[mutter/wip/carlosg/no-null-preedit-repeat] wayland: Avoid repeated NULL preedit string updates

[Carlos Garnacho <carlosg src gnome org>]

commit 8b0f5746fe5585b154af8ebe2898f880c7635333
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sat Apr 30 13:51:28 2022 +0200

    wayland: Avoid repeated NULL preedit string updates
    
    Simply signal preedit string changes from/to NULL once, in order
    to avoid unwanted activity in the client side. We do still need to
    send the preedit once each .done event, if there is one, in order
    to behave according to the protocol when it matters the most.

 src/wayland/meta-wayland-text-input.c | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)
---
diff --git a/src/wayland/meta-wayland-text-input.c b/src/wayland/meta-wayland-text-input.c
index 17e0b683e7..cf40f02183 100644
--- a/src/wayland/meta-wayland-text-input.c
+++ b/src/wayland/meta-wayland-text-input.c
@@ -79,6 +79,7 @@ struct _MetaWaylandTextInput
     char *string;
     uint32_t cursor;
     uint32_t anchor;
+    gboolean changed;
   } preedit;
 
   guint done_idle_id;
@@ -136,10 +137,15 @@ clutter_input_focus_send_done (ClutterInputFocus *focus)
 
   wl_resource_for_each (resource, &text_input->focus_resource_list)
     {
-      zwp_text_input_v3_send_preedit_string (resource,
-                                             text_input->preedit.string,
-                                             text_input->preedit.cursor,
-                                             text_input->preedit.anchor);
+      if (text_input->preedit.string || text_input->preedit.changed)
+        {
+          zwp_text_input_v3_send_preedit_string (resource,
+                                                 text_input->preedit.string,
+                                                 text_input->preedit.cursor,
+                                                 text_input->preedit.anchor);
+          text_input->preedit.changed = FALSE;
+        }
+
       zwp_text_input_v3_send_done (resource,
                                    lookup_serial (text_input, resource));
     }
@@ -260,6 +266,7 @@ meta_wayland_text_input_focus_set_preedit_text (ClutterInputFocus *focus,
 
   text_input->preedit.cursor = pos;
   text_input->preedit.anchor = pos;
+  text_input->preedit.changed = TRUE;
 
   meta_wayland_text_input_focus_defer_done (focus);
 }