feat - add open and close tree events (#1151)

doc/nvim-tree-lua.txt

@@ -988,6 +988,22 @@ on_folder_created({handler})
 on_folder_removed({handler})
                 Registers a handler for when a folder is removed.
 
+                Parameters: ~
+                    {handler}    (function) Handler function, with the
+                                 signature `function(payload)`.
+
+                                   *nvim-tree.events.on_tree_open()*
+on_tree_open({handler})
+                Registers a handler for when NvimTree is opened.
+
+                Parameters: ~
+                    {handler}    (function) Handler function, with the
+                                 signature `function(payload)`.
+
+                                   *nvim-tree.events.on_tree_close()*
+on_tree_close({handler})
+                Registers a handler for when NvimTree is closed.
+
                 Parameters: ~
                     {handler}    (function) Handler function, with the
                                  signature `function(payload)`.

lua/nvim-tree/events.lua

@@ -5,6 +5,8 @@ local global_handlers = {}
 local Event = {
   Ready = "Ready",
   NodeRenamed = "NodeRenamed",
+  TreeOpen = "TreeOpen",
+  TreeClose = "TreeClose",
   FileCreated = "FileCreated",
   FileRemoved = "FileRemoved",
   FolderCreated = "FolderCreated",
@@ -60,6 +62,16 @@ function M._dispatch_folder_removed(folder_name)
   dispatch(Event.FolderRemoved, { folder_name = folder_name })
 end
 
+--@private
+function M._dispatch_on_tree_open()
+  dispatch(Event.TreeOpen, nil)
+end
+
+--@private
+function M._dispatch_on_tree_close()
+  dispatch(Event.TreeClose, nil)
+end
+
 --Registers a handler for the Ready event.
 --@param handler (function) Handler with the signature `function()`
 function M.on_nvim_tree_ready(handler)
@@ -102,4 +114,16 @@ function M.on_folder_removed(handler)
   register_handler(Event.FolderRemoved, handler)
 end
 
+--Registers a handler for the TreeOpen event.
+--@param handler (function) Handler with the signature function(payload)
+function M.on_tree_open(handler)
+  register_handler(Event.TreeOpen, handler)
+end
+
+--Registers a handler for the TreeClose event.
+--@param handler (function) Handler with the signature function(payload)
+function M.on_tree_close(handler)
+  register_handler(Event.TreeClose, handler)
+end
+
 return M

lua/nvim-tree/view.lua

@@ -2,6 +2,8 @@ local a = vim.api
 
 local M = {}
 
+local events = require "nvim-tree.events"
+
 M.View = {
   tabpages = {},
   hide_root_folder = false,
@@ -173,6 +175,7 @@ function M.close()
       if tree_win == current_win and LAST_FOCUSED_WIN then
         a.nvim_set_current_win(LAST_FOCUSED_WIN)
       end
+      events._dispatch_on_tree_close()
       return
     end
   end
@@ -193,6 +196,7 @@ function M.open(options)
   if not opts.focus_tree then
     vim.cmd "wincmd p"
   end
+  events._dispatch_on_tree_open()
 end
 
 function M.resize(size)