ui/gtk3: Fix Emojier on Plasma Wayland

Using Wayland popup window requires to share the display with
input-method protocol but merging ibus-ui-gtk3 and ibus-extension-gtk3
will causes several leaks and now IBus keeps to separate
ibus-extension-gtk3 and the Emoji category dialog from ibus-ui-gtk3
at the moment. I'd like to fix several Emojier issues later.

This way needs to remember the previous input context path before
the Emojier is launched since the popup window takes the input focus
in the Wayland desktop session but the Wayland input-method version 1
always remakes the input context by the focus change so the exact
match of input context paths is deleted at the moment.
Also Qt applications commit the preedit text with focus-out events
so Emojier clears the preedit prefix "e" before Emojier is launched.

BUG=#2408

ui/gtk3/panelbinding.vala

@@ -502,9 +502,18 @@ class PanelBinding : IBus.PanelService {
             return true;
         string selected_string = m_emojier.get_selected_string();
         string prev_context_path = m_emojier.get_input_context_path();
-        if (selected_string != null &&
-            prev_context_path != "" &&
-            prev_context_path == m_current_context_path) {
+        if (selected_string != null && prev_context_path != "") {
+            if (prev_context_path != m_current_context_path) {
+                if (m_is_wayland) {
+                    // Using Wayland input-method protocol in Plasma Wayland
+                    // always allocates new input contexts with focus changes.
+                    debug("Prev input context path %s, now %s",
+                          prev_context_path,
+                          m_current_context_path);
+                } else {
+                    return false;
+                }
+            }
             IBus.Text text = new IBus.Text.from_string(selected_string);
             commit_text_update_favorites(text, false);
             m_emojier.reset();
@@ -776,18 +785,36 @@ class PanelBinding : IBus.PanelService {
 
     private void show_preedit_and_candidate(bool show_candidate) {
         uint cursor_pos = 0;
+        IBus.Text text;
+        bool visible = true;
+
         if (!show_candidate)
             cursor_pos = m_preedit.get_engine_preedit_cursor_pos();
+        /* Showing Emojier in Wayland takes the input focus
+         * and the focus change causes the preedit commit in Qt applications
+         * likes kwrite.
+         * so need to clear the preedit text before showing Emojier.
+         *
+         * Use m_preedit.get_text() because
+         * m_wayland_lookup_table_is_visible will be true after
+         * show_emoji_lookup_table() is called below.
+         */
+        if (show_candidate && m_is_wayland && m_preedit.get_text() == "") {
+            if (m_emojier == null)
+                return;
+            visible = false;
+            text = new IBus.Text.from_static_string("");
+        } else {
+            text = m_preedit.get_engine_preedit_text();
+        }
         update_preedit_text_received(
-                m_preedit.get_engine_preedit_text(),
+                text,
                 cursor_pos,
-                true);
+                visible);
         if (!show_candidate) {
             hide_emoji_lookup_table();
             return;
         }
-        if (m_emojier == null)
-            return;
         /* Wayland gives the focus on Emojir which is a GTK popup window
          * and move the focus fom the current input context to Emojier.
          * This forwards the lookup table to gnome-shell's lookup table
@@ -923,6 +950,17 @@ class PanelBinding : IBus.PanelService {
 
     public override void hide_preedit_text() {
         m_preedit.hide_engine_preedit_text();
+        /* Space key to launch Emojier category popup causes a hide-preedit-text
+         * signal by ibus_engine_simple_update_preedit_text().
+         * On the other hand, the Emoji preedit "e" should be hidden
+         * in Plasam Wayland before Qt applications commit the preedit
+         * with the focus-out event.
+         * So avoid the duplicated show_preedit_and_candidate() here.
+         * Emojier should hide the preedit by itself instead of the callback
+         * of each engine.
+         */
+        if (m_is_wayland && m_preedit.get_text() == "")
+            return;
         show_preedit_and_candidate(false);
     }