fix(messages): reset msg_grid_scroll_discount when redrawing (#21000)

4 files changed, 17 insertions, 1 deletions

diff --git a/src/nvim/drawscreen.c b/src/nvim/drawscreen.c
index 30abcd1a31..b674f8c235 100644
--- a/src/nvim/drawscreen.c
+++ b/src/nvim/drawscreen.c
@@ -455,6 +455,7 @@ int update_screen(void)
     }
     msg_scrolled = 0;
     msg_scrolled_at_flush = 0;
+    msg_grid_scroll_discount = 0;
     need_wait_return = false;
   }
 
diff --git a/src/nvim/message.c b/src/nvim/message.c
index f274bd7289..314232d4be 100644
--- a/src/nvim/message.c
+++ b/src/nvim/message.c
@@ -130,7 +130,6 @@ static bool msg_ext_history_visible = false;
 static bool msg_ext_keep_after_cmdline = false;
 
 static int msg_grid_pos_at_flush = 0;
-static int msg_grid_scroll_discount = 0;
 
 static void ui_ext_msg_set_pos(int row, bool scrolled)
 {
@@ -2445,6 +2444,7 @@ void msg_reset_scroll(void)
   }
   msg_scrolled = 0;
   msg_scrolled_at_flush = 0;
+  msg_grid_scroll_discount = 0;
 }
 
 /// Increment "msg_scrolled".
diff --git a/src/nvim/message.h b/src/nvim/message.h
index 31cd54f18c..191d3b8da7 100644
--- a/src/nvim/message.h
+++ b/src/nvim/message.h
@@ -66,6 +66,8 @@ EXTERN ScreenGrid msg_grid_adj INIT(= SCREEN_GRID_INIT);
 // value of msg_scrolled at latest msg_scroll_flush.
 EXTERN int msg_scrolled_at_flush INIT(= 0);
 
+EXTERN int msg_grid_scroll_discount INIT(= 0);
+
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "message.h.generated.h"
 #endif
diff --git a/test/functional/ui/messages_spec.lua b/test/functional/ui/messages_spec.lua
index a042291b54..8ca29e79d9 100644
--- a/test/functional/ui/messages_spec.lua
+++ b/test/functional/ui/messages_spec.lua
@@ -10,9 +10,11 @@ local async_meths = helpers.async_meths
 local test_build_dir = helpers.test_build_dir
 local nvim_prog = helpers.nvim_prog
 local iswin = helpers.iswin
+local exec = helpers.exec
 local exc_exec = helpers.exc_exec
 local exec_lua = helpers.exec_lua
 local poke_eventloop = helpers.poke_eventloop
+local assert_alive = helpers.assert_alive
 
 describe('ui/ext_messages', function()
   local screen
@@ -1236,6 +1238,17 @@ vimComment     xxx match /\s"[^\-:.%#=*].*$/ms=s+1,lc=1  excludenl contains=@vim
   end)
 end)
 
+it('calling screenstring() after redrawing between messages without UI #20999', function()
+  clear()
+  exec([[
+    echo repeat('a', 100)
+    redraw
+    echo "\n"
+    call screenstring(1, 1)
+  ]])
+  assert_alive()
+end)
+
 describe('ui/ext_messages', function()
   local screen