perf: avoid copying buffer/window variables to lua

Problem:
Calling vim.fn.{getbufinfo,getwininfo} in lua can be slow because it has
to convert potentially big and cyclic data structures stored in vim
buffer/window variables into lua values.

Solution:
Remove buffer/window variables from the result before passing it to lua.

autoload/fzf_lua.vim

@@ -0,0 +1,22 @@
+" Calling vim.fn.getbufinfo in lua can be expensive because it has to convert
+" all the buffer variables into lua values. Since fzf-lua does not access
+" buffer variables, this cost can be avoided by clearing the entry before
+" passing the info to lua.
+function! fzf_lua#getbufinfo(bufnr) abort
+  let info = getbufinfo(a:bufnr)
+  if empty(info)
+    return v:false " there is no way to return `nil` from vimscript
+  endif
+  unlet! info[0].variables
+  return info[0]
+endfunction
+
+" Similar to fzf_lua#getbufinfo, but for getwininfo.
+function! fzf_lua#getwininfo(winid) abort
+  let info = getwininfo(a:winid)
+  if empty(info)
+    return v:false
+  endif
+  unlet! info[0].variables
+  return info[0]
+endfunction

lua/fzf-lua/previewer/builtin.lua

@@ -108,7 +108,7 @@ end
 
 function Previewer.base:preview_is_terminal()
   if not self.win or not self.win:validate_preview() then return end
-  return vim.fn.getwininfo(self.win.preview_winid)[1].terminal == 1
+  return vim.fn["fzf_lua#getwininfo"](self.win.preview_winid).terminal == 1
 end
 
 function Previewer.base:get_tmp_buffer()
@@ -368,10 +368,10 @@ function Previewer.base:scroll(direction)
   -- user scrolls, the highlight is no longer relevant (#462).
   -- Conditionally toggle 'cursorline' based on cursor position
   if self.orig_pos and self.winopts.cursorline then
-    local wininfo = vim.fn.getwininfo(preview_winid)
-    if wininfo and wininfo[1] and
-        self.orig_pos[1] >= wininfo[1].topline and
-        self.orig_pos[1] <= wininfo[1].botline then
+    local wininfo = vim.fn["fzf_lua#getwininfo"](preview_winid)
+    if wininfo and
+        self.orig_pos[1] >= wininfo.topline and
+        self.orig_pos[1] <= wininfo.botline then
       -- reset cursor pos even when it's already there, no bigggie
       -- local curpos = vim.api.nvim_win_get_cursor(preview_winid)
       vim.api.nvim_win_set_cursor(preview_winid, self.orig_pos)

lua/fzf-lua/providers/buffers.lua

@@ -67,7 +67,7 @@ local populate_buffer_entries = function(opts, bufnrs, tabh)
     local element = {
       bufnr = bufnr,
       flag = flag,
-      info = vim.fn.getbufinfo(bufnr)[1],
+      info = vim.fn["fzf_lua#getbufinfo"](bufnr),
       readonly = vim.bo[bufnr].readonly
     }
 

lua/fzf-lua/utils.lua

@@ -805,17 +805,17 @@ function M.is_term_buffer(bufnr)
   bufnr = bufnr == 0 and vim.api.nvim_get_current_buf() or bufnr
   local winid = vim.fn.bufwinid(bufnr)
   if tonumber(winid) > 0 and vim.api.nvim_win_is_valid(winid) then
-    return vim.fn.getwininfo(winid)[1].terminal == 1
+    return vim.fn["fzf_lua#getwininfo"](winid).terminal == 1
   end
   local bufname = vim.api.nvim_buf_is_valid(bufnr) and vim.api.nvim_buf_get_name(bufnr)
   return M.is_term_bufname(bufname)
 end
 
 function M.buffer_is_dirty(bufnr, warn, only_if_last_buffer)
   bufnr = tonumber(bufnr) or vim.api.nvim_get_current_buf()
-  local info = bufnr and vim.fn.getbufinfo(bufnr)[1]
+  local info = bufnr and vim.fn["fzf_lua#getbufinfo"](bufnr)
   if info and info.changed ~= 0 then
-    if only_if_last_buffer and 1 < M.tbl_length(vim.fn.win_findbuf(bufnr)) then
+    if only_if_last_buffer and 1 < #vim.fn.win_findbuf(bufnr) then
       return false
     end
     if warn then
@@ -829,7 +829,7 @@ end
 
 function M.save_dialog(bufnr)
   bufnr = tonumber(bufnr) or vim.api.nvim_get_current_buf()
-  local info = bufnr and vim.fn.getbufinfo(bufnr)[1]
+  local info = bufnr and vim.fn["fzf_lua#getbufinfo"](bufnr)
   if not info.name or #info.name == 0 then
     -- unnamed buffers can't be saved
     M.warn(string.format("buffer %d has unsaved changes", bufnr))
@@ -854,7 +854,7 @@ end
 --   2 for loc list
 function M.win_is_qf(winid, wininfo)
   wininfo = wininfo or
-      (vim.api.nvim_win_is_valid(winid) and vim.fn.getwininfo(winid)[1])
+      (vim.api.nvim_win_is_valid(winid) and vim.fn["fzf_lua#getwininfo"](winid))
   if wininfo and wininfo.quickfix == 1 then
     return wininfo.loclist == 1 and 2 or 1
   end
@@ -863,7 +863,7 @@ end
 
 function M.buf_is_qf(bufnr, bufinfo)
   bufinfo = bufinfo or
-      (vim.api.nvim_buf_is_valid(bufnr) and vim.fn.getbufinfo(bufnr)[1])
+      (vim.api.nvim_buf_is_valid(bufnr) and vim.fn["fzf_lua#getbufinfo"](bufnr))
   if bufinfo and bufinfo.variables and
       bufinfo.variables.current_syntax == "qf" and
       not vim.tbl_isempty(bufinfo.windows) then

lua/fzf-lua/win.lua

@@ -466,7 +466,7 @@ end
 
 function FzfWin:preview_layout()
   if self.winopts.split and self.previewer_is_builtin then
-    local wininfo = fn.getwininfo(self.fzf_winid)[1]
+    local wininfo = fn["fzf_lua#getwininfo"](self.fzf_winid)
     -- unlike floating win popups, split windows inherit the global
     -- 'signcolumn' setting which affects the available width for fzf
     -- 'generate_layout' will then use the sign column available width
@@ -1144,7 +1144,7 @@ function FzfWin:update_scrollbar(hide)
   local buf = api.nvim_win_get_buf(self.preview_winid)
 
   local o = {}
-  o.wininfo = fn.getwininfo(self.preview_winid)[1]
+  o.wininfo = fn["fzf_lua#getwininfo"](self.preview_winid)
   o.line_count = api.nvim_buf_line_count(buf)
 
   local topline, height = o.wininfo.topline, o.wininfo.height