command/rsync-auto: add --poll flag [GH-4392]

CHANGELOG.md

@@ -19,6 +19,7 @@ IMPROVEMENTS:
   - commands/plugin: Better error output is shown when plugin installation
       fails.
   - commands/reload: show post up messsage [GH-4168]
+  - commands/rsync-auto: Add `--poll` flag. [GH-4392]
   - communicators/winrm: Show stdout/stderr if command fails. [GH-4094]
   - guests/nixos: Added better NFS support. [GH-3983]
   - providers/hyperv: Accept VHD disk format. [GH-4208]

plugins/synced_folders/rsync/command/rsync_auto.rb

@@ -28,9 +28,16 @@ module VagrantPlugins
         def execute
           @logger = Log4r::Logger.new("vagrant::commands::rsync-auto")
 
+          options = {}
           opts = OptionParser.new do |o|
             o.banner = "Usage: vagrant rsync-auto [vm-name]"
             o.separator ""
+            o.separator "Options:"
+            o.separator ""
+
+            o.on("--[no-]poll", "Force polling filesystem (slow)") do |poll|
+              options[:poll] = poll
+            end
           end
 
           # Parse the options and return if we don't have any target.
@@ -106,7 +113,8 @@ module VagrantPlugins
           end
           @logger.info("Listening via: #{Listen::Adapter.select.inspect}")
           callback = method(:callback).to_proc.curry[paths]
-          listener = Listen.to(*paths.keys, ignore: ignores, &callback)
+          listopts = { ignore: ignores, force_polling: !!opts[:poll] }
+          listener = Listen.to(*paths.keys, listopts, &callback)
 
           # Create the callback that lets us know when we've been interrupted
           queue    = Queue.new

website/docs/source/v2/cli/rsync-auto.html.md

@@ -15,6 +15,13 @@ not exit until an interrupt is received.
 The change detection is optimized to use platform-specific APIs to listen
 for filesystem changes, and does not simply poll the directory.
 
+## Options
+
+* `--[no-]poll` - Force Vagrant to watch for changes using filesystem
+    polling instead of filesystem events. This is required for some filesystems
+    that don't support events. Warning: enabling this will make `rsync-auto`
+    _much_ slower. By default, polling is disabled.
+
 ## Machine State Changes
 
 The `rsync-auto` command does not currently handle machine state changes