fix(cmdline): redraw cmdline after empty message (#38485)

Problem: Cmdline is not redrawn after an empty message clears it.
Remembered last drawn cursor position may be outdated but
equal to the current cmdline content with UI2.
Solution: Ensure cmdline is redrawn after an empty message clears it.
Compare wanted cursor position with actual cursor position.

runtime/lua/vim/_core/ui2/cmdline.lua

@@ -121,23 +121,22 @@ function M.cmdline_special_char(c, shift)
   end)
 end
 
-local curpos = { 0, 0 } -- Last drawn cursor position.
 --- Set the cmdline cursor position.
 ---
 ---@param pos integer
 --@param level integer
 function M.cmdline_pos(pos)
+  local curpos = api.nvim_win_get_cursor(ui.wins.cmd)
   pos = #fn.strtrans(cmdbuff:sub(1, pos))
   if curpos[1] ~= M.erow + 1 or curpos[2] ~= promptlen + pos then
-    curpos[1], curpos[2] = M.erow + 1, promptlen + pos
     -- Add matchparen highlighting to non-prompt part of cmdline.
     if pos > 0 and fn.exists('#matchparen#CursorMoved') == 1 then
-      api.nvim_win_set_cursor(ui.wins.cmd, { curpos[1], curpos[2] - 1 })
+      api.nvim_win_set_cursor(ui.wins.cmd, { M.erow + 1, promptlen + pos - 1 })
       vim._with({ win = ui.wins.cmd, wo = { eventignorewin = '' } }, function()
         api.nvim_exec_autocmds('CursorMoved', {})
       end)
     end
-    api.nvim_win_set_cursor(ui.wins.cmd, curpos)
+    api.nvim_win_set_cursor(ui.wins.cmd, { M.erow + 1, promptlen + pos })
   end
 end
 
@@ -176,7 +175,7 @@ function M.cmdline_hide(level, abort)
     end
   end)
 
-  M.prompt, M.level, curpos[1], curpos[2] = false, 0, 0, 0
+  M.prompt, M.level = false, 0
   win_config(ui.wins.cmd, true, ui.cmdheight)
 end
 

src/nvim/message.c

@@ -2338,6 +2338,7 @@ void msg_puts_len(const char *const str, const ptrdiff_t len, int hl_id, bool hi
     if (*str == NUL && ui_has(kUIMessages)) {
       ui_call_msg_show(cstr_as_string("empty"), (Array)ARRAY_DICT_INIT, false, false, false,
                        INTEGER_OBJ(-1), (String)STRING_INIT);
+      cmdline_was_last_drawn = false;
     }
     return;
   }
@@ -3311,6 +3312,7 @@ void msg_clr_eos_force(void)
   if (msg_row < Rows - 1 || msg_col == 0) {
     clear_cmdline = false;  // command line has been cleared
     mode_displayed = false;  // mode cleared or overwritten
+    cmdline_was_last_drawn = false;
   }
 }
 

test/functional/ui/cmdline2_spec.lua

@@ -172,7 +172,7 @@ describe('cmdline2', function()
     t.eq(n.eval('v:errmsg'), "E1514: 'findfunc' did not return a List type")
   end)
 
-  it('substitution match does not clear cmdline', function()
+  it('substitution match, empty message does not clear active cmdline', function()
     exec('call setline(1, "foo")')
     feed(':s/f')
     screen:expect([[
@@ -180,6 +180,14 @@ describe('cmdline2', function()
       {1:~                                                    }|*12
       {16::}{15:s}{16:/f^ }                                                |
     ]])
+    feed('<Esc>:foo')
+    screen:expect([[
+      foo                                                  |
+      {1:~                                                    }|*12
+      {16::}{15:foo}^                                                 |
+    ]])
+    exec('echo')
+    screen:expect_unchanged(true)
   end)
 
   it('dialog position is adjusted for toggled non-pum wildmenu', function()