[vim] Fix directory switching around sink function

Close #1356

Related:
- #612
- https://github.com/junegunn/fzf.vim/issues/308

plugin/fzf.vim

@@ -357,7 +357,7 @@ try
     throw v:exception
   endtry
 
-  if has('nvim') && !has_key(dict, 'dir')
+  if !has_key(dict, 'dir')
     let dict.dir = s:fzf_getcwd()
   endif
   if has('win32unix') && has_key(dict, 'dir')
@@ -477,7 +477,25 @@ function! s:dopopd()
   if !exists('w:fzf_pushd')
     return
   endif
-  execute w:fzf_pushd.command s:escape(w:fzf_pushd.origin)
+
+  " FIXME: We temporarily change the working directory to 'dir' entry
+  " of options dictionary (set to the current working directory if not given)
+  " before running fzf.
+  "
+  " e.g. call fzf#run({'dir': '/tmp', 'source': 'ls', 'sink': 'e'})
+  "
+  " After processing the sink function, we have to restore the current working
+  " directory. But doing so may not be desirable if the function changed the
+  " working directory on purpose.
+  "
+  " So how can we tell if we should do it or not? A simple heuristic we use
+  " here is that we change directory only if the current working directory
+  " matches 'dir' entry. However, it is possible that the sink function did
+  " change the directory to 'dir'. In that case, the user will have an
+  " unexpected result.
+  if s:fzf_getcwd() ==# w:fzf_pushd.dir
+    execute w:fzf_pushd.command s:escape(w:fzf_pushd.origin)
+  endif
   unlet w:fzf_pushd
 endfunction
 
@@ -724,19 +742,7 @@ function! s:collect(temps) abort
 endfunction
 
 function! s:callback(dict, lines) abort
-  " Since anything can be done in the sink function, there is no telling that
-  " the change of the working directory was made by &autochdir setting.
-  "
-  " We use the following heuristic to determine whether to restore CWD:
-  " - Always restore the current directory when &autochdir is disabled.
-  "   FIXME This makes it impossible to change directory from inside the sink
-  "   function when &autochdir is not used.
-  " - In case of an error or an interrupt, a:lines will be empty.
-  "   And it will be an array of a single empty string when fzf was finished
-  "   without a match. In these cases, we presume that the change of the
-  "   directory is not expected and should be undone.
-  let popd = has_key(a:dict, 'pushd') &&
-        \ (!&autochdir || (empty(a:lines) || len(a:lines) == 1 && empty(a:lines[0])))
+  let popd = has_key(a:dict, 'pushd')
   if popd
     let w:fzf_pushd = a:dict.pushd
   endif