fix(ui): superfluous showmode / excessive grid_cursor_goto #29089

Problem:  Unsetting global variables earlier in #28578 to avoid
          recursiveness, caused superfluous or even unlimited
          showmode().
Solution: Partly revert #28578 so that the globals are unset at the end
          of showmode(), and avoid recursiveness for ext UI by adding a
          recursive function guard to each generated UI call that may
          call a Lua callback.

1 files changed, 16 insertions, 0 deletions

diff --git a/test/functional/ui/messages_spec.lua b/test/functional/ui/messages_spec.lua
index ca52a265fa..07192800e5 100644
--- a/test/functional/ui/messages_spec.lua
+++ b/test/functional/ui/messages_spec.lua
@@ -1081,6 +1081,22 @@ stack traceback:
       },
     })
   end)
+
+  it('does not do showmode unnecessarily #29086', function()
+    local screen_showmode = screen._handle_msg_showmode
+    local showmode = 0
+    screen._handle_msg_showmode = function(...)
+      screen_showmode(...)
+      showmode = showmode + 1
+    end
+    screen:expect({
+      grid = [[
+        ^                         |
+        {1:~                        }|*4
+      ]],
+    })
+    eq(showmode, 1)
+  end)
 end)
 
 describe('ui/builtin messages', function()