Using NativeManager on Linux, moving a watched directory results in incorrect behavior

[mlacorte]

Description

After moving a directory that hfsnotify is watching, hfsnotify reports changes inside that directory as if it had not been moved.

Only the NativeManager on Linux is affected.

I have not tested the NativeManager on OS X or Windows.

Steps to Reproduce

1. Run the following Bash script:

   mkdir -p /tmp/example

2. Run the following Haskell program:

   {-# LANGUAGE OverloadedStrings #-}
   
   import System.FSNotify
   import Control.Concurrent
   import Control.Monad
   
   main :: IO ()
   main = withManager $ \mgr -> do
     _ <- watchTree mgr "/tmp/example" (const True) print
     forever (threadDelay maxBound)

3. While the Haskell program is running, run the following Bash script:

   cd /tmp/example
   
   mkdir foo
   touch foo/test
   
   mv foo bar
   
   touch bar/test
   rm -rf bar

   Expected Output

Added (FilePath "/tmp/example/foo/test") <TIMESTAMP>
Removed (FilePath "/tmp/example/foo/test") <TIMESTAMP>
Added (FilePath "/tmp/example/bar/test") <TIMESTAMP>
Modified (FilePath "/tmp/example/bar/test") <TIMESTAMP>
Removed (FilePath "/tmp/example/bar/test") <TIMESTAMP>

Actual Output

The following is printed from the Haskell program:

Added (FilePath "/tmp/example/foo/test") <TIMESTAMP>
Modified (FilePath "/tmp/example/foo/test") <TIMESTAMP>
Removed (FilePath "/tmp/example/foo/test") <TIMESTAMP>

[gregwebs]

My guess is that on the whole the behavior around moving a directory that is watched is undefined. We probably need to allow the user to specify whether a directory should be watched after moved, but a possible default that may work cross-platform is to stop watching it.

[thomasjm]

This is just how inotify works--when you move the directory it is moving the inode but it's still watching the same inode.

Solution: we should detect the IN_MOVED_FROM and IN_MOVED_TO events and emit events/update watches accordingly. For example, if a folder is moved outside of a watched tree, we should stop watching it entirely.

[erikd]

Just got hit by a variant on this myself using the conduit version.