[vim] Make arguments to fzf#wrap() optional

fzf#wrap([name string,] [opts dict,] [fullscreen boolean])

README.md

@@ -344,7 +344,7 @@ page](https://github.com/junegunn/fzf/wiki/Examples-(vim)).
 
 #### `fzf#wrap`
 
-`fzf#wrap(name string, [opts dict, [fullscreen boolean]])` is a helper
+`fzf#wrap([name string,] [opts dict,] [fullscreen boolean])` is a helper
 function that decorates the options dictionary so that it understands
 `g:fzf_layout`, `g:fzf_action`, and `g:fzf_history_dir` like `:FZF`.
 

plugin/fzf.vim

@@ -154,13 +154,20 @@ function! s:common_sink(action, lines) abort
   endtry
 endfunction
 
-" name string, [opts dict, [fullscreen boolean]]
-function! fzf#wrap(name, ...)
-  if type(a:name) != type('')
-    throw 'invalid name type: string expected'
-  endif
-  let opts = copy(get(a:000, 0, {}))
-  let bang = get(a:000, 1, 0)
+" [name string,] [opts dict,] [fullscreen boolean]
+function! fzf#wrap(...)
+  let args = ['', {}, 0]
+  let expects = map(copy(args), 'type(v:val)')
+  let tidx = 0
+  for arg in copy(a:000)
+    let tidx = index(expects, type(arg), tidx)
+    if tidx < 0
+      throw 'invalid arguments (expected: [name string] [opts dict] [fullscreen boolean])'
+    endif
+    let args[tidx] = arg
+    let tidx += 1
+  endfor
+  let [name, opts, bang] = args
 
   " Layout: g:fzf_layout (and deprecated g:fzf_height)
   if bang
@@ -179,12 +186,12 @@ function! fzf#wrap(name, ...)
 
   " History: g:fzf_history_dir
   let opts.options = get(opts, 'options', '')
-  if len(get(g:, 'fzf_history_dir', ''))
+  if len(name) && len(get(g:, 'fzf_history_dir', ''))
     let dir = expand(g:fzf_history_dir)
     if !isdirectory(dir)
       call mkdir(dir, 'p')
     endif
-    let opts.options = join(['--history', s:escape(dir.'/'.a:name), opts.options])
+    let opts.options = join(['--history', s:escape(dir.'/'.name), opts.options])
   endif
 
   " Action: g:fzf_action