client: Allow QWaylandInputContext to accept composed key combinations

At the moment, we are forcing user to choose to either compose or use
the text-input channel. This patch brings some of the QComposeInputContext
functionality in order to let applications understand dead key
combinations like they are supposed to.

Having it in QWaylandInputContext rather than in QWaylandInputDevice
should solve the problems 3aedd01271dc4f4a13103d632df224971ab2b6df had
with 57c4af2b18c0fb1d266b245a107fa6cb876b9d9e, because we are doing it
in the input context rather than before. This way, if the user is
overriding the input method (e.g. by setting QT_IM_MODULE), all the key
strokes will still be properly forwarded to the module to use.

This in turn allows us to solve https://bugs.kde.org/show_bug.cgi?id=411729
and https://bugs.kde.org/show_bug.cgi?id=405388 since we don't need to
choose anymore between physical and virual keyboards anymore.

Pick-to: 5.15
Change-Id: I8601f5d7ae21edf4b3a1191fa75877286e505588
Reviewed-by: David Edmundson <davidedmundson@kde.org>

5 files changed, 119 insertions, 10 deletions

diff --git a/src/client/qwaylanddisplay_p.h b/src/client/qwaylanddisplay_p.h
index 6443cff2b..91715a144 100644
--- a/src/client/qwaylanddisplay_p.h
+++ b/src/client/qwaylanddisplay_p.h
@@ -178,8 +178,6 @@ public:
     QWaylandHardwareIntegration *hardwareIntegration() const { return mHardwareIntegration.data(); }
     QWaylandXdgOutputManagerV1 *xdgOutputManager() const { return mXdgOutputManager.data(); }
 
-    bool usingInputContextFromCompositor() const { return mUsingInputContextFromCompositor; }
-
     struct RegistryGlobal {
         uint32_t id;
         QString interface;
@@ -299,7 +297,6 @@ private:
     QReadWriteLock m_frameQueueLock;
 
     bool mClientSideInputContextRequested = !QPlatformInputContextFactory::requested().isNull();
-    bool mUsingInputContextFromCompositor = false;
 
     void registry_global(uint32_t id, const QString &interface, uint32_t version) override;
     void registry_global_remove(uint32_t id) override;
diff --git a/src/client/qwaylandinputcontext.cpp b/src/client/qwaylandinputcontext.cpp
index 6c586960e..16e03ea17 100644
--- a/src/client/qwaylandinputcontext.cpp
+++ b/src/client/qwaylandinputcontext.cpp
@@ -408,6 +408,8 @@ bool QWaylandInputContext::isValid() const
 void QWaylandInputContext::reset()
 {
     qCDebug(qLcQpaInputMethods) << Q_FUNC_INFO;
+    if (m_composeState)
+        xkb_compose_state_reset(m_composeState);
 
     QPlatformInputContext::reset();
 
@@ -528,9 +530,14 @@ Qt::LayoutDirection QWaylandInputContext::inputDirection() const
     return textInput()->inputDirection();
 }
 
-void QWaylandInputContext::setFocusObject(QObject *)
+void QWaylandInputContext::setFocusObject(QObject *object)
 {
     qCDebug(qLcQpaInputMethods) << Q_FUNC_INFO;
+#if QT_CONFIG(xkbcommon)
+    m_focusObject = object;
+#else
+    Q_UNUSED(object);
+#endif
 
     if (!textInput())
         return;
@@ -563,6 +570,92 @@ QWaylandTextInput *QWaylandInputContext::textInput() const
     return mDisplay->defaultInputDevice()->textInput();
 }
 
+#if QT_CONFIG(xkbcommon)
+
+void QWaylandInputContext::ensureInitialized()
+{
+    if (m_initialized)
+        return;
+
+    if (!m_XkbContext) {
+        qCWarning(qLcQpaInputMethods) << "error: xkb context has not been set on" << metaObject()->className();
+        return;
+    }
+
+    m_initialized = true;
+    const char *locale = setlocale(LC_CTYPE, "");
+    if (!locale)
+        locale = setlocale(LC_CTYPE, nullptr);
+    qCDebug(qLcQpaInputMethods) << "detected locale (LC_CTYPE):" << locale;
+
+    m_composeTable = xkb_compose_table_new_from_locale(m_XkbContext, locale, XKB_COMPOSE_COMPILE_NO_FLAGS);
+    if (m_composeTable)
+        m_composeState = xkb_compose_state_new(m_composeTable, XKB_COMPOSE_STATE_NO_FLAGS);
+
+    if (!m_composeTable) {
+        qCWarning(qLcQpaInputMethods, "failed to create compose table");
+        return;
+    }
+    if (!m_composeState) {
+        qCWarning(qLcQpaInputMethods, "failed to create compose state");
+        return;
+    }
+}
+
+bool QWaylandInputContext::filterEvent(const QEvent *event)
+{
+    auto keyEvent = static_cast<const QKeyEvent *>(event);
+    if (keyEvent->type() != QEvent::KeyPress)
+        return false;
+
+    if (!inputMethodAccepted())
+        return false;
+
+    // lazy initialization - we don't want to do this on an app startup
+    ensureInitialized();
+
+    if (!m_composeTable || !m_composeState)
+        return false;
+
+    xkb_compose_state_feed(m_composeState, keyEvent->nativeVirtualKey());
+
+    switch (xkb_compose_state_get_status(m_composeState)) {
+    case XKB_COMPOSE_COMPOSING:
+        return true;
+    case XKB_COMPOSE_CANCELLED:
+        reset();
+        return false;
+    case XKB_COMPOSE_COMPOSED:
+    {
+        const int size = xkb_compose_state_get_utf8(m_composeState, nullptr, 0);
+        QVarLengthArray<char, 32> buffer(size + 1);
+        xkb_compose_state_get_utf8(m_composeState, buffer.data(), buffer.size());
+        QString composedText = QString::fromUtf8(buffer.constData());
+
+        QInputMethodEvent event;
+        event.setCommitString(composedText);
+
+        if (!m_focusObject && qApp)
+            m_focusObject = qApp->focusObject();
+
+        if (m_focusObject)
+            QCoreApplication::sendEvent(m_focusObject, &event);
+        else
+            qCWarning(qLcQpaInputMethods, "no focus object");
+
+        reset();
+        return true;
+    }
+    case XKB_COMPOSE_NOTHING:
+        return false;
+    default:
+        Q_UNREACHABLE();
+        return false;
+    }
+}
+
+#endif
+
 }
 
 QT_END_NAMESPACE
diff --git a/src/client/qwaylandinputcontext_p.h b/src/client/qwaylandinputcontext_p.h
index df91856c4..912c68ad4 100644
--- a/src/client/qwaylandinputcontext_p.h
+++ b/src/client/qwaylandinputcontext_p.h
@@ -62,6 +62,10 @@
 
 #include <QtWaylandClient/private/qwayland-text-input-unstable-v2.h>
 #include <qwaylandinputmethodeventbuilder_p.h>
+#include <qtwaylandclientglobal_p.h>
+#if QT_CONFIG(xkbcommon)
+#include <xkbcommon/xkbcommon-compose.h>
+#endif
 
 struct wl_callback;
 struct wl_callback_listener;
@@ -156,11 +160,28 @@ public:
 
     void setFocusObject(QObject *object) override;
 
+#if QT_CONFIG(xkbcommon)
+    bool filterEvent(const QEvent *event) override;
+
+    // This invokable is called from QXkbCommon::setXkbContext().
+    Q_INVOKABLE void setXkbContext(struct xkb_context *context) { m_XkbContext = context; }
+#endif
+
 private:
     QWaylandTextInput *textInput() const;
 
     QWaylandDisplay *mDisplay = nullptr;
     QPointer<QWindow> mCurrentWindow;
+
+#if QT_CONFIG(xkbcommon)
+    void ensureInitialized();
+
+    bool m_initialized = false;
+    QObject *m_focusObject = nullptr;
+    xkb_compose_table *m_composeTable = nullptr;
+    xkb_compose_state *m_composeState = nullptr;
+    struct xkb_context *m_XkbContext = nullptr;
+#endif
 };
 
 }
diff --git a/src/client/qwaylandinputdevice.cpp b/src/client/qwaylandinputdevice.cpp
index 420194733..4a046a134 100644
--- a/src/client/qwaylandinputdevice.cpp
+++ b/src/client/qwaylandinputdevice.cpp
@@ -1213,7 +1213,7 @@ void QWaylandInputDevice::Keyboard::handleKey(ulong timestamp, QEvent::Type type
     QPlatformInputContext *inputContext = QGuiApplicationPrivate::platformIntegration()->inputContext();
     bool filtered = false;
 
-    if (inputContext && !mParent->mQDisplay->usingInputContextFromCompositor()) {
+    if (inputContext) {
         QKeyEvent event(type, key, modifiers, nativeScanCode, nativeVirtualKey,
                         nativeModifiers, text, autorepeat, count);
         event.setTimestamp(timestamp);
diff --git a/src/client/qwaylandintegration.cpp b/src/client/qwaylandintegration.cpp
index 7e7567aa8..09de7dddd 100644
--- a/src/client/qwaylandintegration.cpp
+++ b/src/client/qwaylandintegration.cpp
@@ -500,13 +500,11 @@ void QWaylandIntegration::reconfigureInputContext()
 
 #if QT_CONFIG(xkbcommon)
     QXkbCommon::setXkbContext(mInputContext.data(), mDisplay->xkbContext());
+    if (QWaylandInputContext* waylandInput = qobject_cast<QWaylandInputContext*>(mInputContext.get())) {
+        waylandInput->setXkbContext(mDisplay->xkbContext());
+    }
 #endif
 
-    // Even if compositor-side input context handling has been requested, we fallback to
-    // client-side handling if compositor does not provide the text-input extension. This
-    // is why we need to check here which input context actually is being used.
-    mDisplay->mUsingInputContextFromCompositor = qobject_cast<QWaylandInputContext *>(mInputContext.data());
-
     qCDebug(lcQpaWayland) << "using input method:" << inputContext()->metaObject()->className();
 }