Update version in change log.

CHANGELOG.md

@@ -8,6 +8,7 @@
         - **.PATCH**: Pull Request Title (PR Author) [PR Number](Link to PR)
 -->
 #### 6.4
+- **.1**: Ensure backward compatibility. v:t_func is not available before Vim 8.0 (Phil Runninger)
 - **.0**: Allow use of function references as callbacks (HiPhish) [#1067](https://github.com/scrooloose/nerdtree/pull/1067)
 #### 6.3
 - **.0**: Add new command that behaves like NERDTreeToggle but defaults to the root of a VCS repository. (willfindlay) [#1060](https://github.com/scrooloose/nerdtree/pull/1060)

lib/nerdtree/key_map.vim

@@ -66,7 +66,7 @@ endfunction
 "FUNCTION: KeyMap.invoke() {{{1
 "Call the KeyMaps callback function
 function! s:KeyMap.invoke(...)
-    let Callback = type(self.callback) == v:t_func ? self.callback : function(self.callback)
+    let Callback = type(self.callback) == type(function("tr")) ? self.callback : function(self.callback)
     if a:0
         call Callback(a:1)
     else

lib/nerdtree/menu_item.vim

@@ -79,7 +79,7 @@ endfunction
 "specified
 function! s:MenuItem.enabled()
     if self.isActiveCallback != -1
-        return type(self.isActiveCallback) == v:t_func ? self.isActiveCallback() : {self.isActiveCallback}()
+        return type(self.isActiveCallback) == type(function("tr")) ? self.isActiveCallback() : {self.isActiveCallback}()
     endif
     return 1
 endfunction
@@ -94,7 +94,7 @@ function! s:MenuItem.execute()
         call mc.showMenu()
     else
         if self.callback != -1
-            if type(self.callback) == v:t_func
+            if type(self.callback) == type(function("tr"))
                 call self.callback()
             else
                 call {self.callback}()

lib/nerdtree/notifier.vim

@@ -15,7 +15,7 @@ function! s:Notifier.NotifyListeners(event, path, nerdtree, params)
     let event = g:NERDTreeEvent.New(a:nerdtree, a:path, a:event, a:params)
 
     for Listener in s:Notifier.GetListenersForEvent(a:event)
-    	let Callback = type(Listener) == v:t_func ? Listener : function(Listener)
+    	let Callback = type(Listener) == type(function("tr")) ? Listener : function(Listener)
         call Callback(event)
     endfor
 endfunction

lib/nerdtree/path.vim

@@ -501,7 +501,7 @@ function! s:Path.ignore(nerdtree)
         endfor
 
         for Callback in g:NERDTree.PathFilters()
-            let Callback = type(Callback) == v:t_func ? Callback : function(Callback)
+            let Callback = type(Callback) == type(function("tr")) ? Callback : function(Callback)
             if Callback({'path': self, 'nerdtree': a:nerdtree})
                 return 1
             endif