feat(explorer): add filesystem watchers (#1304)

* feat(explorer): add experimental watchers

This commit introduces watchers to update the tree.
This behavior is introduced behind an "filesystem_watchers" option
which should prevent instabilities.
It will become the default at some point.

Co-authored-by: Alexander Courtis <alex@courtis.org>

lua/nvim-tree/explorer/init.lua

@@ -1,6 +1,7 @@
 local uv = vim.loop
 
 local git = require "nvim-tree.git"
+local watch = require "nvim-tree.explorer.watch"
 
 local M = {}
 
@@ -15,6 +16,8 @@ function Explorer.new(cwd)
   local explorer = setmetatable({
     absolute_path = cwd,
     nodes = {},
+    watcher = watch.create_watcher(cwd),
+    open = true,
   }, Explorer)
   explorer:_load(explorer)
   return explorer
@@ -30,11 +33,30 @@ function Explorer:expand(node)
   self:_load(node)
 end
 
+function Explorer.clear_watchers_for(root_node)
+  local function iterate(node)
+    if node.watcher then
+      node.watcher:stop()
+      for _, child in pairs(node.nodes) do
+        if child.watcher then
+          iterate(child)
+        end
+      end
+    end
+  end
+  iterate(root_node)
+end
+
+function Explorer:_clear_watchers()
+  Explorer.clear_watchers_for(self)
+end
+
 function M.setup(opts)
   require("nvim-tree.explorer.explore").setup(opts)
   require("nvim-tree.explorer.filters").setup(opts)
   require("nvim-tree.explorer.sorters").setup(opts)
   require("nvim-tree.explorer.reload").setup(opts)
+  require("nvim-tree.explorer.watch").setup(opts)
 end
 
 M.Explorer = Explorer