vim-patch:9.0.1772: Cursor may be adjusted in 'splitkeep'ed windows (#24811)

Problem:    Cursor is adjusted in window that did not change in size by
            'splitkeep'.
Solution:   Only check that cursor position is valid in a window that
            has changed in size.

closes: vim/vim#12509

https://github.com/vim/vim/commit/16af913eeefb288ce968fb87e09a597413861900

Co-authored-by: Luuk van Baal <luukvbaal@gmail.com>

4 files changed, 95 insertions, 4 deletions

diff --git a/src/nvim/buffer_defs.h b/src/nvim/buffer_defs.h
index ca1f791d28..0a7c742798 100644
--- a/src/nvim/buffer_defs.h
+++ b/src/nvim/buffer_defs.h
@@ -1194,6 +1194,7 @@ struct window_S {
   int w_hsep_height;                // Number of horizontal separator rows (0 or 1)
   int w_vsep_width;                 // Number of vertical separator columns (0 or 1).
   pos_save_T w_save_cursor;         // backup of cursor pos and topline
+  bool w_do_win_fix_cursor;         // if true cursor may be invalid
 
   int w_winrow_off;  ///< offset from winrow to the inner window area
   int w_wincol_off;  ///< offset from wincol to the inner window area
diff --git a/src/nvim/window.c b/src/nvim/window.c
index e933390363..175a79568c 100644
--- a/src/nvim/window.c
+++ b/src/nvim/window.c
@@ -6465,6 +6465,10 @@ void win_fix_scroll(int resize)
   FOR_ALL_WINDOWS_IN_TAB(wp, curtab) {
     // Skip when window height has not changed or when floating.
     if (!wp->w_floating && wp->w_height != wp->w_prev_height) {
+      // Cursor position in this window may now be invalid.  It is kept
+      // potentially invalid until the window is made the current window.
+      wp->w_do_win_fix_cursor = true;
+
       // If window has moved update botline to keep the same screenlines.
       if (*p_spk == 's' && wp->w_winrow != wp->w_prev_winrow
           && wp->w_botline - 1 <= wp->w_buffer->b_ml.ml_line_count) {
@@ -6488,6 +6492,7 @@ void win_fix_scroll(int resize)
       } else if (wp == curwin) {
         wp->w_valid &= ~VALID_CROW;
       }
+
       invalidate_botline_win(wp);
       validate_botline(wp);
     }
@@ -6505,16 +6510,19 @@ void win_fix_scroll(int resize)
 
 /// Make sure the cursor position is valid for 'splitkeep'.
 /// If it is not, put the cursor position in the jumplist and move it.
-/// If we are not in normal mode ("normal" is zero), make it valid by scrolling
+/// If we are not in normal mode ("normal" is false), make it valid by scrolling
 /// instead.
-static void win_fix_cursor(int normal)
+static void win_fix_cursor(bool normal)
 {
   win_T *wp = curwin;
 
-  if (skip_win_fix_cursor || wp->w_buffer->b_ml.ml_line_count < wp->w_height) {
+  if (skip_win_fix_cursor
+      || !wp->w_do_win_fix_cursor
+      || wp->w_buffer->b_ml.ml_line_count < wp->w_height_inner) {
     return;
   }
 
+  wp->w_do_win_fix_cursor = false;
   // Determine valid cursor range.
   int so = MIN(wp->w_height_inner / 2, get_scrolloff_value(wp));
   linenr_T lnum = wp->w_cursor.lnum;
@@ -6533,7 +6541,7 @@ static void win_fix_cursor(int normal)
   if (lnum > bot && (wp->w_botline - wp->w_buffer->b_ml.ml_line_count) != 1) {
     nlnum = bot;
   } else if (lnum < top && wp->w_topline != 1) {
-    nlnum = (so == wp->w_height / 2) ? bot : top;
+    nlnum = (so == wp->w_height_inner / 2) ? bot : top;
   }
 
   if (nlnum != 0) {  // Cursor is invalid for current scroll position.
diff --git a/test/functional/legacy/window_cmd_spec.lua b/test/functional/legacy/window_cmd_spec.lua
index 373a9c7163..979b46ae47 100644
--- a/test/functional/legacy/window_cmd_spec.lua
+++ b/test/functional/legacy/window_cmd_spec.lua
@@ -43,6 +43,61 @@ describe('splitkeep', function()
     screen:attach()
   end)
 
+  -- oldtest: Test_splitkeep_cursor()
+  it('does not adjust cursor in window that did not change size', function()
+    screen:try_resize(75, 8)
+    -- FIXME: bottom window is different without the "vsplit | close"
+    exec([[
+      vsplit | close
+      set scrolloff=5
+      set splitkeep=screen
+      autocmd CursorMoved * wincmd p | wincmd p
+      call setline(1, range(1, 200))
+      func CursorEqualize()
+        call cursor(100, 1)
+        wincmd =
+      endfunc
+      wincmd s
+      call CursorEqualize()
+    ]])
+
+    screen:expect([[
+      99                                                                         |
+      ^100                                                                        |
+      101                                                                        |
+      [No Name] [+]                                                              |
+      5                                                                          |
+      6                                                                          |
+      [No Name] [+]                                                              |
+                                                                                 |
+    ]])
+
+    feed('j')
+    screen:expect([[
+      100                                                                        |
+      ^101                                                                        |
+      102                                                                        |
+      [No Name] [+]                                                              |
+      5                                                                          |
+      6                                                                          |
+      [No Name] [+]                                                              |
+                                                                                 |
+    ]])
+
+    command('set scrolloff=0')
+    feed('G')
+    screen:expect([[
+      198                                                                        |
+      199                                                                        |
+      ^200                                                                        |
+      [No Name] [+]                                                              |
+      5                                                                          |
+      6                                                                          |
+      [No Name] [+]                                                              |
+                                                                                 |
+    ]])
+  end)
+
   -- oldtest: Test_splitkeep_callback()
   it('does not scroll when split in callback', function()
     exec([[
diff --git a/test/old/testdir/test_window_cmd.vim b/test/old/testdir/test_window_cmd.vim
index 7d4932a2b5..bd4cb44b2b 100644
--- a/test/old/testdir/test_window_cmd.vim
+++ b/test/old/testdir/test_window_cmd.vim
@@ -1805,6 +1805,33 @@ func Test_splitkeep_misc()
   set splitkeep&
 endfunc
 
+func Test_splitkeep_cursor()
+  CheckScreendump
+  let lines =<< trim END
+    set splitkeep=screen
+    autocmd CursorMoved * wincmd p | wincmd p
+    call setline(1, range(1, 200))
+    func CursorEqualize()
+      call cursor(100, 1)
+      wincmd =
+    endfunc
+    wincmd s
+    call CursorEqualize()
+  END
+  call writefile(lines, 'XTestSplitkeepCallback', 'D')
+  let buf = RunVimInTerminal('-S XTestSplitkeepCallback', #{rows: 8})
+
+  call VerifyScreenDump(buf, 'Test_splitkeep_cursor_1', {})
+
+  call term_sendkeys(buf, "j")
+  call VerifyScreenDump(buf, 'Test_splitkeep_cursor_2', {})
+
+  call term_sendkeys(buf, ":set scrolloff=0\<CR>G")
+  call VerifyScreenDump(buf, 'Test_splitkeep_cursor_3', {})
+
+  call StopVimInTerminal(buf)
+endfunc
+
 func Test_splitkeep_callback()
   CheckScreendump
   let lines =<< trim END