From 4d3755770c8dad4b6cb7c9df441504aaadd18556 Mon Sep 17 00:00:00 2001
From: Eberhard Beilharz <eb1@sil.org>
Date: Mon, 20 Feb 2023 17:14:30 +0100
Subject: [PATCH] fix(linux): Collect consecutive backspaces

When using Wayland `im-wayland.so` (which is part of libgtk) gets
loaded into the client app instead of `im-ibus.so`. This means that
our ordered output doesn't work with Wayland.

This change works around a problem with keyboards that use multiple
consecutive backspace actions. Because method calls get processed
asynchronously some backspaces get lost. In clients that support
surrounding text we can count the consecutive backspaces and then
do one call to delete surrounding text with the appropriate number
of characters.

This can be tested with "Khmer Angkor" keyboard by typing `xEjmr`,
or with "Vedic Sanskrit Devanagari Phonetic (ITRANS)" keyboard by
typing `shrI`.

Part of #4273.
---
 linux/ibus-keyman/src/engine.c | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/linux/ibus-keyman/src/engine.c b/linux/ibus-keyman/src/engine.c
index 368fe94182..6273d3ecd9 100644
--- a/linux/ibus-keyman/src/engine.c
+++ b/linux/ibus-keyman/src/engine.c
@@ -99,6 +99,7 @@ struct _IBusKeymanEngine {
 
   commit_queue_item commit_queue[MAX_QUEUE_SIZE];
   commit_queue_item *commit_item;
+  guint             consecutive_backspaces;
 };
 
 struct _IBusKeymanEngineClass {
@@ -467,6 +468,7 @@ ibus_keyman_engine_constructor(
     keyman->lctrl_pressed = FALSE;
     keyman->ralt_pressed = FALSE;
     keyman->rctrl_pressed = FALSE;
+    keyman->consecutive_backspaces = 0;
     initialize_queue(keyman, 0, MAX_QUEUE_SIZE);
     keyman->commit_item    = &keyman->commit_queue[0];
     gchar **split_name     = g_strsplit(engine_name, ":", 2);
@@ -656,8 +658,8 @@ process_backspace_action(
         "DAR: %s - client_capabilities=%x, %x", __FUNCTION__, engine->client_capabilities, IBUS_CAP_SURROUNDING_TEXT);
 
     if (client_supports_surrounding_text(engine)) {
-      g_message("%s: deleting surrounding text 1 char", __FUNCTION__);
-      ibus_engine_delete_surrounding_text(engine, -1, 1);
+      keyman->consecutive_backspaces++;
+      g_message("%s: increment consecutive backspaces to %d", __FUNCTION__, keyman->consecutive_backspaces);
     } else {
       g_message("%s: forwarding backspace with reset context", __FUNCTION__);
       km_kbp_context_item *context_items;
@@ -671,6 +673,21 @@ process_backspace_action(
   return TRUE;
 }
 
+static gboolean
+finish_backspace_action(
+  IBusEngine *engine
+) {
+  IBusKeymanEngine *keyman = (IBusKeymanEngine *)engine;
+  if (keyman->consecutive_backspaces <= 0)
+    return TRUE;
+
+  g_assert(client_supports_surrounding_text(engine));
+  g_message("%s: deleting surrounding text %d char", __FUNCTION__, keyman->consecutive_backspaces);
+  ibus_engine_delete_surrounding_text(engine, -keyman->consecutive_backspaces, keyman->consecutive_backspaces);
+  keyman->consecutive_backspaces = 0;
+  return TRUE;
+}
+
 static gboolean
 process_persist_action(
   IBusKeymanEngine *keyman,
@@ -816,6 +833,9 @@ process_actions(
   IBusKeymanEngine *keyman = (IBusKeymanEngine *)engine;
   for (int i = 0; i < num_action_items; i++) {
     gboolean continue_with_next_action = TRUE;
+    if (action_items[i].type != KM_KBP_IT_BACK && keyman->consecutive_backspaces > 0) {
+      finish_backspace_action(engine);
+    }
     switch (action_items[i].type) {
     case KM_KBP_IT_CHAR:
       g_message("CHAR action %d/%d", i + 1, (int)num_action_items);