+{
+}
+
+void QFlatpakFileDialog::initializeDialog()
+{
+    Q_D(QFlatpakFileDialog);
+
+    if (options()->fileMode() == QFileDialogOptions::ExistingFiles)
+        d->multipleFiles = true;
+
+    if (options()->isLabelExplicitlySet(QFileDialogOptions::Accept))
+        d->acceptLabel = options()->labelText(QFileDialogOptions::Accept);
+
+    if (!options()->windowTitle().isEmpty())
+        d->title = options()->windowTitle();
+
+    if (options()->acceptMode() == QFileDialogOptions::AcceptSave)
+        d->saveFile = true;
+
+    if (!options()->nameFilters().isEmpty())
+        d->nameFilters = options()->nameFilters();
+
+    if (!options()->mimeTypeFilters().isEmpty())
+        d->mimeTypesFilters = options()->mimeTypeFilters();
+
+    setDirectory(options()->initialDirectory());
+}
+
+bool QFlatpakFileDialog::defaultNameFilterDisables() const
+{
+    return false;
+}
+
+void QFlatpakFileDialog::setDirectory(const QUrl &directory)
+{
+    Q_D(QFlatpakFileDialog);
+
+    d->directory = directory.path();
+}
+
+QUrl QFlatpakFileDialog::directory() const
+{
+    Q_D(const QFlatpakFileDialog);
+
+    return d->directory;
+}
+
+void QFlatpakFileDialog::selectFile(const QUrl &filename)
+{
+    Q_D(QFlatpakFileDialog);
+
+    d->selectedFiles << filename.path();
+}
+
+QList<QUrl> QFlatpakFileDialog::selectedFiles() const
+{
+    Q_D(const QFlatpakFileDialog);
+
+    QList<QUrl> files;
+    for (const QString &file : d->selectedFiles) {
+        files << QUrl(file);
+    }
+    return files;
+}
+
+void QFlatpakFileDialog::setFilter()
+{
+    // TODO
+}
+
+void QFlatpakFileDialog::selectNameFilter(const QString &filter)
+{
+    Q_UNUSED(filter);
+    // TODO
+}
+
+QString QFlatpakFileDialog::selectedNameFilter() const
+{
+    // TODO
+    return QString();
+}
+
+void QFlatpakFileDialog::exec()
+{
+    Q_D(const QFlatpakFileDialog);
+
+    QDBusMessage message = QDBusMessage::createMethodCall(QLatin1String("org.freedesktop.portal.Desktop"),
+                                                          QLatin1String("/org/freedesktop/portal/desktop"),
+                                                          QLatin1String("org.freedesktop.portal.FileChooser"),
+                                                          d->saveFile ? QLatin1String("SaveFile") : QLatin1String("OpenFile"));
+    QString parentWindowId = QLatin1String("x11:") + QString::number(d->winId);
+
+    QVariantMap options;
+    if (!d->acceptLabel.isEmpty())
+        options.insert(QLatin1String("accept_label"), d->acceptLabel);
+
+    options.insert(QLatin1String("modal"), d->modal);
+    options.insert(QLatin1String("multiple"), d->multipleFiles);
+
+    if (d->saveFile) {
+        if (!d->directory.isEmpty())
+            options.insert(QLatin1String("current_folder"), d->directory.toLatin1());
+
+        if (!d->selectedFiles.isEmpty())
+            options.insert(QLatin1String("current_file"), d->selectedFiles.first().toLatin1());
+    }
+
+    // Insert filters
+    qDBusRegisterMetaType<FilterCondition>();
+    qDBusRegisterMetaType<FilterConditionList>();
+    qDBusRegisterMetaType<Filter>();
+    qDBusRegisterMetaType<FilterList>();
+
+    FilterList filterList;
+
+    if (!d->mimeTypesFilters.isEmpty()) {
+        for (const QString &mimeTypefilter : d->mimeTypesFilters) {
+            QMimeDatabase mimeDatabase;
+            QMimeType mimeType = mimeDatabase.mimeTypeForName(mimeTypefilter);
+
+            // Creates e.g. (1, "image/png")
+            FilterCondition filterCondition;
+            filterCondition.type = MimeType;
+            filterCondition.pattern = mimeTypefilter;
+
+            // Creates e.g. [((1, "image/png"))]
+            FilterConditionList filterConditions;
+            filterConditions << filterCondition;
+
+            // Creates e.g. [("Images", [((1, "image/png"))])]
+            Filter filter;
+            filter.name = mimeType.comment();
+            filter.filterConditions = filterConditions;
+
+            filterList << filter;
+        }
+    } else if (!d->nameFilters.isEmpty()) {
+        for (const QString &filter : d->nameFilters) {
+            // Do parsing:
+            // Supported format is ("Images (*.png *.jpg)")
+            QRegularExpression regexp(QPlatformFileDialogHelper::filterRegExp);
+            QRegularExpressionMatch match = regexp.match(filter);
+            if (match.hasMatch()) {
+                QString userVisibleName = match.captured(0);
+                QStringList filterStrings = match.captured(1).split(QLatin1String(" "));
+
+                FilterConditionList filterConditions;
+                for (const QString &filterString : filterStrings) {
+                    FilterCondition filterCondition;
+                    filterCondition.type = GlobalPattern;
+                    filterCondition.pattern = filterString;
+                    filterConditions << filterCondition;
+                }
+
+                Filter filter;
+                filter.name = userVisibleName;
+                filter.filterConditions = filterConditions;
+
+                filterList << filter;
+            }
+        }
+    }
+
+    if (!filterList.isEmpty())
+        options.insert(QLatin1String("filters"), QVariant::fromValue(filterList));
+
+    // TODO choices a(ssa(ss)s)
+    // List of serialized combo boxes to add to the file chooser.
+
+    message << parentWindowId << d->title << options;
+
+    QDBusPendingCall pendingCall = QDBusConnection::sessionBus().asyncCall(message);
+    QDBusPendingCallWatcher *watcher = new QDBusPendingCallWatcher(pendingCall);
+    connect(watcher, &QDBusPendingCallWatcher::finished, this, [this] (QDBusPendingCallWatcher *watcher) {
+        QDBusPendingReply<QDBusObjectPath> reply = *watcher;
+        if (reply.isError()) {
+            Q_EMIT reject();
+        } else {
+            QDBusConnection::sessionBus().connect(nullptr,
+                                                  reply.value().path(),
+                                                  QLatin1String("org.freedesktop.portal.Request"),
+                                                  QLatin1String("Response"),
+                                                  this,
+                                                  SLOT(gotResponse(uint,QVariantMap)));
+        }
+    });
+
+    // HACK we have to avoid returning until we emit that the dialog was accepted or rejected
+    QEventLoop loop;
+    loop.connect(this, SIGNAL(accept()), SLOT(quit()));
+    loop.connect(this, SIGNAL(reject()), SLOT(quit()));
+    loop.exec();
+}
+
+void QFlatpakFileDialog::hide()
+{
+}
+
+bool QFlatpakFileDialog::show(Qt::WindowFlags windowFlags, Qt::WindowModality windowModality, QWindow *parent)
+{
+    Q_D(QFlatpakFileDialog);
+    Q_UNUSED(windowFlags);
+
+    initializeDialog();
+
+    d->modal = windowModality != Qt::NonModal;
+    d->winId = parent ? parent->winId() : 0;
+
+    return true;
+}
+
+void QFlatpakFileDialog::gotResponse(uint response, const QVariantMap &results)
+{
+    Q_D(QFlatpakFileDialog);
+
+    if (!response) {
+        if (results.contains(QLatin1String("uris")))
+            d->selectedFiles = results.value(QLatin1String("uris")).toStringList();
+
+        Q_EMIT accept();
+    } else {
+        Q_EMIT reject();
+    }
+}
+
+QT_END_NAMESPACE
diff --git a/src/plugins/platformthemes/flatpak/qflatpakfiledialog_p.h b/src/plugins/platformthemes/flatpak/qflatpakfiledialog_p.h
new file mode 100644
index 0000000000..256f35f7a6
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/qflatpakfiledialog_p.h
@@ -0,0 +1,105 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 Red Hat, Inc
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+#ifndef QFLATPAKFILEDIALOG_P_H
+#define QFLATPAKFILEDIALOG_P_H
+
+#include <qpa/qplatformdialoghelper.h>
+#include <QVector>
+
+QT_BEGIN_NAMESPACE
+
+class QFlatpakFileDialogPrivate;
+
+class QFlatpakFileDialog : public QPlatformFileDialogHelper
+{
+    Q_OBJECT
+    Q_DECLARE_PRIVATE(QFlatpakFileDialog)
+public:
+    enum ConditionType {
+        GlobalPattern = 0,
+        MimeType = 1
+    };
+    // Filters a(sa(us))
+    // Example: [('Images', [(0, '*.ico'), (1, 'image/png')]), ('Text', [(0, '*.txt')])]
+    struct FilterCondition {
+        ConditionType type;
+        QString pattern; // E.g. '*ico' or 'image/png'
+    };
+    typedef QVector<FilterCondition> FilterConditionList;
+
+    struct Filter {
+        QString name; // E.g. 'Images' or 'Text
+        FilterConditionList filterConditions;; // E.g. [(0, '*.ico'), (1, 'image/png')] or [(0, '*.txt')]
+    };
+    typedef QVector<Filter> FilterList;
+
+    QFlatpakFileDialog();
+    ~QFlatpakFileDialog();
+
+    bool defaultNameFilterDisables() const override;
+    QUrl directory() const override;
+    void setDirectory(const QUrl &directory) override;
+    void selectFile(const QUrl &filename) override;
+    QList<QUrl> selectedFiles() const override;
+    void setFilter() override;
+    void selectNameFilter(const QString &filter) override;
+    QString selectedNameFilter() const override;
+
+    void exec() override;
+    bool show(Qt::WindowFlags windowFlags, Qt::WindowModality windowModality, QWindow *parent) override;
+    void hide() override;
+
+private Q_SLOTS:
+    void gotResponse(uint response, const QVariantMap &results);
+
+private:
+    void initializeDialog();
+
+    QScopedPointer<QFlatpakFileDialogPrivate> d_ptr;
+};
+
+QT_END_NAMESPACE
+
+Q_DECLARE_METATYPE(QFlatpakFileDialog::FilterCondition);
+Q_DECLARE_METATYPE(QFlatpakFileDialog::FilterConditionList);
+Q_DECLARE_METATYPE(QFlatpakFileDialog::Filter);
+Q_DECLARE_METATYPE(QFlatpakFileDialog::FilterList);
+
+#endif // QFLATPAKFILEDIALOG_P_H
+
diff --git a/src/plugins/platformthemes/flatpak/qflatpaktheme.cpp b/src/plugins/platformthemes/flatpak/qflatpaktheme.cpp
new file mode 100644
index 0000000000..04abd707e1
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/qflatpaktheme.cpp
@@ -0,0 +1,254 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include "qflatpaktheme.h"
+#include "qflatpakfiledialog_p.h"
+
+#include <private/qguiapplication_p.h>
+#include <qpa/qplatformtheme_p.h>
+#include <qpa/qplatformthemefactory_p.h>
+#include <qpa/qplatformintegration.h>
+
+QT_BEGIN_NAMESPACE
+
+class QFlatpakThemePrivate : public QPlatformThemePrivate
+{
+public:
+    QFlatpakThemePrivate()
+        : QPlatformThemePrivate()
+    { }
+
+    ~QFlatpakThemePrivate()
+    {
+        delete baseTheme;
+    }
+
+    QPlatformTheme *baseTheme;
+};
+
+QFlatpakTheme::QFlatpakTheme()
+    : d_ptr(new QFlatpakThemePrivate)
+{
+    Q_D(QFlatpakTheme);
+
+    QStringList themeNames;
+    themeNames += QGuiApplicationPrivate::platform_integration->themeNames();
+    // 1) Look for a theme plugin.
+    for (const QString &themeName : qAsConst(themeNames)) {
+        d->baseTheme = QPlatformThemeFactory::create(themeName, nullptr);
+        if (d->baseTheme)
+            break;
+    }
+
+    // 2) If no theme plugin was found ask the platform integration to
+    // create a theme
+    if (!d->baseTheme) {
+        for (const QString &themeName : qAsConst(themeNames)) {
+            d->baseTheme = QGuiApplicationPrivate::platform_integration->createPlatformTheme(themeName);
+            if (d->baseTheme)
+                break;
+        }
+        // No error message; not having a theme plugin is allowed.
+    }
+
+    // 3) Fall back on the built-in "null" platform theme.
+    if (!d->baseTheme)
+        d->baseTheme = new QPlatformTheme;
+}
+
+QPlatformMenuItem* QFlatpakTheme::createPlatformMenuItem() const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->createPlatformMenuItem();
+
+    return QPlatformTheme::createPlatformMenuItem();
+}
+
+QPlatformMenu* QFlatpakTheme::createPlatformMenu() const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->createPlatformMenu();
+
+    return QPlatformTheme::createPlatformMenu();
+}
+
+QPlatformMenuBar* QFlatpakTheme::createPlatformMenuBar() const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->createPlatformMenuBar();
+
+    return QFlatpakTheme::createPlatformMenuBar();
+}
+
+void QFlatpakTheme::showPlatformMenuBar()
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->showPlatformMenuBar();
+
+    return QFlatpakTheme::showPlatformMenuBar();
+}
+
+bool QFlatpakTheme::usePlatformNativeDialog(DialogType type) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (type == FileDialog)
+        return true;
+
+    if (d->baseTheme)
+        return d->baseTheme->usePlatformNativeDialog(type);
+
+    return QFlatpakTheme::usePlatformNativeDialog(type);
+}
+
+QPlatformDialogHelper* QFlatpakTheme::createPlatformDialogHelper(DialogType type) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (type == FileDialog)
+        return new QFlatpakFileDialog;
+
+    if (d->baseTheme)
+        return d->baseTheme->createPlatformDialogHelper(type);
+
+    return QFlatpakTheme::createPlatformDialogHelper(type);
+}
+
+#ifndef QT_NO_SYSTEMTRAYICON
+QPlatformSystemTrayIcon* QFlatpakTheme::createPlatformSystemTrayIcon() const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->createPlatformSystemTrayIcon();
+
+    return QPlatformTheme::createPlatformSystemTrayIcon();
+}
+#endif
+
+const QPalette *QFlatpakTheme::palette(Palette type) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->palette(type);
+
+    return QPlatformTheme::palette(type);
+}
+
+const QFont* QFlatpakTheme::font(Font type) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->font(type);
+
+    return QPlatformTheme::font(type);
+}
+
+QVariant QFlatpakTheme::themeHint(ThemeHint hint) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->themeHint(hint);
+
+    return QPlatformTheme::themeHint(hint);
+}
+
+QPixmap QFlatpakTheme::standardPixmap(StandardPixmap sp, const QSizeF &size) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->standardPixmap(sp, size);
+
+    return QPlatformTheme::standardPixmap(sp, size);
+}
+
+QIcon QFlatpakTheme::fileIcon(const QFileInfo &fileInfo,
+                              QPlatformTheme::IconOptions iconOptions) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->fileIcon(fileInfo, iconOptions);
+
+    return QPlatformTheme::fileIcon(fileInfo, iconOptions);
+}
+
+QIconEngine * QFlatpakTheme::createIconEngine(const QString &iconName) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->createIconEngine(iconName);
+
+    return QPlatformTheme::createIconEngine(iconName);
+}
+
+QList<QKeySequence> QFlatpakTheme::keyBindings(QKeySequence::StandardKey key) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->keyBindings(key);
+
+    return QPlatformTheme::keyBindings(key);
+}
+
+QString QFlatpakTheme::standardButtonText(int button) const
+{
+    Q_D(const QFlatpakTheme);
+
+    if (d->baseTheme)
+        return d->baseTheme->standardButtonText(button);
+
+    return QPlatformTheme::standardButtonText(button);
+}
+
+QT_END_NAMESPACE
diff --git a/src/plugins/platformthemes/flatpak/qflatpaktheme.h b/src/plugins/platformthemes/flatpak/qflatpaktheme.h
new file mode 100644
index 0000000000..fcaac5b673
--- /dev/null
+++ b/src/plugins/platformthemes/flatpak/qflatpaktheme.h
@@ -0,0 +1,90 @@
+/****************************************************************************
+**
+** Copyright (C) 2017 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the plugins of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** 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.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 3 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL3 included in the
+** packaging of this file. Please review the following information to
+** ensure the GNU Lesser General Public License version 3 requirements
+** will be met: https://www.gnu.org/licenses/lgpl-3.0.html.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 2.0 or (at your option) the GNU General
+** Public license version 3 or any later version approved by the KDE Free
+** Qt Foundation. The licenses are as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL2 and LICENSE.GPL3
+** included in the packaging of this file. Please review the following
+** information to ensure the GNU General Public License requirements will
+** be met: https://www.gnu.org/licenses/gpl-2.0.html and
+** https://www.gnu.org/licenses/gpl-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QFLATPAKTHEME_H
+#define QFLATPAKTHEME_H
+
+#include <qpa/qplatformtheme.h>
+
+QT_BEGIN_NAMESPACE
+
+class QFlatpakThemePrivate;
+
+class QFlatpakTheme : public QPlatformTheme
+{
+    Q_DECLARE_PRIVATE(QFlatpakTheme)
+public:
+    QFlatpakTheme();
+
+    QPlatformMenuItem *createPlatformMenuItem() const override;
+    QPlatformMenu *createPlatformMenu() const override;
+    QPlatformMenuBar *createPlatformMenuBar() const override;
+    void showPlatformMenuBar() override;
+
+    bool usePlatformNativeDialog(DialogType type) const override;
+    QPlatformDialogHelper *createPlatformDialogHelper(DialogType type) const override;
+
+#ifndef QT_NO_SYSTEMTRAYICON
+    QPlatformSystemTrayIcon *createPlatformSystemTrayIcon() const override;
+#endif
+
+    const QPalette *palette(Palette type = SystemPalette) const override;
+
+    const QFont *font(Font type = SystemFont) const override;
+
+    QVariant themeHint(ThemeHint hint) const override;
+
+    QPixmap standardPixmap(StandardPixmap sp, const QSizeF &size) const override;
+    QIcon fileIcon(const QFileInfo &fileInfo,
+                   QPlatformTheme::IconOptions iconOptions = 0) const;
+
+    QIconEngine *createIconEngine(const QString &iconName) const override;
+
+    QList<QKeySequence> keyBindings(QKeySequence::StandardKey key) const override;
+
+    QString standardButtonText(int button) const override;
+
+private:
+    QScopedPointer<QFlatpakThemePrivate> d_ptr;
+    Q_DISABLE_COPY(QFlatpakTheme)
+};
+
+QT_END_NAMESPACE
+
+#endif // QFLATPAKTHEME_H
diff --git a/src/plugins/platformthemes/platformthemes.pro b/src/plugins/platformthemes/platformthemes.pro
index 0e2812bed3..ebf92ba9d5 100644
--- a/src/plugins/platformthemes/platformthemes.pro
+++ b/src/plugins/platformthemes/platformthemes.pro
@@ -1,4 +1,6 @@
 TEMPLATE = subdirs
 QT_FOR_CONFIG += widgets-private
 
+qtConfig(dbus): SUBDIRS += flatpak
+
 qtHaveModule(widgets):qtConfig(gtk3): SUBDIRS += gtk3