[vim] Add g:Fzf_launcher for funcrefs (#212)

README.md

@@ -294,7 +294,8 @@ of the selected items.
 | `dir`                      | string        | Working directory                                                |
 | `up`/`down`/`left`/`right` | number/string | Use tmux pane with the given size (e.g. `20`, `50%`)             |
 | `window` (*Neovim only*)   | string        | Command to open fzf window (e.g. `vertical aboveleft 30new`)     |
-| `launcher`                 | string        | External terminal emulator to start fzf with (Only used in GVim) |
+| `launcher`                 | string        | External terminal emulator to start fzf with (GVim only)         |
+| `launcher`                 | funcref       | Function for generating `launcher` string (GVim only)            |
 
 _However on Neovim `fzf#run` is asynchronous and does not return values so you
 should use `sink` or `sink*` to process the output from fzf._

plugin/fzf.vim

@@ -206,8 +206,9 @@ function! s:execute(dict, command, temps)
   call s:pushd(a:dict)
   silent! !clear 2> /dev/null
   if has('gui_running')
-    let launcher = get(a:dict, 'launcher', get(g:, 'fzf_launcher', s:launcher))
-    let command = printf(launcher, "'".substitute(a:command, "'", "'\"'\"'", 'g')."'")
+    let Launcher = get(a:dict, 'launcher', get(g:, 'Fzf_launcher', get(g:, 'fzf_launcher', s:launcher)))
+    let fmt = type(Launcher) == 2 ? call(Launcher, []) : Launcher
+    let command = printf(fmt, "'".substitute(a:command, "'", "'\"'\"'", 'g')."'")
   else
     let command = a:command
   endif