fix(cmdline): avoid redraw loop after wrapped line #40240

Problem:  A wrapped command line and screen width may be redrawn
          repeatedly after calls to `redrawstatus` from lua.

Solution: redrawcmd() redraws the command line, but msg_clr_eos() may
          invalidate cmdline_was_last_drawn during the redraw process.
          Restore cmdline_was_last_drawn when redrawcmd() completes.

Co-authored-by: Sam Reynoso <sam@codeoutpost.com>
Co-authored-by: Luuk van Baal <luukvbaal@gmail.com>
(cherry picked from commit 6be9459d35)

src/nvim/ex_getln.c

@@ -4069,7 +4069,7 @@ void redrawcmd(void)
   // Typing ':' at the more prompt may set skip_redraw.  We don't want this
   // in cmdline mode.
   skip_redraw = false;
-
+  cmdline_was_last_drawn = true;
   redrawing_cmdline = false;
 }
 

test/functional/ui/cmdline_spec.lua

@@ -1061,6 +1061,27 @@ describe('cmdline redraw', function()
       1 substitution on 1 line                                                   |
     ]])
   end)
+
+  it('no empty cmdline after empty echo #18274', function()
+    feed(':foo')
+    api.nvim_echo({ { '' } }, false, {})
+    screen:expect([[
+                               |
+      {1:~                        }|*3
+      :foo^                     |
+    ]])
+    feed(('o'):rep(screen._width - 4))
+    -- No repeated cmdline redraws at screen width
+    screen:expect([[
+                               |
+      {1:~                        }|
+      {3:                         }|
+      :fooooooooooooooooooooooo|
+      ^                         |
+    ]])
+    command('call timer_start(0, {-> 1})')
+    screen:expect_unchanged()
+  end)
 end)
 
 describe('statusline is redrawn on entering cmdline', function()