fix(ui_select): align upstream opts.preview_items spec

lua/fzf-lua/previewer/builtin.lua

@@ -959,6 +959,11 @@ function Previewer.buffer_or_file:populate_preview_buf(entry_str)
   -- kill previously running jobs
   self:_stop_preview_job()
 
+  if entry._scratch_buf then
+    self:set_preview_buf(entry._scratch_buf)
+    self:preview_buf_post(entry)
+    return
+  end
   -- check if cached is update-to-date to be reuse
   local cached, stale = self.bcache:check(entry)
   entry.cached = cached

lua/fzf-lua/providers/ui_select.lua

@@ -181,7 +181,17 @@ M.ui_select = function(items, ui_opts, on_choice)
       _ctor = function()
         local previewer = require("fzf-lua.previewer.builtin").buffer_or_file:extend()
         ---@diagnostic disable-next-line: unused
-        function previewer:parse_entry(entry_str, cb) return ui_opts.preview_item(entry_str, cb) end
+        function previewer:parse_entry(entry_str, cb)
+          local res = assert(ui_opts.preview_item(entry_str, cb))
+          local pos_start, pos_end = res.pos, res.pos_end
+          return {
+            _scratch_buf = res.buf,
+            line = pos_start and pos_start[1] or 1,
+            col = pos_start and pos_start[2] or 1,
+            end_line = pos_end and pos_end[1] or 1,
+            end_col = pos_end and pos_end[2] or 1,
+          }
+        end
 
         return previewer
       end

lua/fzf-lua/types.lua

@@ -39,6 +39,7 @@ local FzfLua = require("fzf-lua")
 ---@field end_col? integer 1-based
 ---@field open_term? boolean open_term for content (cmd always open_term)
 ---@field cache_key? any unique cache key for entry (to reuse preview buffer)
+---@field _scratch_buf? integer "unmanaged" buffer
 
 ---@class fzf-lua.keymap.Entry: fzf-lua.buffer_or_file.Entry
 ---@field vmap string?