perf(extui): delay creating windows, buffers and parser (#34665)

Problem:  vim._extui unconditionally creates windows, buffers and the
          Vimscript cmdline highlighter when it is first loaded.
Solution: Schedule first creation of the window so that first redraw
          happens sooner (still need to create at least the cmdline
          window asap as it can have a different highlight through
          hl-MsgArea; thus further delaying until the first event that
          needs a particular target seems redundant). Load the cmdline
          highlighter on the first cmdline_show event.

runtime/lua/vim/_extui.lua

@@ -40,7 +40,7 @@ local M = {}
 
 local function ui_callback(event, ...)
   local handler = ext.msg[event] or ext.cmd[event]
-  ext.tab_check_wins()
+  ext.check_targets()
   handler(...)
   api.nvim__redraw({
     flush = handler ~= ext.cmd.cmdline_hide or nil,
@@ -99,8 +99,8 @@ function M.enable(opts)
   -- dependent on some option values. Reconfigure windows when option value
   -- has changed and after VimEnter when the user configured value is known.
   -- TODO: Reconsider what is needed when this module is enabled by default early in startup.
-  local function check_opt(name, value)
+  local function check_cmdheight(value)
-    if name == 'cmdheight' then
+    ext.check_targets()
     -- 'cmdheight' set; (un)hide cmdline window and set its height.
     local cfg = { height = math.max(value, 1), hide = value == 0 }
     api.nvim_win_set_config(ext.wins.cmd, cfg)
@@ -111,32 +111,25 @@ function M.enable(opts)
     end
     ext.cmdheight = value
   end
-  end
 
-  ext.tab_check_wins()
+  vim.schedule(function()
-  check_opt('cmdheight', vim.o.cmdheight)
+    check_cmdheight(vim.o.cmdheight)
+  end)
 
   api.nvim_create_autocmd('OptionSet', {
     group = ext.augroup,
     pattern = { 'cmdheight' },
-    callback = function(ev)
+    callback = function()
-      ext.tab_check_wins()
+      check_cmdheight(vim.v.option_new)
-      check_opt(ev.match, vim.v.option_new)
       ext.msg.set_pos()
     end,
     desc = 'Set cmdline and message window dimensions for changed option values.',
   })
 
-  api.nvim_create_autocmd({ 'VimEnter', 'VimResized', 'TabEnter' }, {
+  api.nvim_create_autocmd({ 'VimResized', 'TabEnter' }, {
     group = ext.augroup,
-    callback = function(ev)
+    callback = ext.msg.set_pos,
-      ext.tab_check_wins()
+    desc = 'Set cmdline and message window dimensions after shell resize or tabpage change.',
-      if ev.event == 'VimEnter' then
-        check_opt('cmdheight', vim.o.cmdheight)
-      end
-      ext.msg.set_pos()
-    end,
-    desc = 'Set extui window dimensions after startup, shell resize or tabpage change.',
   })
 
   api.nvim_create_autocmd('WinEnter', {

runtime/lua/vim/_extui/cmdline.lua

@@ -30,7 +30,7 @@ local function win_config(win, hide, height)
   end
 end
 
-local cmdbuff ---@type string Stored cmdline used to calculate translation offset.
+local cmdbuff = '' ---@type string Stored cmdline used to calculate translation offset.
 local promptlen = 0 -- Current length of the prompt, stored for use in "cmdline_pos"
 --- Concatenate content chunks and set the text for the current row in the cmdline buffer.
 ---
@@ -57,6 +57,10 @@ end
 ---@param hl_id integer
 function M.cmdline_show(content, pos, firstc, prompt, indent, level, hl_id)
   M.level, M.indent, M.prompt = level, indent, M.prompt or #prompt > 0
+  if M.highlighter == nil then
+    local parser = assert(vim.treesitter.get_parser(ext.bufs.cmd, 'vim', {}))
+    M.highlighter = vim.treesitter.highlighter.new(parser)
+  end
   -- Only enable TS highlighter for Ex commands (not search or filter commands).
   M.highlighter.active[ext.bufs.cmd] = firstc == ':' and M.highlighter or nil
   if ext.msg.cmd.msg_row ~= -1 then

runtime/lua/vim/_extui/messages.lua

@@ -310,7 +310,9 @@ function M.show_msg(tar, content, replace_last, append, pager)
       end
 
       api.nvim_win_set_cursor(ext.wins[tar], { 1, 0 })
+      if ext.cmd.highlighter then
         ext.cmd.highlighter.active[ext.bufs.cmd] = nil
+      end
       -- Place [+x] indicator for lines that spill over 'cmdheight'.
       M.cmd.lines, M.cmd.msg_row = h.all, h.end_row
       local spill = M.cmd.lines > ext.cmdheight and ('[+%d]'):format(M.cmd.lines - ext.cmdheight)
@@ -455,9 +457,12 @@ function M.set_pos(type)
   local function win_set_pos(win)
     local texth = type and api.nvim_win_text_height(win, {}) or 0
     local height = type and math.min(texth.all, math.ceil(o.lines * 0.5))
+    local top = { vim.opt.fcs:get().horiz or o.ambw == 'single' and '─' or '-', 'WinSeparator' }
+    local border = (type == 'pager' or type == 'dialog') and { '', top, '', '', '', '', '', '' }
     local config = {
       hide = false,
       relative = 'laststatus',
+      border = border or nil,
       height = height,
       row = win == ext.wins.msg and 0 or 1,
       col = 10000,

runtime/lua/vim/_extui/shared.lua

@@ -1,10 +1,10 @@
-local api, o = vim.api, vim.o
+local api = vim.api
 local M = {
   msg = nil, ---@type vim._extui.messages
   cmd = nil, ---@type vim._extui.cmdline
   ns = api.nvim_create_namespace('nvim._ext_ui'),
   augroup = api.nvim_create_augroup('nvim._ext_ui', {}),
-  cmdheight = -1, -- 'cmdheight' option value set by user.
+  cmdheight = 1, -- 'cmdheight' option value set by user.
   wins = { cmd = -1, dialog = -1, msg = -1, pager = -1 },
   bufs = { cmd = -1, dialog = -1, msg = -1, pager = -1 },
   cfg = {
@@ -28,18 +28,13 @@ local wincfg = { -- Default cfg for nvim_open_win().
 }
 
 local tab = 0
---- Ensure the various buffers and windows have not been deleted.
+---Ensure target buffers and windows are still valid.
-function M.tab_check_wins()
+function M.check_targets()
   local curtab = api.nvim_get_current_tabpage()
   for _, type in ipairs({ 'cmd', 'dialog', 'msg', 'pager' }) do
     local setopt = not api.nvim_buf_is_valid(M.bufs[type])
     if setopt then
       M.bufs[type] = api.nvim_create_buf(false, true)
-      if type == 'cmd' then
-        -- Attach highlighter to the cmdline buffer.
-        local parser = assert(vim.treesitter.get_parser(M.bufs.cmd, 'vim', {}))
-        M.cmd.highlighter = vim.treesitter.highlighter.new(parser)
-      end
     end
 
     if
@@ -47,15 +42,12 @@ function M.tab_check_wins()
       or not api.nvim_win_is_valid(M.wins[type])
       or not api.nvim_win_get_config(M.wins[type]).zindex -- no longer floating
     then
-      local top = { vim.opt.fcs:get().horiz or o.ambw == 'single' and '─' or '-', 'WinSeparator' }
-      local border = (type == 'pager' or type == 'dialog') and { '', top, '', '', '', '', '', '' }
       local cfg = vim.tbl_deep_extend('force', wincfg, {
         focusable = type == 'pager',
         mouse = type ~= 'cmd' and true or nil,
         anchor = type ~= 'cmd' and 'SE' or nil,
         hide = type ~= 'cmd' or M.cmdheight == 0 or nil,
-        title = type == 'pager' and 'Pager' or nil,
+        border = type == 'msg' and 'single' or 'none',
-        border = type == 'msg' and 'single' or border or 'none',
         -- kZIndexMessages < zindex < kZIndexCmdlinePopupMenu (grid_defs.h), pager below others.
         zindex = 200 - (type == 'pager' and 1 or 0),
         _cmdline_offset = type == 'cmd' and 0 or nil,

test/functional/ui/messages2_spec.lua

@@ -30,7 +30,7 @@ describe('messages2', function()
     screen:expect([[
                                                            |
       {1:~                                                    }|*9
-      ─{100:Pager}───────────────────────────────────────────────|
+      ─────────────────────────────────────────────────────|
       {4:fo^o                                                  }|
       {4:bar                                                  }|
       foo[+1]                             1,3           All|
@@ -40,7 +40,7 @@ describe('messages2', function()
     screen:expect([[
                                                            |
       {1:~                                                    }|*9
-      ─{100:Pager}───────────────────────────────────────────────|
+      ─────────────────────────────────────────────────────|
       {4:fo^o                                                  }|
       {4:bar                                                  }|
       {9:E354: Invalid register name: '^@'}   1,3           All|
@@ -50,7 +50,7 @@ describe('messages2', function()
     screen:expect([[
                                                            |
       {1:~                                                    }|*8
-      ─{100:Pager}───────────────────────────────────────────────|
+      ─────────────────────────────────────────────────────|
       {4:^foo                                                  }|
       {4:bar                                                  }|
       {4:baz                                                  }|
@@ -62,7 +62,7 @@ describe('messages2', function()
     screen:expect([[
                                                            |
       {1:~                                                    }|*7
-      ─{100:Pager}───────────────────────────────────────────────|
+      ─────────────────────────────────────────────────────|
       {4:^foo                                                  }|
       {4:bar                                                  }|
       {4:                                                     }|
@@ -89,7 +89,7 @@ describe('messages2', function()
     screen:expect([[
                                                            |
       {1:~                                                    }|*10
-      ─{100:Pager}───────────────────────────────────────────────|
+      ─────────────────────────────────────────────────────|
       {4:fo^o                                                  }|
       foo                                                  |
     ]])