Add a NERDTreeCWD command to change tree root to CWD

doc/NERD_tree.txt

@@ -137,6 +137,10 @@ The following features and functionality are provided by the NERD tree:
 
     In any case, the current file is revealed and the cursor is placed on it.
 
+:NERDTreeCWD                                                    *:NERDTreeCWD*
+    Change tree root to current directory. If no NERD tree exists for this
+    tab, a new tree will be opened.
+
 ------------------------------------------------------------------------------
 2.2. Bookmarks                                             *NERDTreeBookmarks*
 
@@ -247,6 +251,7 @@ r.......Recursively refresh the current directory................|NERDTree-r|
 R.......Recursively refresh the current root.....................|NERDTree-R|
 m.......Display the NERD tree menu...............................|NERDTree-m|
 cd......Change the CWD to the dir of the selected node...........|NERDTree-cd|
+CD......Change tree root to the CWD..............................|NERDTree-CD|
 
 I.......Toggle whether hidden files displayed....................|NERDTree-I|
 f.......Toggle whether the file filters are used.................|NERDTree-f|
@@ -514,6 +519,14 @@ Applies to: files and directories.
 
 Change vims current working directory to that of the selected node.
 
+------------------------------------------------------------------------------
+                                                                 *NERDTree-CD*
+Default key: CD
+Map option: NERDTreeMapCWD
+Applies to: no restrictions.
+
+Change tree root to vims current working directory.
+
 ------------------------------------------------------------------------------
                                                                   *NERDTree-I*
 Default key: I

plugin/NERD_tree.vim

@@ -140,6 +140,7 @@ call s:initVariable("g:NERDTreeMapToggleHidden", "I")
 call s:initVariable("g:NERDTreeMapToggleZoom", "A")
 call s:initVariable("g:NERDTreeMapUpdir", "u")
 call s:initVariable("g:NERDTreeMapUpdirKeepOpen", "U")
+call s:initVariable("g:NERDTreeMapCWD", "CD")
 
 "SECTION: Script level variable declaration{{{2
 if s:running_windows
@@ -171,6 +172,7 @@ command! -n=1 -complete=customlist,s:completeBookmarks -bar NERDTreeFromBookmark
 command! -n=0 -bar NERDTreeMirror call s:initNerdTreeMirror()
 command! -n=0 -bar NERDTreeFind call s:findAndRevealPath()
 command! -n=0 -bar NERDTreeFocus call NERDTreeFocus()
+command! -n=0 -bar NERDTreeCWD call NERDTreeCWD()
 " SECTION: Auto commands {{{1
 "============================================================
 augroup NERDTree
@@ -2936,6 +2938,8 @@ function! s:createDefaultBindings()
 
     call NERDTreeAddKeyMap({ 'key': g:NERDTreeMapQuit, 'scope': "all", 'callback': s."closeTreeWindow" })
 
+    call NERDTreeAddKeyMap({ 'key': g:NERDTreeMapCWD, 'scope': "all", 'callback': s."chRootCwd" })
+
     call NERDTreeAddKeyMap({ 'key': g:NERDTreeMapRefreshRoot, 'scope': "all", 'callback': s."refreshRoot" })
     call NERDTreeAddKeyMap({ 'key': g:NERDTreeMapRefresh, 'scope': "Node", 'callback': s."refreshCurrent" })
 
@@ -3305,6 +3309,11 @@ function! NERDTreeFocus()
     endif
 endfunction
 
+function! NERDTreeCWD()
+    call NERDTreeFocus()
+    call s:chRootCwd()
+endfunction
+
 " SECTION: View Functions {{{1
 "============================================================
 "FUNCTION: s:centerView() {{{2
@@ -3445,6 +3454,7 @@ function! s:dumpHelp()
         let @h=@h."\" ". g:NERDTreeMapMenu .": Show menu\n"
         let @h=@h."\" ". g:NERDTreeMapChdir .":change the CWD to the\n"
         let @h=@h."\"    selected dir\n"
+        let @h=@h."\" ". g:NERDTreeMapCWD .":change tree root to CWD\n"
 
         let @h=@h."\"\n\" ----------------------------\n"
         let @h=@h."\" Tree filtering mappings~\n"
@@ -4055,6 +4065,21 @@ function! s:chRoot(node)
     call b:NERDTreeRoot.putCursorHere(0, 0)
 endfunction
 
+" FUNCTION: s:chRootCwd() {{{2
+" changes the current root to CWD
+function! s:chRootCwd()
+    try
+        let cwd = s:Path.New(getcwd())
+    catch /^NERDTree.InvalidArgumentsError/
+        call s:echo("current directory does not exist.")
+        return
+    endtry
+    if cwd.str() == s:TreeFileNode.GetRootForTab().path.str()
+       return
+    endif
+    call s:chRoot(s:TreeDirNode.New(cwd))
+endfunction
+
 " FUNCTION: s:clearBookmarks(bookmarks) {{{2
 function! s:clearBookmarks(bookmarks)
     if a:bookmarks ==# ''