nvim-tree.lua/lua/nvim-tree/watcher.lua

local notify = require("nvim-tree.notify")
local log = require("nvim-tree.log")
local utils = require("nvim-tree.utils")

local M = {
  config = {},
}

---@class Event
local Event = {
  _events = {},
}
Event.__index = Event

---@class Watcher
local Watcher = {
  _watchers = {},
}
Watcher.__index = Watcher

local FS_EVENT_FLAGS = {
  -- inotify or equivalent will be used; fallback to stat has not yet been implemented
  stat = false,
  -- recursive is not functional in neovim's libuv implementation
  recursive = false,
}

---@param path string
---@return Event|nil
function Event:new(path)
  log.line("watcher", "Event:new '%s'", path)

  local e = setmetatable({
    _path = path,
    _fs_event = nil,
    _listeners = {},
  }, Event)

  if e:start() then
    Event._events[path] = e
    return e
  else
    return nil
  end
end

---@return boolean
function Event:start()
  log.line("watcher", "Event:start '%s'", self._path)

  local rc, _, name

  self._fs_event, _, name = vim.loop.new_fs_event()
  if not self._fs_event then
    self._fs_event = nil
    notify.warn(string.format("Could not initialize an fs_event watcher for path %s : %s", self._path, name))
    return false
  end

  local event_cb = vim.schedule_wrap(function(err, filename)
    if err then
      log.line("watcher", "event_cb '%s' '%s' FAIL : %s", self._path, filename, err)
      local message = string.format("File system watcher failed (%s) for path %s, halting watcher.", err, self._path)
      if err == "EPERM" and (utils.is_windows or utils.is_wsl) then
        -- on directory removal windows will cascade the filesystem events out of order
        log.line("watcher", message)
        self:destroy()
      else
        self:destroy(message)
      end
    else
      log.line("watcher", "event_cb '%s' '%s'", self._path, filename)
      for _, listener in ipairs(self._listeners) do
        listener(filename)
      end
    end
  end)

  rc, _, name = self._fs_event:start(self._path, FS_EVENT_FLAGS, event_cb)
  if rc ~= 0 then
    if name == "EMFILE" then
      M.disable_watchers("fs.inotify.max_user_watches exceeded, see https://github.com/nvim-tree/nvim-tree.lua/wiki/Troubleshooting")
    else
      notify.warn(string.format("Could not start the fs_event watcher for path %s : %s", self._path, name))
    end
    return false
  end

  return true
end

---@param listener function
function Event:add(listener)
  table.insert(self._listeners, listener)
end

---@param listener function
function Event:remove(listener)
  utils.array_remove(self._listeners, listener)
  if #self._listeners == 0 then
    self:destroy()
  end
end

---@param message string|nil
function Event:destroy(message)
  log.line("watcher", "Event:destroy '%s'", self._path)

  if self._fs_event then
    if message then
      notify.warn(message)
    end

    local rc, _, name = self._fs_event:stop()
    if rc ~= 0 then
      notify.warn(string.format("Could not stop the fs_event watcher for path %s : %s", self._path, name))
    end
    self._fs_event = nil
  end

  Event._events[self._path] = nil

  self.destroyed = true
end

---@param path string
---@param files string[]|nil
---@param callback function
---@param data table
---@return Watcher|nil
function Watcher:new(path, files, callback, data)
  log.line("watcher", "Watcher:new '%s' %s", path, vim.inspect(files))

  local w = setmetatable(data, Watcher)

  w._event = Event._events[path] or Event:new(path)
  w._listener = nil
  w._path = path
  w._files = files
  w._callback = callback

  if not w._event then
    return nil
  end

  w:start()

  table.insert(Watcher._watchers, w)

  return w
end

function Watcher:start()
  self._listener = function(filename)
    if not self._files or vim.tbl_contains(self._files, filename) then
      self._callback(self)
    end
  end

  self._event:add(self._listener)
end

function Watcher:destroy()
  log.line("watcher", "Watcher:destroy '%s'", self._path)

  self._event:remove(self._listener)

  utils.array_remove(Watcher._watchers, self)

  self.destroyed = true
end

M.Watcher = Watcher

--- Permanently disable watchers and purge all state following a catastrophic error.
---@param msg string
function M.disable_watchers(msg)
  notify.warn(string.format("Disabling watchers: %s", msg))
  M.config.filesystem_watchers.enable = false
  require("nvim-tree").purge_all_state()
end

function M.purge_watchers()
  log.line("watcher", "purge_watchers")

  for _, w in ipairs(utils.array_shallow_clone(Watcher._watchers)) do
    w:destroy()
  end

  for _, e in pairs(Event._events) do
    e:destroy()
  end
end

--- Windows NT will present directories that cannot be enumerated.
--- Detect these by attempting to start an event monitor.
---@param path string
---@return boolean
function M.is_fs_event_capable(path)
  if not utils.is_windows then
    return true
  end

  local fs_event = vim.loop.new_fs_event()
  if not fs_event then
    return false
  end

  if fs_event:start(path, FS_EVENT_FLAGS, function() end) ~= 0 then
    return false
  end

  if fs_event:stop() ~= 0 then
    return false
  end

  return true
end

function M.setup(opts)
  M.config.filesystem_watchers = opts.filesystem_watchers
end

return M