From 0b91e9f83b8807bf3fb584a70607deb1360824bd Mon Sep 17 00:00:00 2001
From: luukvbaal <luukvbaal@gmail.com>
Date: Fri, 27 Jun 2025 11:16:23 +0200
Subject: [PATCH] vim-patch:9.1.1482: scrolling with 'splitkeep' and line()
 (#34670)

Problem:  Topline is preemptively updated by line() in WinResized
          autocmd with 'splitkeep' != "cursor".
Solution: Set `skip_update_topline` when 'splitkeep' != "cursor".
          (Luuk van Baal)

https://github.com/vim/vim/commit/fe803c8c04c1b73453c0dab970863ab53e3eeec7
---
 src/nvim/eval/funcs.c                      | 10 ++++----
 test/functional/legacy/window_cmd_spec.lua | 27 ++++++++++++++++++++++
 test/old/testdir/test_window_cmd.vim       | 18 +++++++++++++++
 3 files changed, 49 insertions(+), 6 deletions(-)

diff --git a/src/nvim/eval/funcs.c b/src/nvim/eval/funcs.c
index 126935837e..6f98d0eb5f 100644
--- a/src/nvim/eval/funcs.c
+++ b/src/nvim/eval/funcs.c
@@ -4379,17 +4379,15 @@ static void f_line(typval_T *argvars, typval_T *rettv, EvalFuncData fptr)
     if (wp != NULL && tp != NULL) {
       switchwin_T switchwin;
       if (switch_win_noblock(&switchwin, wp, tp, true) == OK) {
-        // in diff mode, prevent that the window scrolls
-        // and keep the topline
-        if (curwin->w_p_diff && switchwin.sw_curwin->w_p_diff) {
+        // With 'splitkeep' != cursor and in diff mode, prevent that the
+        // window scrolls and keep the topline.
+        if (*p_spk != 'c' || (curwin->w_p_diff && switchwin.sw_curwin->w_p_diff)) {
           skip_update_topline = true;
         }
         check_cursor(curwin);
         fp = var2fpos(&argvars[0], true, &fnum, false);
       }
-      if (curwin->w_p_diff && switchwin.sw_curwin->w_p_diff) {
-        skip_update_topline = false;
-      }
+      skip_update_topline = false;
       restore_win_noblock(&switchwin, true);
     }
   } else {
diff --git a/test/functional/legacy/window_cmd_spec.lua b/test/functional/legacy/window_cmd_spec.lua
index fac982354c..37d1101ff2 100644
--- a/test/functional/legacy/window_cmd_spec.lua
+++ b/test/functional/legacy/window_cmd_spec.lua
@@ -326,4 +326,31 @@ describe('splitkeep', function()
                                               |
     ]])
   end)
+
+  -- oldtest: Test_splitkeep_line()
+  it("no scrolling with 'splitkeep' and line()", function()
+    screen:try_resize(40, 6)
+    exec([[
+      set splitkeep=screen nosplitbelow
+      autocmd WinResized * call line('w0', 1000)
+      call setline(1, range(1000))
+    ]])
+    screen:expect([[
+      ^0                                       |
+      1                                       |
+      2                                       |
+      3                                       |
+      4                                       |
+                                              |
+    ]])
+    feed(':wincmd s<CR>')
+    screen:expect([[
+      ^0                                       |
+      1                                       |
+      {3:[No Name] [+]                           }|
+      3                                       |
+      {2:[No Name] [+]                           }|
+      :wincmd s                               |
+    ]])
+  end)
 end)
diff --git a/test/old/testdir/test_window_cmd.vim b/test/old/testdir/test_window_cmd.vim
index 3501672f95..ae59adbc6e 100644
--- a/test/old/testdir/test_window_cmd.vim
+++ b/test/old/testdir/test_window_cmd.vim
@@ -2075,6 +2075,24 @@ func Test_splitkeep_skipcol()
   call VerifyScreenDump(buf, 'Test_splitkeep_skipcol_1', {})
 endfunc
 
+func Test_splitkeep_line()
+  CheckScreendump
+
+  let lines =<< trim END
+    set splitkeep=screen nosplitbelow
+    autocmd WinResized * call line('w0', 1000)
+    call setline(1, range(1000))
+  END
+
+  call writefile(lines, 'XTestSplitkeepSkipcol', 'D')
+  let buf = RunVimInTerminal('-S XTestSplitkeepSkipcol', #{rows: 6, cols: 40})
+
+  call VerifyScreenDump(buf, 'Test_splitkeep_line_1', {})
+
+  call term_sendkeys(buf, ":wincmd s\<CR>")
+  call VerifyScreenDump(buf, 'Test_splitkeep_line_2', {})
+endfunc
+
 func Test_new_help_window_on_error()
   help change.txt
   execute "normal! /CTRL-@\<CR>"