Builtin previewer: improve mechanism for backing up/restoring winopts

See :help local-options for more details, but essentially, we have to be
very careful with how we set window-local options on popup windows,
because buffers might take some window-local options from the last
window they were displayed in with them to the new window in certain
circumstances.

This commit changes the backup/restore for the window options so that
the possible window-local options that might get clobbered are saved
from the original active window and reapplied to the preview window just
before it's closed. This ensures any buffers loaded from the picker will
have the same window options applied that were in the active window when
fzf was opened.

lua/fzf-lua/previewer/builtin.lua

@@ -72,11 +72,7 @@ function Previewer:new(o, opts, fzf_win)
 end
 
 function Previewer:close()
-  -- restore winopts backup for those that weren't restored
-  -- (usually the last previewed loaded buffer)
-  for bufnr, _ in pairs(self.backups) do
-    self:restore_winopts(bufnr, self.win.preview_winid)
-  end
+  self:restore_winopts(self.win.preview_winid)
   self:clear_preview_buf()
   self.backups = {}
   _self = nil
@@ -109,31 +105,26 @@ function Previewer:gen_winopts()
     cursorlineopt   = 'both',
     cursorcolumn    = false,
     signcolumn      = 'no',
+    list            = false,
     foldenable      = false,
     foldmethod      = 'manual',
   }
 end
 
-function Previewer:backup_winopts(key, win)
-  if not key then return end
+function Previewer:backup_winopts(win)
   if not win or not api.nvim_win_is_valid(win) then return end
-  self.backups[key] = {}
   for opt, _ in pairs(self:gen_winopts()) do
     if utils.nvim_has_option(opt) then
-      self.backups[key][opt] = api.nvim_win_get_option(win, opt)
+      self.backups[opt] = api.nvim_win_get_option(win, opt)
     end
   end
 end
 
-function Previewer:restore_winopts(key, win)
-  if not self.backups[key] then return end
+function Previewer:restore_winopts(win)
   if not win or not api.nvim_win_is_valid(win) then return end
-  for opt, v in pairs(self.backups[key]) do
-    if utils.nvim_has_option(opt) then
-      api.nvim_win_set_option(win, opt, v)
+    for opt, value in pairs(self.backups) do
+      vim.api.nvim_win_set_option(win, opt, value)
     end
-  end
-  self.backups[key] = nil
 end
 
 function Previewer:set_winopts(win)
@@ -269,10 +260,8 @@ function Previewer:display_last_entry()
 end
 
 function Previewer:preview_buf_post(entry)
-  -- backup window options
   local bufnr = self.preview_bufnr
   local preview_winid = self.win.preview_winid
-  self:backup_winopts(bufnr, preview_winid)
 
   -- set preview win options or load the file
   -- if not already loaded from buffer
@@ -308,11 +297,12 @@ function Previewer:display_entry(entry)
     self.last_entry = entry
   end
   if not self.win or not self.win:validate_preview() then return end
+  if rawequal(next(self.backups), nil) then
+      self:backup_winopts(self.win.src_winid)
+  end
   local preview_winid = self.win.preview_winid
   local previous_bufnr = api.nvim_win_get_buf(preview_winid)
   assert(not self.preview_bufnr or previous_bufnr == self.preview_bufnr)
-  -- restore settings for the buffer we were previously viewing
-  self:restore_winopts(previous_bufnr, preview_winid)
   -- clear the current preview buffer
   local bufnr = self:clear_preview_buf()
   -- store the preview buffer

lua/fzf-lua/win.lua

@@ -387,6 +387,7 @@ function FzfWin:create()
   -- save sending bufnr/winid
   self.src_bufnr = vim.api.nvim_get_current_buf()
   self.src_winid = vim.api.nvim_get_current_win()
+
   if self.winopts.split then
     vim.cmd(self.winopts.split)
     self.fzf_bufnr = vim.api.nvim_get_current_buf()