Lazy Directory Refresh

doc/NERDTree.txt

@@ -774,6 +774,8 @@ the NERDTree. These settings should be set in your vimrc, using `:let`.
 |NERDTreeCustomOpenArgs|      A dictionary with values that control how a node
                             is opened with the |NERDTree-<CR>| key.
 
+|NERDTreeLazyDirRefresh|      Enables lazy directory refreshing (experimental)
+
 ------------------------------------------------------------------------------
 3.2. Customisation details                             *NERDTreeSettingsDetails*
 
@@ -1311,6 +1313,18 @@ To open files and directories (creating a new NERDTree) in a new tab, >
 <
 To open a file always in the current tab, and expand directories in place, >
     {'file': {'reuse':'currenttab', 'where':'p', 'keepopen':1, 'stay':1}}
+<
+------------------------------------------------------------------------------
+                                                        *NERDTreeLazyDirRefresh*
+Values: 0 or 1
+Default: 0
+
+'experimental'
+
+If set to 1, the NERDTree will use lazy refresh on close directories whenever
+a refresh action is performed. Actual refresh happens when it is required.
+It happens on directory open and findNode functions.
+
 <
 ==============================================================================
 4. The NERDTree API                                                *NERDTreeAPI*

lib/nerdtree/tree_dir_node.vim

@@ -118,6 +118,7 @@ endfunction
 " path: a path object
 unlet s:TreeDirNode.findNode
 function! s:TreeDirNode.findNode(path)
+    call self.refresh(2)
     if a:path.equals(self.path)
         return self
     endif
@@ -461,6 +462,8 @@ function! s:TreeDirNode.New(path, nerdtree)
     let newTreeNode.isOpen = 0
     let newTreeNode.children = []
 
+    let newTreeNode.lazyRefresh = 0
+
     let newTreeNode.parent = {}
     let newTreeNode._nerdtree = a:nerdtree
 
@@ -472,6 +475,7 @@ endfunction
 " are provided. Return 0 if options were processed. Otherwise, return the
 " number of new cached nodes.
 function! s:TreeDirNode.open(...)
+    call self.refresh(2)
     let l:options = a:0 ? a:1 : {}
 
     " If special options were specified, process them and return.
@@ -557,12 +561,24 @@ function! s:TreeDirNode.openRecursively()
     endfor
 endfunction
 
-" FUNCTION: TreeDirNode.refresh() {{{1
-function! s:TreeDirNode.refresh()
+" FUNCTION: TreeDirNode.refresh([options]) {{{1
+" refreshes the node and its children
+"
+" Args:
+" An optional integer selecting refresh mode
+"
+" 0 == normal (default)
+" 1 == force
+" 2 == lazyRefresh (refreshes node only if lazyRefresh flag is set)
+"
+function! s:TreeDirNode.refresh(...)
+    let l:mode = a:0 ? a:1 : 0
     call self.path.refresh(self.getNerdtree())
 
-    "if this node was ever opened, refresh its children
-    if self.isOpen || !empty(self.children)
+    "if refresh is forced, refresh its children
+    "if this node is open, refresh its children
+    "if this node is flaged for lazyRefresh and lazyRefresh requested, refresh its children
+    if l:mode == 1 || self.isOpen || (!empty(self.children) && !g:NERDTreeLazyDirRefresh) || (l:mode == 2 && self.lazyRefresh)
         let files = self._glob('*', 1) + self._glob('.*', 0)
         let newChildNodes = []
         let invalidFilesFound = 0
@@ -595,6 +611,10 @@ function! s:TreeDirNode.refresh()
         if invalidFilesFound
             call nerdtree#echoWarning(invalidFilesFound . ' Invalid file(s): ' . join(invalidFiles, ', '))
         endif
+        let self.lazyRefresh = 0
+    " if this node is not empty and NERDTreeLazyDirRefresh is enable flag the node for lazyRefresh
+    elseif g:NERDTreeLazyDirRefresh && !empty(self.children)
+        let self.lazyRefresh = 1
     endif
 endfunction
 

plugin/NERD_tree.vim

@@ -52,6 +52,7 @@ let g:NERDTreeShowFiles             = get(g:, 'NERDTreeShowFiles',             1
 let g:NERDTreeShowHidden            = get(g:, 'NERDTreeShowHidden',            0)
 let g:NERDTreeShowLineNumbers       = get(g:, 'NERDTreeShowLineNumbers',       0)
 let g:NERDTreeSortDirs              = get(g:, 'NERDTreeSortDirs',              1)
+let g:NERDTreeLazyDirRefresh        = get(g:, 'NERDTreeLazyDirRefresh',        0)
 
 if !nerdtree#runningWindows() && !nerdtree#runningCygwin()
     let g:NERDTreeDirArrowExpandable  = get(g:, 'NERDTreeDirArrowExpandable',  '▸')