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>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontextmain.cpp b/src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontextmain.cpp
index 6b33df65b9..d062d4fd6a 100644
--- a/src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontextmain.cpp
+++ b/src/plugins/platforminputcontexts/compose/qcomposeplatforminputcontextmain.cpp
@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2019 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the plugins of the Qt Toolkit.
@@ -61,7 +61,7 @@ QComposeInputContext *QComposePlatformInputContextPlugin::create(const QString &
     if (system.compare(system, QLatin1String("compose"), Qt::CaseInsensitive) == 0
             || system.compare(system, QLatin1String("xim"), Qt::CaseInsensitive) == 0)
         return new QComposeInputContext;
-    return 0;
+    return nullptr;
 }
 
 QT_END_NAMESPACE