From f57f3d99091a105cbd9484c33264558785efc4be Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Fri, 21 Mar 2025 19:55:45 +0530
Subject: [PATCH] Fix #8464

---
 docs/changelog.rst       |  3 +++
 kitty/resize.c           | 15 ++++-----------
 kitty_tests/multicell.py |  5 +++++
 3 files changed, 12 insertions(+), 11 deletions(-)

diff --git a/docs/changelog.rst b/docs/changelog.rst
index 502ee0119..b20c1a39f 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -110,6 +110,9 @@ Detailed list of changes
 - Fix a regression in version 0.40.0 causing a crash when the underline
   thickness of the font is zero (:iss:`8443`)
 
+- Fix a regression in version 0.40.0 causing a hang on resizing with a wide
+  character at the right edge of a line that needs to be moved onto the next
+  line (:iss:`8464`)
 
 0.40.1 [2025-03-18]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/kitty/resize.c b/kitty/resize.c
index 78980b788..280495fab 100644
--- a/kitty/resize.c
+++ b/kitty/resize.c
@@ -228,7 +228,7 @@ multiline_copy_src_to_dest(Rewrap *r) {
 
 static void
 fast_copy_src_to_dest(Rewrap *r) {
-    CPUCell *c; index_type mc_width;
+    CPUCell *c;
     while (r->src.x < r->src_x_limit) {
         if (r->dest.x >= dest_xnum) {
             next_dest_line(r, true);
@@ -238,17 +238,10 @@ fast_copy_src_to_dest(Rewrap *r) {
             }
         }
         index_type num = MIN(r->src_x_limit - r->src.x, dest_xnum - r->dest.x);
-        if (num && (c = &r->src.line.cpu_cells[r->src.x + num - 1])->is_multicell && c->x != (mc_width = mcd_x_limit(c)) - 1) {
+        if (num && (c = &r->src.line.cpu_cells[r->src.x + num - 1])->is_multicell && c->x != mcd_x_limit(c) - 1) {
             // we have a split multicell at the right edge of the copy region
-            if (num > mc_width) num = MIN(r->src_x_limit - r->src.x - mc_width, num);
-            else {
-                if (mc_width > dest_xnum) {
-                    multiline_copy_src_to_dest(r);
-                    return;
-                }
-                r->dest.x = dest_xnum;
-                continue;
-            }
+            multiline_copy_src_to_dest(r);
+            return;
         }
         copy_range(&r->src.line, r->src.x, &r->dest.line, r->dest.x, num);
         update_tracked_cursors(r, num, r->src.y, r->dest.y, r->src_x_limit);
diff --git a/kitty_tests/multicell.py b/kitty_tests/multicell.py
index 63e9892b8..94c2010c9 100644
--- a/kitty_tests/multicell.py
+++ b/kitty_tests/multicell.py
@@ -98,6 +98,11 @@ def test_multicell(self: TestMulticell) -> None:
     def assert_cursor_at(x, y):
         self.ae((s.cursor.x, s.cursor.y), (x, y))
 
+    s = self.create_screen(cols=8, lines=4)
+    s.draw('飛青進服三上')
+    s.resize(s.lines, 5)
+    self.ae('飛青', str(s.line(0)))
+
     s = self.create_screen(cols=6, lines=6)
 
     # Test basic multicell drawing