feat(extui): assign 'filetype' to extui windows (#33924)

Problem:  Unable to discern windows used by the extui interface
          to configure their local options.
          'winblend' may be detrimental to legibility depending on the
          colorscheme and 'background'.
Solution: Assign the "cmdline", "msgmore", "msgprompt" and "msgbox" 
          'filetype' to the respective windows.
          Don't set 'winblend' for the message "box" window.

1 files changed, 14 insertions, 9 deletions

diff --git a/runtime/lua/vim/_extui.lua b/runtime/lua/vim/_extui.lua
index 8b3f67076e..99a3dfa307 100644
--- a/runtime/lua/vim/_extui.lua
+++ b/runtime/lua/vim/_extui.lua
@@ -17,6 +17,19 @@
 ---  },
 ---})
 ---```
+---
+---There are four separate window types used by this interface:
+---- "cmd": The cmdline window; also used for 'showcmd', 'showmode', 'ruler', and
+---  messages if 'cmdheight' > 0.
+---- "box": The message box window; used for messages when 'cmdheight' == 0.
+---- "more": The more-prompt window; used for |:messages| and certain messages
+---   that should be shown in full.
+---- "prompt": The cmdline prompt window; used for prompt messages that expect
+---   user input.
+---
+---These four windows are assigned the "cmdline", "msgbox", "msgmore" and
+---"msgprompt" 'filetype' respectively. Use a |FileType| autocommand to configure
+---any local options for these windows and their respective buffers.
 
 local api = vim.api
 local ext = require('vim._extui.shared')
@@ -90,24 +103,17 @@ function M.enable(opts)
         ext.msg.prev_msg = ''
       end
       ext.cmdheight = value
-    elseif name == 'termguicolors' then
-      -- 'termguicolors' toggled; add or remove border and set 'winblend' for box windows.
-      for _, tab in ipairs(api.nvim_list_tabpages()) do
-        api.nvim_win_set_config(ext.wins[tab].box, { border = value and 'none' or 'single' })
-        vim.wo[ext.wins[tab].box].winblend = value and 30 or 0
-      end
     end
   end
 
   if vim.v.vim_did_enter == 1 then
     ext.tab_check_wins()
     check_opt('cmdheight', vim.o.cmdheight)
-    check_opt('termguicolors', vim.o.termguicolors)
   end
 
   api.nvim_create_autocmd('OptionSet', {
     group = ext.augroup,
-    pattern = { 'cmdheight', 'termguicolors' },
+    pattern = { 'cmdheight' },
     callback = function(ev)
       ext.tab_check_wins()
       check_opt(ev.match, vim.v.option_new)
@@ -122,7 +128,6 @@ function M.enable(opts)
       ext.tab_check_wins()
       if ev.event == 'VimEnter' then
         check_opt('cmdheight', vim.o.cmdheight)
-        check_opt('termguicolors', vim.o.termguicolors)
       end
       ext.msg.set_pos()
     end,