vim-patch:9.0.1491: wrong scrolling with ls=0 and :botright split (#23333)

Problem:    Wrong scrolling with ls=0 and :botright split.
Solution:   Add statusline before calling frame_new_height(). (closes vim/vim#12299)

fbf2071ac9

src/nvim/window.c

@@ -1448,7 +1448,7 @@ int win_split_ins(int size, int flags, win_T *new_wp, int dir)
     frame_fix_width(oldwin);
     frame_fix_width(wp);
   } else {
-    bool is_stl_global = global_stl_height() > 0;
+    const bool is_stl_global = global_stl_height() > 0;
     // width and column of new window is same as current window
     if (flags & (WSP_TOP | WSP_BOT)) {
       wp->w_wincol = 0;
@@ -1464,6 +1464,7 @@ int win_split_ins(int size, int flags, win_T *new_wp, int dir)
     // "new_size" of the current window goes to the new window, use
     // one row for the status line
     win_new_height(wp, new_size);
+    const int old_status_height = oldwin->w_status_height;
     if (before) {
       wp->w_hsep_height = is_stl_global ? 1 : 0;
     } else {
@@ -1472,15 +1473,19 @@ int win_split_ins(int size, int flags, win_T *new_wp, int dir)
     }
     if (flags & (WSP_TOP | WSP_BOT)) {
       int new_fr_height = curfrp->fr_height - new_size;
-
-      if (!((flags & WSP_BOT) && p_ls == 0) && !is_stl_global) {
-        new_fr_height -= STATUS_HEIGHT;
-      } else if (is_stl_global) {
+      if (is_stl_global) {
         if (flags & WSP_BOT) {
           frame_add_hsep(curfrp);
         } else {
           new_fr_height -= 1;
         }
+      } else {
+        if (!((flags & WSP_BOT) && p_ls == 0)) {
+          new_fr_height -= STATUS_HEIGHT;
+        }
+        if (flags & WSP_BOT) {
+          frame_add_statusline(curfrp);
+        }
       }
       frame_new_height(curfrp, new_fr_height, flags & WSP_TOP, false);
     } else {
@@ -1489,7 +1494,6 @@ int win_split_ins(int size, int flags, win_T *new_wp, int dir)
 
     if (before) {       // new window above current one
       wp->w_winrow = oldwin->w_winrow;
-
       if (is_stl_global) {
         wp->w_status_height = 0;
         oldwin->w_winrow += wp->w_height + 1;
@@ -1503,15 +1507,12 @@ int win_split_ins(int size, int flags, win_T *new_wp, int dir)
         wp->w_status_height = 0;
       } else {
         wp->w_winrow = oldwin->w_winrow + oldwin->w_height + STATUS_HEIGHT;
-        wp->w_status_height = oldwin->w_status_height;
+        wp->w_status_height = old_status_height;
         if (!(flags & WSP_BOT)) {
           oldwin->w_status_height = STATUS_HEIGHT;
         }
       }
     }
-    if ((flags & WSP_BOT) && !is_stl_global) {
-      frame_add_statusline(curfrp);
-    }
     frame_fix_height(wp);
     frame_fix_height(oldwin);
   }
@@ -3590,12 +3591,7 @@ static void frame_add_statusline(frame_T *frp)
 {
   if (frp->fr_layout == FR_LEAF) {
     win_T *wp = frp->fr_win;
-    if (wp->w_status_height == 0) {
-      if (wp->w_height - STATUS_HEIGHT >= 0) {           // don't make it negative
-        wp->w_height -= STATUS_HEIGHT;
-      }
-      wp->w_status_height = STATUS_HEIGHT;
-    }
+    wp->w_status_height = STATUS_HEIGHT;
   } else if (frp->fr_layout == FR_ROW) {
     // Handle all the frames in the row.
     FOR_ALL_FRAMES(frp, frp->fr_child) {

test/functional/legacy/window_cmd_spec.lua

@@ -3,8 +3,37 @@ local Screen = require('test.functional.ui.screen')
 local clear = helpers.clear
 local exec = helpers.exec
 local exec_lua = helpers.exec_lua
+local command = helpers.command
 local feed = helpers.feed
 
+-- oldtest: Test_window_cmd_ls0_split_scrolling()
+it('scrolling with laststatus=0 and :botright split', function()
+  clear('--cmd', 'set ruler')
+  local screen = Screen.new(40, 10)
+  screen:set_default_attr_ids({
+    [1] = {reverse = true},  -- StatusLineNC
+  })
+  screen:attach()
+  exec([[
+    set laststatus=0
+    call setline(1, range(1, 100))
+    normal! G
+  ]])
+  command('botright split')
+  screen:expect([[
+    97                                      |
+    98                                      |
+    99                                      |
+    100                                     |
+    {1:[No Name] [+]         100,1          Bot}|
+    97                                      |
+    98                                      |
+    99                                      |
+    ^100                                     |
+                          100,1         Bot |
+  ]])
+end)
+
 describe('splitkeep', function()
   local screen
 

test/old/testdir/test_window_cmd.vim

@@ -19,6 +19,24 @@ func Test_window_cmd_ls0_with_split()
   set ls&vim
 endfunc
 
+func Test_window_cmd_ls0_split_scrolling()
+  CheckRunVimInTerminal
+
+  let lines =<< trim END
+    set laststatus=0
+    call setline(1, range(1, 100))
+    normal! G
+  END
+  call writefile(lines, 'XTestLs0SplitScrolling', 'D')
+  let buf = RunVimInTerminal('-S XTestLs0SplitScrolling', #{rows: 10})
+
+  call term_sendkeys(buf, ":botright split\<CR>")
+  call WaitForAssert({-> assert_match('Bot$', term_getline(buf, 5))})
+  call assert_equal('100', term_getline(buf, 4))
+
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_window_cmd_cmdwin_with_vsp()
   let efmt = 'Expected 0 but got %d (in ls=%d, %s window)'
   for v in range(0, 2)