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, 0 deletions

diff --git a/src/plugins/platforms/xcb/qxcbintegration.cpp b/src/plugins/platforms/xcb/qxcbintegration.cpp
index ed9e87a036..a70c7db923 100644
--- a/src/plugins/platforms/xcb/qxcbintegration.cpp
+++ b/src/plugins/platforms/xcb/qxcbintegration.cpp
@@ -357,6 +357,8 @@ void QXcbIntegration::initialize()
     m_inputContext.reset(QPlatformInputContextFactory::create(icStr));
     if (!m_inputContext && icStr != defaultInputContext && icStr != QLatin1String("none"))
         m_inputContext.reset(QPlatformInputContextFactory::create(defaultInputContext));
+
+    defaultConnection()->keyboard()->initialize();
 }
 
 void QXcbIntegration::moveToScreen(QWindow *window, int screen)