vim-patch:8.2.4591: cursor line not updated when a callback moves the cursor

Problem:    Cursor line not updated when a callback moves the cursor.
Solution:   Check if the cursor moved. (closes vim/vim#9970)
https://github.com/vim/vim/commit/e7a74d53754765f22ef8ce71c915bb669d5f7f3f

redraw_after_callback() is N/A. Nvim handles timers on the main loop.

4 files changed, 83 insertions, 8 deletions

diff --git a/src/nvim/normal.c b/src/nvim/normal.c
index f402865d2d..e773351d63 100644
--- a/src/nvim/normal.c
+++ b/src/nvim/normal.c
@@ -1296,13 +1296,7 @@ static void normal_redraw(NormalState *s)
   }
 
   // Might need to update for 'cursorline'.
-  // When 'cursorlineopt' is "screenline" need to redraw always.
-  if (curwin->w_p_cul
-      && (curwin->w_last_cursorline != curwin->w_cursor.lnum
-          || (curwin->w_p_culopt_flags & CULOPT_SCRLINE))
-      && !char_avail()) {
-    redraw_later(curwin, VALID);
-  }
+  check_redraw_cursorline();
 
   if (VIsual_active) {
     update_curbuf(INVERTED);  // update inverted part
diff --git a/src/nvim/screen.c b/src/nvim/screen.c
index 0194149b1b..27011c6f1e 100644
--- a/src/nvim/screen.c
+++ b/src/nvim/screen.c
@@ -737,6 +737,9 @@ static void win_update(win_T *wp, DecorProviders *providers)
 #define DID_FOLD 3      // updated a folded line
   int did_update = DID_NONE;
   linenr_T syntax_last_parsed = 0;              // last parsed text line
+  // remember the current w_last_cursorline, it changes when drawing the new
+  // cursor line
+  linenr_T last_cursorline = wp->w_last_cursorline;
   linenr_T mod_top = 0;
   linenr_T mod_bot = 0;
   int save_got_int;
@@ -1368,7 +1371,7 @@ static void win_update(win_T *wp, DecorProviders *providers)
                         || (wp->w_match_head != NULL
                             && buf->b_mod_xlines != 0)))))
         || (wp->w_p_cul && (lnum == wp->w_cursor.lnum
-                            || lnum == wp->w_last_cursorline))) {
+                            || lnum == last_cursorline))) {
       if (lnum == mod_top) {
         top_to_mod = false;
       }
@@ -7615,3 +7618,15 @@ win_T *get_win_by_grid_handle(handle_T handle)
   return NULL;
 }
 
+/// Check if the cursor moved and 'cursorline' is set.  Mark for a VALID redraw
+/// if needed.
+void check_redraw_cursorline(void)
+{
+  // When 'cursorlineopt' is "screenline" need to redraw always.
+  if (curwin->w_p_cul
+      && (curwin->w_last_cursorline != curwin->w_cursor.lnum
+          || (curwin->w_p_culopt_flags & CULOPT_SCRLINE))
+      && !char_avail()) {
+    redraw_later(curwin, VALID);
+  }
+}
diff --git a/src/nvim/testdir/test_cursorline.vim b/src/nvim/testdir/test_cursorline.vim
index 39d8b901ed..bf049ec779 100644
--- a/src/nvim/testdir/test_cursorline.vim
+++ b/src/nvim/testdir/test_cursorline.vim
@@ -268,4 +268,30 @@ END
   call delete('Xtextfile')
 endfunc
 
+func Test_cursorline_callback()
+  CheckScreendump
+  CheckFeature timers
+
+  let lines =<< trim END
+      call setline(1, ['aaaaa', 'bbbbb', 'ccccc', 'ddddd'])
+      set cursorline
+      call cursor(4, 1)
+
+      func Func(timer)
+        call cursor(2, 1)
+      endfunc
+
+      call timer_start(300, 'Func')
+  END
+  call writefile(lines, 'Xcul_timer')
+
+  let buf = RunVimInTerminal('-S Xcul_timer', #{rows: 8})
+  call TermWait(buf, 310)
+  call VerifyScreenDump(buf, 'Test_cursorline_callback_1', {})
+
+  call StopVimInTerminal(buf)
+  call delete('Xcul_timer')
+endfunc
+
+
 " vim: shiftwidth=2 sts=2 expandtab
diff --git a/test/functional/ui/highlight_spec.lua b/test/functional/ui/highlight_spec.lua
index 64f0ba3419..559738ddab 100644
--- a/test/functional/ui/highlight_spec.lua
+++ b/test/functional/ui/highlight_spec.lua
@@ -1081,6 +1081,46 @@ describe('CursorLine and CursorLineNr highlights', function()
     ]])
   end)
 
+  it('is updated if cursor is moved up from timer vim-patch:8.2.4591', function()
+    local screen = Screen.new(50, 8)
+    screen:set_default_attr_ids({
+      [1] = {background = Screen.colors.Gray90},  -- CursorLine
+      [2] = {bold = true, foreground = Screen.colors.Blue1},  -- NonText
+    })
+    screen:attach()
+    exec([[
+      call setline(1, ['aaaaa', 'bbbbb', 'ccccc', 'ddddd'])
+      set cursorline
+      call cursor(4, 1)
+
+      func Func(timer)
+        call cursor(2, 1)
+      endfunc
+
+      call timer_start(300, 'Func')
+    ]])
+    screen:expect({grid = [[
+      aaaaa                                             |
+      bbbbb                                             |
+      ccccc                                             |
+      {1:^ddddd                                             }|
+      {2:~                                                 }|
+      {2:~                                                 }|
+      {2:~                                                 }|
+                                                        |
+    ]], timeout = 100})
+    screen:expect({grid = [[
+      aaaaa                                             |
+      {1:^bbbbb                                             }|
+      ccccc                                             |
+      ddddd                                             |
+      {2:~                                                 }|
+      {2:~                                                 }|
+      {2:~                                                 }|
+                                                        |
+    ]]})
+  end)
+
   it('with split windows in diff mode', function()
     local screen = Screen.new(50,12)
     screen:set_default_attr_ids({