feat(ui): completeopt support popup like vim

runtime/lua/vim/_meta/api.lua

@@ -773,6 +773,16 @@ function vim.api.nvim_command(command) end
 --- @return string
 function vim.api.nvim_command_output(command) end
 
+--- Set info for the completion candidate index. if the info was shown in a
+--- window, then the window and buffer ids are returned for further
+--- customization. If the text was not shown, an empty dict is returned.
+---
+--- @param index integer the completion candidate index
+--- @param opts vim.api.keyset.complete_set Optional parameters.
+---              • info: (string) info text.
+--- @return table<string,any>
+function vim.api.nvim_complete_set(index, opts) end
+
 --- Create or get an autocommand group `autocmd-groups`.
 --- To get an existing group id, do:
 ---

runtime/lua/vim/_meta/api_keysets.lua

@@ -68,6 +68,9 @@ error('Cannot require a meta file')
 --- @class vim.api.keyset.cmd_opts
 --- @field output? boolean
 
+--- @class vim.api.keyset.complete_set
+--- @field info? string
+
 --- @class vim.api.keyset.context
 --- @field types? any[]
 

runtime/lua/vim/_meta/options.lua

@@ -1061,6 +1061,10 @@ vim.bo.cfu = vim.bo.completefunc
 --- 	    select one from the menu. Only works in combination with
 --- 	    "menu" or "menuone".
 ---
+---    popup    Show extra information about the currently selected
+--- 	    completion in a popup window.  Only works in combination
+--- 	    with "menu" or "menuone".  Overrides "preview".
+---
 --- @type string
 vim.o.completeopt = "menu,preview"
 vim.o.cot = vim.o.completeopt

runtime/lua/vim/_meta/vimfn.lua

@@ -1024,6 +1024,8 @@ function vim.fn.complete_check() end
 ---     no item is selected when using the <Up> or
 ---     <Down> keys)
 ---    inserted  Inserted string. [NOT IMPLEMENTED YET]
+---    preview_winid     Info floating preview window id.
+---    preview_bufnr     Info floating preview buffer id.
 ---
 ---           *complete_info_mode*
 --- mode values are: