fix: use win_execute()

* The current implementation of `s:WinDo()` fails at avoiding some side
  effects. Specifically, `:windo` and `:wincmd w` trigger `CursorMoved`
  even if `noautocmd` is used (both in Vim and Nvim ≥ 0.10). So use
  `win_execute()` if it's available.
* With `win_execute()`, setting fdm itself doesn't seem to trigger
  recomputation of fold. Querying the foldlevel seems to be sufficient
  for triggerring fold recomputation.

Author: tomtomjhj

plugin/fastfold.vim

@@ -68,33 +68,42 @@ function! s:LeaveWin()
   endif
 endfunction
 
-" Like windo but restore the current buffer.
-" See http://vim.wikia.com/wiki/Run_a_command_in_multiple_buffers#Restoring_position
-function! s:WinDo( command )
-  " avoid errors in CmdWin
-  if exists('*getcmdwintype') && !empty(getcmdwintype())
-    return
-  endif
-  " Work around Vim bug.
-  " See https://groups.google.com/forum/#!topic/vim_dev/LLTw8JV6wKg
-  let curaltwin = winnr('#') ? winnr('#') : 1
-  let currwin=winnr()
-  if &scrollopt =~# '\<jump\>'
-    set scrollopt-=jump
-    let l:restore = 'set scrollopt+=jump'
-  endif
-  " Work around Vim bug.
-  " See https://github.com/vim/vim/issues/4622#issuecomment-508985573
-  let l:currwinwidth = &winwidth
-  let &winwidth = &winminwidth > 0 ? &winminwidth : 1
-  silent! execute 'keepjumps noautocmd windo ' . a:command
-  silent! execute 'noautocmd ' . curaltwin . 'wincmd w'
-  silent! execute 'noautocmd ' . currwin . 'wincmd w'
-  if exists('l:restore')
-    exe l:restore
-  endif
-  let &winwidth = l:currwinwidth
-endfunction
+" Like :windo, but restores the current window and avoids side effects.
+if exists('*win_execute')
+  function! s:WinDo( command )
+    for w in range(1, winnr('$'))
+      " query foldlevel to trigger recomputation of folds
+      call win_execute(win_getid(w), a:command . ' | if !s:Skip() | call foldlevel(1) | endif', 'silent!')
+    endfor
+  endfunction
+else
+  " See http://vim.wikia.com/wiki/Run_a_command_in_multiple_buffers#Restoring_position
+  function! s:WinDo( command )
+    " avoid errors in CmdWin
+    if exists('*getcmdwintype') && !empty(getcmdwintype())
+      return
+    endif
+    " Work around Vim bug.
+    " See https://groups.google.com/forum/#!topic/vim_dev/LLTw8JV6wKg
+    let curaltwin = winnr('#') ? winnr('#') : 1
+    let currwin=winnr()
+    if &scrollopt =~# '\<jump\>'
+      set scrollopt-=jump
+      let l:restore = 'set scrollopt+=jump'
+    endif
+    " Work around Vim bug.
+    " See https://github.com/vim/vim/issues/4622#issuecomment-508985573
+    let l:currwinwidth = &winwidth
+    let &winwidth = &winminwidth > 0 ? &winminwidth : 1
+    silent! execute 'keepjumps noautocmd windo ' . a:command
+    silent! execute 'noautocmd ' . curaltwin . 'wincmd w'
+    silent! execute 'noautocmd ' . currwin . 'wincmd w'
+    if exists('l:restore')
+      exe l:restore
+    endif
+    let &winwidth = l:currwinwidth
+  endfunction
+endif
 
 " WinEnter then TabEnter then BufEnter then BufWinEnter
 function! s:UpdateWin()