fix(grid): double grid_line_start() with ext_messages #31292

Problem:  Hit double grid_line_start() assert when redrawing from
          ext_messages msg_ruler event.
Solution: Do not start() batched grid calls when win_redr_ruler() will not
          puts() anything.

1 files changed, 15 insertions, 0 deletions

diff --git a/test/functional/ui/messages_spec.lua b/test/functional/ui/messages_spec.lua
index 9a6dfd8ed1..164b840b35 100644
--- a/test/functional/ui/messages_spec.lua
+++ b/test/functional/ui/messages_spec.lua
@@ -1159,6 +1159,21 @@ stack traceback:
     exec_lua([[vim.print({ foo = "bar" })]])
     screen:expect_unchanged()
   end)
+
+  it('ruler redraw does not crash due to double grid_line_start()', function()
+    exec_lua([[
+      local ns = vim.api.nvim_create_namespace('')
+      vim.ui_attach(ns, { ext_messages = true }, function(event, ...)
+        if event == 'msg_ruler' then
+          vim.api.nvim__redraw({ flush = true })
+        end
+      end)
+      vim.o.ruler = true
+      vim.o.laststatus = 0
+    ]])
+    feed('i')
+    n.assert_alive()
+  end)
 end)
 
 describe('ui/builtin messages', function()