From f9040dbe03e0775cd7e9a8b89c0d8fb8d938c2b0 Mon Sep 17 00:00:00 2001
From: zeertzjq <zeertzjq@outlook.com>
Date: Fri, 31 Jul 2026 10:50:57 +0800
Subject: [PATCH] vim-patch:9.2.0880: scroll: window scrolls when using the
 autocommand window

Problem:  The window scrolls when an autocommand window is used while the
          cursor is behind multi-byte characters.
Solution: Use the byte column instead of the character count when computing
          how many screen lines the text up to the cursor takes.

fixes:  vim/vim#12085
closes: vim/vim#20884

https://github.com/vim/vim/commit/7fe3ea7658a1f3be4e07dee14041302ca129c8a9

Co-authored-by: Hirohito Higashi <h.east.727@gmail.com>
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
---
 src/nvim/plines.c                    |  6 +++---
 test/old/testdir/test_window_cmd.vim | 18 ++++++++++++++++++
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/src/nvim/plines.c b/src/nvim/plines.c
index 3925bfbdc0..a2ae392e95 100644
--- a/src/nvim/plines.c
+++ b/src/nvim/plines.c
@@ -814,7 +814,7 @@ int plines_win_nofold(win_T *wp, linenr_T lnum)
 }
 
 /// Like plines_win(), but only reports the number of physical screen lines
-/// used from the start of the line to the given column number.
+/// used from the start of the line to the given byte column.
 int plines_win_col(win_T *wp, linenr_T lnum, long column)
 {
   // Check for filler lines above this buffer line.
@@ -837,12 +837,12 @@ int plines_win_col(win_T *wp, linenr_T lnum, long column)
   StrCharInfo ci = utf_ptr2StrCharInfo(line);
   if (cstype == kCharsizeFast) {
     bool const use_tabstop = csarg.use_tabstop;
-    while (*ci.ptr != NUL && --column >= 0) {
+    while (*ci.ptr != NUL && ci.ptr < line + column) {
       vcol += charsize_fast_impl(wp, ci.ptr, use_tabstop, vcol, ci.chr.value).width;
       ci = utfc_next(ci);
     }
   } else {
-    while (*ci.ptr != NUL && --column >= 0) {
+    while (*ci.ptr != NUL && ci.ptr < line + column) {
       vcol += charsize_regular(&csarg, ci.ptr, vcol, ci.chr.value).width;
       ci = utfc_next(ci);
     }
diff --git a/test/old/testdir/test_window_cmd.vim b/test/old/testdir/test_window_cmd.vim
index 783829221e..70337df60f 100644
--- a/test/old/testdir/test_window_cmd.vim
+++ b/test/old/testdir/test_window_cmd.vim
@@ -1989,6 +1989,24 @@ func Test_splitkeep_cmdheight()
   set splitkeep& cmdheight&
 endfunc
 
+func Test_aucmd_win_scroll_multibyte()
+  " Using the autocommand window must not scroll the current window when the
+  " cursor is behind multi-byte characters.
+  set splitkeep=cursor
+  call setline(1, repeat([repeat(nr2char(0x3042), 200)], 20))
+  normal! G0100l
+  redraw
+  let topline = line('w0')
+
+  for i in range(3)
+    call bufload(bufadd(''))
+  endfor
+  call assert_equal(topline, line('w0'))
+
+  %bwipeout!
+  set splitkeep&
+endfunc
+
 func Test_splitkeep_cursor()
   CheckScreendump
   let lines =<< trim END