fix(api): vim.filetype.get_option() (#22753)

- Fix a bug in the cache
- Set some buffer options on the dummy buffer

runtime/lua/vim/filetype/options.lua

@@ -3,7 +3,7 @@ local api = vim.api
 local M = {}
 
 local function get_ftplugin_runtime(filetype)
-  return api.nvim__get_runtime({
+  local files = api.nvim__get_runtime({
     string.format('ftplugin/%s.vim', filetype),
     string.format('ftplugin/%s_*.vim', filetype),
     string.format('ftplugin/%s/*.vim', filetype),
@@ -11,6 +11,15 @@ local function get_ftplugin_runtime(filetype)
     string.format('ftplugin/%s_*.lua', filetype),
     string.format('ftplugin/%s/*.lua', filetype),
   }, true, {}) --[[@as string[] ]]
+
+  local r = {} ---@type string[]
+  for _, f in ipairs(files) do
+    -- VIMRUNTIME should be static so shouldn't need to worry about it changing
+    if not vim.startswith(f, vim.env.VIMRUNTIME) then
+      r[#r + 1] = f
+    end
+  end
+  return r
 end
 
 -- Keep track of ftplugin files
@@ -52,8 +61,6 @@ local function update_ft_option_cache(filetype)
   end
 
   for _, f in ipairs(files) do
-    -- VIMRUNTIME should be static so shouldn't need to worry about it changing
-    if not vim.startswith(f, vim.env.VIMRUNTIME) then
     local mtime = hash(f)
     if ftplugin_cache[filetype][f] ~= mtime then
       -- invalidate
@@ -62,7 +69,6 @@ local function update_ft_option_cache(filetype)
     end
   end
 end
-end
 
 --- @private
 --- @param filetype string Filetype

src/nvim/api/options.c

@@ -111,6 +111,10 @@ static buf_T *do_ft_buf(char *filetype, aco_save_T *aco, Error *err)
 
   // Set curwin/curbuf to buf and save a few things.
   aucmd_prepbuf(aco, ftbuf);
+  set_option_value("bufhidden", 0L, "hide", OPT_LOCAL);
+  set_option_value("buftype", 0L, "nofile", OPT_LOCAL);
+  set_option_value("swapfile", 0L, NULL, OPT_LOCAL);
+  set_option_value("modeline", 0L, NULL, OPT_LOCAL);  // 'nomodeline'
 
   ftbuf->b_p_ft = xstrdup(filetype);