platforminputcontexts: use libxkbcommon compose key API

Our implementation of compose table parser was added on Mar, 2013.
libxkbcommon added APIs for the same thing in Oct, 2014 (ver: 0.5.0).
After removing RHEL 6.6 from the list of supported platforms we were
able to move the minimal required libxkbcommon version to 0.5.0. Now
we can use the xkbcommon-compose APIs on all supported platforms.

With this patch we can drop nearly 1000 lines of maintenance burden.
This patch fixes user reported issues with our implementation.

Known issues:

- Testing revealed that xkbcommon-compose does not support non-utf8 locales,
and that is by design - https://github.com/xkbcommon/libxkbcommon/issues/76
Our implementation did work for those locales too, but it is unclear
if anyone actually uses non-utf8 locales. It is a corner case (work-arounds
existing) and likely a configuration error on the users' system.

- Looking at the release notes for versions above 0.6.1, only one issue
that stands out. Compose input does not work on system with tr_TR.UTF-8
locale, fixed in 0.7.1. Compose input works fine when using e.g. en_US.UTF-8
locale with Turkish keyboard layout.

Note:

With Qt 5.13 we have removed Ubuntu 16.04 and openSUSE 42.3 from CI:

Ubuntu 16.04  - 0.5.0
openSUSE 42.3 - 0.6.1

CI for Qt 5.13 has:

Ubuntu 18.04  - 0.8.0
RHEL-7.4      - 0.7.1
openSUSE 15.0 - 0.8.1

Currently the minimal required libxkbcommon version in src/gui/configure.json
is set to 0.5.0, but we could bump it to 0.7.1 to avoid known issues from above,
but that is a decision for a separate patch.

[ChangeLog][plugins][platforminputcontexts] Now using libxkbcommon-compose
APIs for compose key input, instead of Qt's own implementation.

Fixes: QTBUG-42181
Fixes: QTBUG-53663
Fixes: QTBUG-48657
Change-Id: I79aafe2bc601293844066e7e5f5eddd3719c6bba
Reviewed-by: Giulio Camuffo <giulio.camuffo@kdab.com>
Reviewed-by: Johan Helsing <johan.helsing@qt.io>

3 files changed, 72 insertions, 0 deletions

diff --git a/tests/auto/other/other.pro b/tests/auto/other/other.pro
index a720860288..378750472d 100644
--- a/tests/auto/other/other.pro
+++ b/tests/auto/other/other.pro
@@ -67,3 +67,8 @@ winrt|!qtHaveModule(gui)|!qtConfig(accessibility): SUBDIRS -= qaccessibility
 
 android: SUBDIRS += \
     android
+
+qtConfig(xkbcommon): {
+    SUBDIRS += \
+        xkbkeyboard
+}
diff --git a/tests/auto/other/xkbkeyboard/tst_xkbkeyboard.cpp b/tests/auto/other/xkbkeyboard/tst_xkbkeyboard.cpp
new file mode 100644
index 0000000000..65364eddf4
--- /dev/null
+++ b/tests/auto/other/xkbkeyboard/tst_xkbkeyboard.cpp
@@ -0,0 +1,60 @@
+/****************************************************************************
+**
+** Copyright (C) 2019 The Qt Company Ltd.
+** Contact: https://www.qt.io/licensing/
+**
+** This file is part of the test suite of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:GPL-EXCEPT$
+** 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 General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3 as published by the Free Software
+** Foundation with exceptions as appearing in the file LICENSE.GPL3-EXCEPT
+** 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-3.0.html.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#include <QtCore>
+#include <QtGui>
+#include <QtTest>
+
+#include <qpa/qplatforminputcontextfactory_p.h>
+#include <qpa/qplatforminputcontext.h>
+
+class tst_XkbKeyboard : public QObject
+{
+    Q_OBJECT
+private slots:
+    void verifyComposeInputContextInterface();
+};
+
+void tst_XkbKeyboard::verifyComposeInputContextInterface()
+{
+    QPlatformInputContext *inputContext = QPlatformInputContextFactory::create(QStringLiteral("compose"));
+    QVERIFY(inputContext);
+
+    const char *const inputContextClassName = "QComposeInputContext";
+    const char *const normalizedSignature = "setXkbContext(xkb_context*)";
+
+    QVERIFY(inputContext->objectName() == QLatin1String(inputContextClassName));
+
+    int methodIndex = inputContext->metaObject()->indexOfMethod(normalizedSignature);
+    QMetaMethod method = inputContext->metaObject()->method(methodIndex);
+    Q_ASSERT(method.isValid());
+}
+
+QTEST_MAIN(tst_XkbKeyboard)
+#include "tst_xkbkeyboard.moc"
+
diff --git a/tests/auto/other/xkbkeyboard/xkbkeyboard.pro b/tests/auto/other/xkbkeyboard/xkbkeyboard.pro
new file mode 100644
index 0000000000..17396ee475
--- /dev/null
+++ b/tests/auto/other/xkbkeyboard/xkbkeyboard.pro
@@ -0,0 +1,7 @@
+CONFIG += testcase
+TARGET = tst_xkbkeyboard
+
+SOURCES += tst_xkbkeyboard.cpp
+
+QT = core-private gui-private testlib
+