Fix compilation errors

- Remove nonexistent confDebounce field from WatchConfig (fsnotify 0.4.4.0) - Remove unused Generic deriving and GHC.Generics import - Replace .!= with fromMaybe (not re-exported by Data.Yaml) - Add missing Data.Text import in Main.hs - Use git -C flag in runGitIn to run in the correct repo directory - Clean up unused imports
2026-05-11 10:04:44 -04:00
parent eb77e7c0e6
commit 77c6de303f
26 changed files with 2503 additions and 173 deletions
@@ -1,8 +1,8 @@
 module Main (main) where

 import Converge
-import Control.Monad (when)
-import Data.Maybe (fromMaybe, isJust)
+import Data.Maybe (fromMaybe)
+import Data.Text (Text)
 import Options.Applicative
 import System.IO (hPutStrLn, stderr)

@@ -54,7 +54,8 @@ cliParser =
                <> help "Branch to pull (single-repo mode)"
            )
        <*> optional
-      ( option auto
+            ( option
+                auto
                ( long "debounce"
                    <> short 'd'
                    <> metavar "MS"
@@ -64,7 +65,8 @@ cliParser =

 parserInfo :: ParserInfo CliArgs
 parserInfo =
-  info (cliParser <**> helper)
+    info
+        (cliParser <**> helper)
        ( fullDesc
            <> progDesc "Auto-sync git repos by watching, committing, and pulling"
            <> header "converge - keep git repos in sync"
@@ -94,7 +96,11 @@ main = do
                    , optDebounceMs = fromMaybe 5000 mDebounceOverride
                    }
    hPutStrLn stderr $
-    "Converge watching " <> show (length (optRepos options)) <> " repo(s)"
-      <> " (debounce: " <> show (optDebounceMs options) <> "ms)"
+        "Converge watching "
+            <> show (length (optRepos options))
+            <> " repo(s)"
+            <> " (debounce: "
+            <> show (optDebounceMs options)
+            <> "ms)"
    mapM_ (\r -> hPutStrLn stderr ("  - " <> rcPath r)) (optRepos options)
    runConverge options
@@ -0,0 +1,124 @@
+Changes
+=======
+
+Version 0.4.4.0
+----------
+* Use hinotify and -DHAVE_NATIVE_WATCHER for FreeBSD (#121)
+* Start testing FreeBSD in CI (#122)
+
+Version 0.4.3.0
+----------
+* Use polling as a generic fallback and add support for WASM (https://github.com/haskell-fswatch/hfsnotify/pull/110)
+* Gracefully handle broken symlinks (https://github.com/haskell-fswatch/hfsnotify/pull/120)
+
+Version 0.4.2.0
+----------
+
+* Bump hfsevents constraint to >= 0.1.8 to pick up race condition fix (see https://github.com/luite/hfsevents/pull/19).
+* Compatibility with text-2.1.2 and an upper bound of 2.2.
+* Lots of CI and test improvements.
+
+Version 0.4.1.1
+---------------
+
+* Document polling interval units (#111).
+* Fix compat with text-2.1.2 (closes #116).
+* Remove some redundant cleanup code paths.
+
+Version 0.4.1.0
+---------------
+
+* Add `unliftio` lower bound (#106).
+* Change the tests back to a test-suite to avoid building for library users. (#107).
+* Fix up Windows compatibility.
+* Export `WatchConfig` type (#108).
+
+Version 0.4.0.1
+---------------
+
+* Fix compatibility with *BSD.
+
+Version 0.4.0.0
+---------------
+
+API breaking update.
+
+* New options for threading control (single-threaded, thread-per-watch, and thread-per-manager).
+* Revamp `WatchConfig` options to be less confusing and reduce boolean blindness.
+* Pull out debouncing stuff, since it was never correct as it simply took the last event affecting a given file in the debounce period. Debouncing is currently not included, and should be handled as an orthogonal concern. I'd like to include some debouncing logic, but didn't want to delay this release any longer.
+  * We now expose `type DebounceFn = Action -> IO Action`, which represents an arbitrary debouncer. All debouncers should be in the form of one of these functions.
+  * A robust state machine debouncer is in progress but not fully implemented yet; see the `state-machine` branch.
+  * Contributions are welcome! We can potentially add multiple debouncers of different complexity as modules under `System.FSNotify.Debounce.*`.
+* Don't silently fall back to polling on failure of native watcher.
+  Instead, throw an exception which the user can recover from by switching to polling.
+* Add ModifiedAttributes event type + Linux support.
+* Add confOnHandlerException to be able to control what happens when a handler throws an exception.
+* WatchConfig constructor is no longer exposed. Instead use `defaultConfig {...}` with the accessors.
+
+Version 0.3.0.0
+---------------
+
+API breaking update with a number of bugfixes and improvements.
+
+* Now we can detect directory creation/deletion. A boolean flag has been added
+  to `Event` to indicate if the event pertains to a directory or not. This is the
+  only API change.
+* Test stability improvements + CI test suites now passing on Windows, Linux, and Mac.
+* Interpreting OSX hfsevents flags is more sane now (see comments in OSX.hs for details).
+* Improve a race condition when adding watches on Linux.
+* Improve robustness of the PollManager.
+* Fix double call to `closeHandle` on Windows.
+* Remove comments about locking from the documentation.
+
+Version 0.2.1.2
+---------------
+
+Update to the new hinotify API (v0.3.10)
+
+Version 0.2.1.1
+---------------
+
+Catch IO exceptions when initialising inotify on Linux
+
+Version 0.2.1
+-------------
+
+Don't use `system-filepath`
+
+Version 0.2
+-----------
+
+Use filepath instead of deprecated system-filepath
+
+Version 0.1.0.3
+---------------
+
+* Fix the tests
+
+Version 0.1.0.2
+---------------
+
+* Restore compatibility with GHC 7.4
+* Fix a bug in `treeExtAny`, which previously work identically to
+  `treeExtExists`
+* Improve documentation
+
+Version 0.1.0.1
+---------------
+
+Include CHANGELOG.md and README.md in the source distribution.
+
+Version 0.1
+-----------
+
+* Allow to stop a listening job. Note this changes the return type of watching
+  functions from `()` to `IO ()`.
+* Previously, some care was taken to prevent multiple callbacks from running
+  simultaneously. It is now the user's responsibility. See
+  [#43](https://github.com/haskell-fswatch/hfsnotify/issues/43) for details.
+* Previously, paths returned to callbacks were relative on Windows. Now they are
+  absolute, like on the other platforms.
+* The `WatchConfig` type has changed. Previously, it only specified debouncing
+  parameters. Now it also contains polling parameters.
+* The `isPollingManager` function is added to determine, at runtime, whether the
+  polling implementation is used.
@@ -0,0 +1,30 @@
+Copyright (c) 2012, Mark Dittmer
+
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+
+    * Neither the name of Mark Dittmer nor the names of other
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
@@ -0,0 +1,18 @@
+![CI](https://github.com/haskell-fswatch/hfsnotify/workflows/CI/badge.svg)
+=========
+
+Unified Haskell interface for basic file system notifications.
+
+This is a library. There are executables built on top of it.
+
+* [spy](https://hackage.haskell.org/package/spy)
+* [steeloverseer](https://github.com/schell/steeloverseer)
+
+
+Requirements
+============
+
+Windows
+-------
+
+compile with -fthreaded
@@ -0,0 +1,11 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+
+
+
+--
+
+import Distribution.Simple
+
+main = defaultMain
@@ -0,0 +1,35 @@
+{-# LANGUAGE NumericUnderscores #-}
+{-# LANGUAGE QuasiQuotes #-}
+
+module Main where
+
+import Control.Concurrent
+import Data.String.Interpolate
+import System.FSNotify
+import System.FilePath
+import UnliftIO.Temporary
+
+
+main :: IO ()
+main = do
+  withSystemTempDirectory "fsnotify-foo" $ \dir -> do
+    putStrLn [i|Starting watch on dir: #{dir}|]
+
+    let conf = defaultConfig
+
+    withManagerConf conf $ \mgr -> do
+      stop <- watchDir mgr dir (const True) $ \ev -> do
+        putStrLn [i|Got event: #{ev}|]
+      threadDelay 3_000_000
+
+      putStrLn [i|Writing to #{dir </> "bar"}|]
+      writeFile (dir </> "bar") "asdf"
+      threadDelay 3_000_000
+
+      putStrLn [i|Stopping|]
+      stop
+      putStrLn [i|Stopped|]
+      threadDelay 3_000_000
+
+    putStrLn [i|Exited withManagerConf|]
+    threadDelay 3_000_000
@@ -0,0 +1,148 @@
+cabal-version: 1.12
+
+-- This file has been generated from package.yaml by hpack version 0.38.0.
+--
+-- see: https://github.com/sol/hpack
+
+name:           fsnotify
+version:        0.4.4.0
+synopsis:       Cross platform library for file change notification.
+description:    Cross platform library for file creation, modification, and deletion notification. This library builds upon existing libraries for platform-specific Windows, Mac, and Linux filesystem event notification.
+category:       Filesystem
+homepage:       https://github.com/haskell-fswatch/hfsnotify
+author:         Mark Dittmer <mark.s.dittmer@gmail.com>, Niklas Broberg
+maintainer:     Tom McLaughlin <tom@codedown.io>
+license:        BSD3
+license-file:   LICENSE
+build-type:     Simple
+extra-source-files:
+    README.md
+    CHANGELOG.md
+    test/Main.hs
+
+library
+  exposed-modules:
+      System.FSNotify
+      System.FSNotify.Devel
+  other-modules:
+      System.FSNotify.Find
+      System.FSNotify.Listener
+      System.FSNotify.Path
+      System.FSNotify.Polling
+      System.FSNotify.Types
+  hs-source-dirs:
+      src
+  default-extensions:
+      ScopedTypeVariables
+  ghc-options: -Wall
+  build-depends:
+      async >=2.0.0.0
+    , base >=4.8 && <5
+    , bytestring >=0.10.2
+    , containers >=0.4
+    , directory >=1.3.0.0
+    , filepath >=1.3.0.0
+    , monad-control >=1.0.0.0
+    , safe-exceptions >=0.1.0.0
+    , text >=0.11.0 && <2.2
+    , time >=1.1
+    , unix-compat >=0.2
+  default-language: Haskell2010
+  if os(linux) || os(windows) || os(darwin) || os(freebsd)
+    cpp-options: -DHAVE_NATIVE_WATCHER
+  if os(linux) || os(freebsd)
+    other-modules:
+        System.FSNotify.Linux
+        System.FSNotify.Linux.Util
+    build-depends:
+        unix >=2.7.1.0
+  if os(linux) && impl(ghc >= 9.10)
+    build-depends:
+        hinotify >=0.4.2
+  if os(linux) && impl(ghc < 9.10)
+    build-depends:
+        hinotify >=0.3.9
+  if os(windows)
+    other-modules:
+        System.FSNotify.Win32
+        System.Win32.FileNotify
+        System.Win32.Notify
+    hs-source-dirs:
+        win-src
+    build-depends:
+        Win32
+  if os(darwin)
+    other-modules:
+        System.FSNotify.OSX
+    build-depends:
+        hfsevents >=0.1.8
+  if os(freebsd)
+    build-depends:
+        hinotify >=0.4.1
+
+executable example
+  main-is: Main.hs
+  other-modules:
+      Paths_fsnotify
+  hs-source-dirs:
+      example
+  default-extensions:
+      ScopedTypeVariables
+  ghc-options: -Wall
+  build-depends:
+      base
+    , directory
+    , exceptions
+    , filepath
+    , fsnotify
+    , monad-logger
+    , random
+    , retry
+    , safe-exceptions
+    , string-interpolate
+    , temporary
+    , unix-compat
+    , unliftio
+  default-language: Haskell2010
+  if os(linux) || os(windows) || os(darwin) || os(freebsd)
+    cpp-options: -DHAVE_NATIVE_WATCHER
+  if !arch(wasm32)
+    ghc-options: -threaded
+
+test-suite tests
+  type: exitcode-stdio-1.0
+  main-is: Main.hs
+  other-modules:
+      FSNotify.Test.EventTests
+      FSNotify.Test.Util
+      Paths_fsnotify
+  hs-source-dirs:
+      test
+  default-extensions:
+      ScopedTypeVariables
+  ghc-options: -threaded -Wall
+  build-depends:
+      async >=2
+    , base >=4.3.1.0
+    , directory
+    , exceptions
+    , filepath
+    , fsnotify
+    , monad-logger
+    , random
+    , retry
+    , safe-exceptions
+    , string-interpolate
+    , temporary
+    , unix-compat
+    , unliftio >=0.2.20
+  default-language: Haskell2010
+  if os(linux) || os(windows) || os(darwin) || os(freebsd)
+    cpp-options: -DHAVE_NATIVE_WATCHER
+  if os(windows)
+    build-depends:
+        Win32
+      , sandwich >=0.1.1.1
+  else
+    build-depends:
+        sandwich
@@ -0,0 +1,226 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ExistentialQuantification #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RecordWildCards #-}
+
+-- | This library does not currently report changes made to directories,
+-- only files within watched directories.
+--
+-- Minimal example:
+--
+-- >{-# LANGUAGE OverloadedStrings #-} -- for FilePath literals
+-- >
+-- >import System.FSNotify
+-- >import Control.Concurrent (threadDelay)
+-- >import Control.Monad (forever)
+-- >
+-- >main =
+-- >  withManager $ \mgr -> do
+-- >    -- start a watching job (in the background)
+-- >    watchDir
+-- >      mgr          -- manager
+-- >      "."          -- directory to watch
+-- >      (const True) -- predicate
+-- >      print        -- action
+-- >
+-- >    -- sleep forever (until interrupted)
+-- >    forever $ threadDelay 1000000
+
+module System.FSNotify (
+  -- * Events
+    Event(..)
+  , EventIsDirectory(..)
+  , EventChannel
+  , Action
+  , ActionPredicate
+
+  -- * Starting/Stopping
+  , WatchManager
+  , withManager
+  , startManager
+  , stopManager
+
+  -- * Configuration
+  , defaultConfig
+  , WatchConfig
+  , confWatchMode
+  , confThreadingMode
+  , confOnHandlerException
+  , WatchMode(..)
+  , ThreadingMode(..)
+
+  -- * Lower level
+  , withManagerConf
+  , startManagerConf
+  , StopListening
+
+  -- * Watching
+  , watchDir
+  , watchDirChan
+  , watchTree
+  , watchTreeChan
+  ) where
+
+import Prelude hiding (FilePath)
+
+import Control.Concurrent
+import Control.Concurrent.Async
+import Control.Exception.Safe as E
+import Control.Monad
+import Control.Monad.IO.Class
+import qualified Data.Text as T
+import System.FSNotify.Polling
+import System.FSNotify.Types
+import System.FilePath
+
+import System.FSNotify.Listener (ListenFn, StopListening)
+
+#if !MIN_VERSION_base(4,11,0)
+import Data.Monoid
+#endif
+
+#if defined(linux_HOST_OS) || defined(freebsd_HOST_OS)
+import System.FSNotify.Linux
+#endif
+
+#ifdef mingw32_HOST_OS
+import System.FSNotify.Win32
+#endif
+
+#ifdef darwin_HOST_OS
+import System.FSNotify.OSX
+#endif
+
+
+-- | Watch manager. You need one in order to create watching jobs.
+data WatchManager = forall manager argType. FileListener manager argType =>
+  WatchManager {
+    watchManagerConfig :: WatchConfig
+    , watchManagerManager :: manager
+    , watchManagerGlobalChan :: Maybe (EventAndActionChannel, Async ())
+    }
+
+-- | Default configuration
+--
+-- * Uses OS watch mode (if possible) and single thread.
+defaultConfig :: WatchConfig
+defaultConfig = WatchConfig {
+#ifndef HAVE_NATIVE_WATCHER
+  confWatchMode = WatchModePoll 500000
+#else
+  confWatchMode = WatchModeOS
+#endif
+  , confThreadingMode = SingleThread
+  , confOnHandlerException = defaultOnHandlerException
+  }
+
+defaultOnHandlerException :: SomeException -> IO ()
+defaultOnHandlerException e = putStrLn ("fsnotify: handler threw exception: " <> show e)
+
+-- | Perform an IO action with a WatchManager in place.
+-- Tear down the WatchManager after the action is complete.
+withManager :: (WatchManager -> IO a) -> IO a
+withManager  = withManagerConf defaultConfig
+
+-- | Start a file watch manager.
+-- Directories can only be watched when they are managed by a started
+-- watch manager.
+-- When finished watching. you must release resources via 'stopManager'.
+-- It is preferrable if possible to use 'withManager' to handle this
+-- automatically.
+startManager :: IO WatchManager
+startManager = startManagerConf defaultConfig
+
+-- | Stop a file watch manager.
+-- Stopping a watch manager will immediately stop
+-- watching for files and free resources.
+stopManager :: WatchManager -> IO ()
+stopManager (WatchManager {..}) = do
+  liftIO $ killSession watchManagerManager
+  case watchManagerGlobalChan of
+    Nothing -> return ()
+    Just (_, t) -> cancel t
+
+-- | Like 'withManager', but configurable.
+withManagerConf :: WatchConfig -> (WatchManager -> IO a) -> IO a
+withManagerConf conf = bracket (startManagerConf conf) stopManager
+
+-- | Like 'startManager', but configurable.
+startManagerConf :: WatchConfig -> IO WatchManager
+startManagerConf conf = do
+# ifdef mingw32_HOST_OS
+  -- See https://github.com/haskell-fswatch/hfsnotify/issues/50
+  unless rtsSupportsBoundThreads $ throwIO $ userError "startManagerConf must be called with -threaded on Windows"
+# endif
+
+  case confWatchMode conf of
+    WatchModePoll interval -> WatchManager conf <$> liftIO (createPollManager interval) <*> globalWatchChan
+#ifdef HAVE_NATIVE_WATCHER
+    WatchModeOS -> liftIO (initSession ()) >>= createManager
+#endif
+
+  where
+#ifdef HAVE_NATIVE_WATCHER
+    createManager :: Either T.Text NativeManager -> IO WatchManager
+    createManager (Right nativeManager) = WatchManager conf nativeManager <$> globalWatchChan
+    createManager (Left err) = throwIO $ userError $ T.unpack $ "Error: couldn't start native file manager: " <> err
+#endif
+
+    globalWatchChan = case confThreadingMode conf of
+      SingleThread -> do
+        globalChan <- newChan
+        globalReaderThread <- async $ forever $ do
+          (event, action) <- readChan globalChan
+          tryAny (action event) >>= \case
+            Left _ -> return () -- TODO: surface the exception somehow?
+            Right () -> return ()
+        return $ Just (globalChan, globalReaderThread)
+      _ -> return Nothing
+
+-- | Watch the immediate contents of a directory by streaming events to a Chan.
+-- Watching the immediate contents of a directory will only report events
+-- associated with files within the specified directory, and not files
+-- within its subdirectories.
+watchDirChan :: WatchManager -> FilePath -> ActionPredicate -> EventChannel -> IO StopListening
+watchDirChan (WatchManager {..}) path actionPredicate chan = listen watchManagerConfig watchManagerManager path actionPredicate (writeChan chan)
+
+-- | Watch all the contents of a directory by streaming events to a Chan.
+-- Watching all the contents of a directory will report events associated with
+-- files within the specified directory and its subdirectories.
+watchTreeChan :: WatchManager -> FilePath -> ActionPredicate -> EventChannel -> IO StopListening
+watchTreeChan (WatchManager {..}) path actionPredicate chan = listenRecursive watchManagerConfig watchManagerManager path actionPredicate (writeChan chan)
+
+-- | Watch the immediate contents of a directory by committing an Action for each event.
+-- Watching the immediate contents of a directory will only report events
+-- associated with files within the specified directory, and not files
+-- within its subdirectories.
+watchDir :: WatchManager -> FilePath -> ActionPredicate -> Action -> IO StopListening
+watchDir wm@(WatchManager {watchManagerConfig}) fp actionPredicate action = threadChan listen wm fp actionPredicate wrappedAction
+  where wrappedAction x = handle (confOnHandlerException watchManagerConfig) (action x)
+
+-- | Watch all the contents of a directory by committing an Action for each event.
+-- Watching all the contents of a directory will report events associated with
+-- files within the specified directory and its subdirectories.
+watchTree :: WatchManager -> FilePath -> ActionPredicate -> Action -> IO StopListening
+watchTree wm@(WatchManager {watchManagerConfig}) fp actionPredicate action = threadChan listenRecursive wm fp actionPredicate wrappedAction
+  where wrappedAction x = handle (confOnHandlerException watchManagerConfig) (action x)
+
+-- * Main threading logic
+
+threadChan :: (forall a b. ListenFn a b) -> WatchManager -> FilePath -> ActionPredicate -> Action -> IO StopListening
+threadChan listenFn (WatchManager {watchManagerGlobalChan=(Just (globalChan, _)), ..}) path actPred action =
+  listenFn watchManagerConfig watchManagerManager path actPred (\event -> writeChan globalChan (event, action))
+threadChan listenFn (WatchManager {watchManagerGlobalChan=Nothing, ..}) path actPred action = do
+  let wrappedAction = case confThreadingMode watchManagerConfig of
+        SingleThread -> error "Should never happen"
+        ThreadPerWatch -> action
+        ThreadPerEvent -> void . async . action
+  listenFn watchManagerConfig watchManagerManager path actPred wrappedAction
@@ -0,0 +1,73 @@
+{-# LANGUAGE FlexibleContexts #-}
+
+-- | Some additional functions on top of "System.FSNotify".
+--
+-- Example of compiling scss files with compass
+--
+-- @
+-- compass :: WatchManager -> FilePath -> m ()
+-- compass man dir = do
+--  putStrLn $ "compass " ++ encodeString dir
+--  treeExtExists man dir "scss" $ \fp ->
+--    when ("deploy" `notElem` splitDirectories fp) $ do
+--     let d = encodeString $ head (splitDirectories rel)
+--     system "cd " ++ d ++ "&& bundle exec compass compile"
+--  return ()
+-- @
+
+{-# LANGUAGE NamedFieldPuns #-}
+
+module System.FSNotify.Devel (
+  treeExtAny
+  , treeExtExists
+  , doAllEvents
+  , allEvents
+  , existsEvents
+  ) where
+
+import Data.Text
+import Prelude hiding (FilePath)
+import System.FSNotify
+import System.FSNotify.Path (hasThisExtension)
+import System.FilePath
+
+-- | In the given directory tree, watch for any 'Added' and 'Modified'
+-- events (but ignore 'Removed' events) for files with the given file
+-- extension
+treeExtExists :: WatchManager
+              -> FilePath -- ^ Directory to watch
+              -> Text -- ^ extension
+              -> (FilePath -> IO ()) -- ^ action to run on file
+              -> IO StopListening
+treeExtExists man dir ext action =
+  watchTree man dir (existsEvents $ flip hasThisExtension ext) (doAllEvents action)
+
+-- | In the given directory tree, watch for any events for files with the
+-- given file extension
+treeExtAny :: WatchManager
+           -> FilePath -- ^ Directory to watch
+           -> Text -- ^ extension
+           -> (FilePath -> IO ()) -- ^ action to run on file
+           -> IO StopListening
+treeExtAny man dir ext action =
+  watchTree man dir (allEvents $ flip hasThisExtension ext) (doAllEvents action)
+
+-- | Turn a 'FilePath' callback into an 'Event' callback that ignores the
+-- 'Event' type and timestamp
+doAllEvents :: Monad m => (FilePath -> m ()) -> Event -> m ()
+doAllEvents action = action . eventPath
+
+-- | Turn a 'FilePath' predicate into an 'Event' predicate that accepts
+-- only 'Added', 'Modified', and 'ModifiedAttributes' event types
+existsEvents :: (FilePath -> Bool) -> (Event -> Bool)
+existsEvents filt event =
+  case event of
+    Added {eventPath} -> filt eventPath
+    Modified {eventPath} -> filt eventPath
+    ModifiedAttributes {eventPath} -> filt eventPath
+    _ -> False
+
+-- | Turn a 'FilePath' predicate into an 'Event' predicate that accepts
+-- any event types
+allEvents :: (FilePath -> Bool) -> (Event -> Bool)
+allEvents filt = filt . eventPath
@@ -0,0 +1,32 @@
+-- | Adapted from how Shelly does finding in Shelly.Find
+-- (shelly is BSD-licensed)
+
+module System.FSNotify.Find where
+
+import Control.Monad
+import Control.Monad.IO.Class
+import System.Directory (doesDirectoryExist, listDirectory, pathIsSymbolicLink)
+import System.FilePath
+
+find :: Bool -> FilePath -> IO [FilePath]
+find followSymlinks = find' followSymlinks  []
+
+find' :: Bool -> [FilePath] -> FilePath -> IO [FilePath]
+find' followSymlinks startValue dir = do
+  (rPaths, aPaths) <- lsRelAbs dir
+  foldM visit startValue (zip rPaths aPaths)
+  where
+    visit acc (relativePath, absolutePath) = do
+      isDir <- liftIO $ doesDirectoryExist absolutePath
+      sym <- liftIO $ pathIsSymbolicLink absolutePath
+      let newAcc = relativePath : acc
+      if isDir && (followSymlinks || not sym)
+        then find' followSymlinks newAcc relativePath
+        else return newAcc
+
+lsRelAbs :: FilePath -> IO ([FilePath], [FilePath])
+lsRelAbs fp = do
+  files <- liftIO $ listDirectory fp
+  let absolute = map (fp </>) files
+  let relativized = map (\p -> joinPath [fp, p]) files
+  return (relativized, absolute)
@@ -0,0 +1,180 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE ViewPatterns #-}
+
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module System.FSNotify.Linux (
+  FileListener(..)
+  , NativeManager
+  ) where
+
+import Control.Concurrent.MVar
+import Control.Exception.Safe as E
+import Control.Monad
+import Data.Function
+import Data.Monoid
+import Data.String
+import Data.Time.Clock (UTCTime)
+import Data.Time.Clock.POSIX
+import Prelude hiding (FilePath)
+import System.FSNotify.Find
+import System.FSNotify.Linux.Util
+import System.FSNotify.Listener
+import System.FSNotify.Types
+import System.FilePath ((</>))
+import qualified System.INotify as INo
+import System.Posix.ByteString (RawFilePath)
+import System.Posix.Files (getFileStatus, isDirectory, modificationTimeHiRes)
+
+
+data INotifyListener = INotifyListener { listenerINotify :: INo.INotify }
+
+type NativeManager = INotifyListener
+
+data EventVarietyMismatchException = EventVarietyMismatchException deriving (Show, Typeable)
+instance Exception EventVarietyMismatchException
+
+
+fsnEvents :: RawFilePath -> UTCTime -> INo.Event -> IO [Event]
+fsnEvents basePath' timestamp (INo.Attributes (boolToIsDirectory -> isDir) (Just raw)) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [ModifiedAttributes (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.Modified (boolToIsDirectory -> isDir) (Just raw)) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [Modified (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.Closed (boolToIsDirectory -> isDir) (Just raw) True) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [CloseWrite (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.Created (boolToIsDirectory -> isDir) raw) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [Added (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.MovedOut (boolToIsDirectory -> isDir) raw _cookie) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [Removed (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.MovedIn (boolToIsDirectory -> isDir) raw _cookie) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [Added (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp (INo.Deleted (boolToIsDirectory -> isDir) raw) = do
+  basePath <- fromRawFilePath basePath'
+  fromHinotifyPath raw >>= \name -> return [Removed (basePath </> name) timestamp isDir]
+fsnEvents basePath' timestamp INo.DeletedSelf = do
+  basePath <- fromRawFilePath basePath'
+  return [WatchedDirectoryRemoved basePath timestamp IsDirectory]
+fsnEvents _ _ INo.Ignored = return []
+fsnEvents basePath' timestamp inoEvent = do
+  basePath <- fromRawFilePath basePath'
+  return [Unknown basePath timestamp IsFile (show inoEvent)]
+
+handleInoEvent :: ActionPredicate -> EventCallback -> RawFilePath -> MVar Bool -> INo.Event -> IO ()
+handleInoEvent actPred callback basePath watchStillExistsVar inoEvent = do
+  when (INo.DeletedSelf == inoEvent) $ modifyMVar_ watchStillExistsVar $ const $ return False
+
+  currentTime <- getCurrentTime
+  events <- fsnEvents basePath currentTime inoEvent
+  forM_ events $ \event -> when (actPred event) $ callback event
+
+varieties :: [INo.EventVariety]
+varieties = [INo.Create, INo.Delete, INo.MoveIn, INo.MoveOut, INo.Attrib, INo.Modify, INo.CloseWrite, INo.DeleteSelf]
+
+instance FileListener INotifyListener () where
+  initSession _ = E.handle (\(e :: IOException) -> return $ Left $ fromString $ show e) $ do
+    inotify <- INo.initINotify
+    return $ Right $ INotifyListener inotify
+
+  killSession (INotifyListener {listenerINotify}) = INo.killINotify listenerINotify
+
+  listen _conf (INotifyListener {listenerINotify}) path actPred callback = do
+    rawPath <- toRawFilePath path
+    canonicalRawPath <- canonicalizeRawDirPath rawPath
+    watchStillExistsVar <- newMVar True
+    hinotifyPath <- rawToHinotifyPath canonicalRawPath
+    wd <- INo.addWatch listenerINotify varieties hinotifyPath (handleInoEvent actPred callback canonicalRawPath watchStillExistsVar)
+    return $
+      modifyMVar_ watchStillExistsVar $ \wse -> do
+        when wse $ INo.removeWatch wd
+        return False
+
+  listenRecursive _conf listener initialPath actPred callback = do
+    -- wdVar stores the list of created watch descriptors. We use it to
+    -- cancel the whole recursive listening task.
+    --
+    -- To avoid a race condition (when a new watch is added right after
+    -- we've stopped listening), we replace the MVar contents with Nothing
+    -- to signify that the listening task is cancelled, and no new watches
+    -- should be added.
+    wdVar <- newMVar (Just [])
+
+    let
+      removeWatches wds = forM_ wds $ \(wd, watchStillExistsVar) ->
+        modifyMVar_ watchStillExistsVar $ \wse -> do
+          when wse $
+            handle (\(e :: SomeException) -> putStrLn ("Error removing watch: " <> show wd <> " (" <> show e <> ")"))
+                   (INo.removeWatch wd)
+          return False
+
+      stopListening = modifyMVar_ wdVar $ \x -> maybe (return ()) removeWatches x >> return Nothing
+
+    -- Add watches to this directory plus every sub-directory
+    rawInitialPath <- toRawFilePath initialPath
+    rawCanonicalInitialPath <- canonicalizeRawDirPath rawInitialPath
+    watchDirectoryRecursively listener wdVar actPred callback True rawCanonicalInitialPath
+    traverseAllDirs rawCanonicalInitialPath $ \subPath ->
+      watchDirectoryRecursively listener wdVar actPred callback False subPath
+
+    return stopListening
+
+
+type RecursiveWatches = MVar (Maybe [(INo.WatchDescriptor, MVar Bool)])
+
+watchDirectoryRecursively :: INotifyListener -> RecursiveWatches -> ActionPredicate -> EventCallback -> Bool -> RawFilePath -> IO ()
+watchDirectoryRecursively listener@(INotifyListener {listenerINotify}) wdVar actPred callback isRootWatchedDir rawFilePath = do
+  modifyMVar_ wdVar $ \case
+    Nothing -> return Nothing
+    Just wds -> do
+      watchStillExistsVar <- newMVar True
+      hinotifyPath <- rawToHinotifyPath rawFilePath
+      wd <- INo.addWatch listenerINotify varieties hinotifyPath (handleRecursiveEvent rawFilePath actPred callback watchStillExistsVar isRootWatchedDir listener wdVar)
+      return $ Just ((wd, watchStillExistsVar):wds)
+
+handleRecursiveEvent :: RawFilePath -> ActionPredicate -> EventCallback -> MVar Bool -> Bool -> INotifyListener -> RecursiveWatches -> INo.Event -> IO ()
+handleRecursiveEvent baseDir actPred callback watchStillExistsVar isRootWatchedDir listener wdVar event = do
+  case event of
+    (INo.Created True hiNotifyPath) -> do
+      -- A new directory was created, so add recursive inotify watches to it
+      rawDirPath <- rawFromHinotifyPath hiNotifyPath
+      let newRawDir = baseDir <//> rawDirPath
+      timestampBeforeAddingWatch <- getPOSIXTime
+      watchDirectoryRecursively listener wdVar actPred callback False newRawDir
+
+      newDir <- fromRawFilePath newRawDir
+
+      -- Find all files/folders that might have been created *after* the timestamp, and hence might have been
+      -- missed by the watch
+      -- TODO: there's a chance of this generating double events, fix
+      files <- find False newDir -- TODO: expose the ability to set followSymlinks to True?
+      forM_ files $ \newPath -> do
+        fileStatus <- getFileStatus newPath
+        let modTime = modificationTimeHiRes fileStatus
+        when (modTime > timestampBeforeAddingWatch) $ do
+          let isDir = if isDirectory fileStatus then IsDirectory else IsFile
+          let addedEvent = (Added (newDir </> newPath) (posixSecondsToUTCTime timestampBeforeAddingWatch) isDir)
+          when (actPred addedEvent) $ callback addedEvent
+
+    _ -> return ()
+
+  -- If the watched directory was removed, mark the watch as already removed
+  case event of
+    INo.DeletedSelf -> modifyMVar_ watchStillExistsVar $ const $ return False
+    _ -> return ()
+
+  -- Forward the event. Ignore a DeletedSelf if we're not on the root directory,
+  -- since the watch above us will pick up the delete of that directory.
+  case event of
+    INo.DeletedSelf | not isRootWatchedDir -> return ()
+    _ -> handleInoEvent actPred callback baseDir watchStillExistsVar event
@@ -0,0 +1,100 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE ViewPatterns #-}
+
+module System.FSNotify.Linux.Util (
+  canonicalizePath
+  , canonicalizeRawDirPath
+  , (<//>)
+  , traverseAllDirs
+
+  , boolToIsDirectory
+
+  , fromRawFilePath
+  , toRawFilePath
+
+  , fromHinotifyPath
+
+  , rawToHinotifyPath
+  , rawFromHinotifyPath
+  ) where
+
+import Control.Exception.Safe as E
+import Control.Monad
+import qualified Data.ByteString as BS
+import Data.Function
+import Data.Monoid
+import qualified GHC.Foreign as F
+import GHC.IO.Encoding (getFileSystemEncoding)
+import Prelude hiding (FilePath)
+import System.Directory (canonicalizePath)
+import System.FSNotify.Types
+import System.FilePath (FilePath)
+import System.Posix.ByteString (RawFilePath)
+import System.Posix.Directory.ByteString (openDirStream, readDirStream, closeDirStream)
+import System.Posix.Files (getSymbolicLinkStatus, isDirectory)
+
+
+canonicalizeRawDirPath :: RawFilePath -> IO RawFilePath
+canonicalizeRawDirPath p = fromRawFilePath p >>= canonicalizePath >>= toRawFilePath
+
+-- | Same as </> but for RawFilePath
+-- TODO: make sure this is correct or find in a library
+(<//>) :: RawFilePath -> RawFilePath -> RawFilePath
+x <//> y = x <> "/" <> y
+
+traverseAllDirs :: RawFilePath -> (RawFilePath -> IO ()) -> IO ()
+traverseAllDirs dir cb = traverseAll dir $ \subPath ->
+  -- TODO: wish we didn't need fromRawFilePath here
+  -- TODO: should this follow symlinks? (What then about symlinks that escape the parent?)
+  fromRawFilePath subPath >>= getSymbolicLinkStatus >>= \case
+    (isDirectory -> True) -> cb subPath >> return True
+    _ -> return False
+
+traverseAll :: RawFilePath -> (RawFilePath -> IO Bool) -> IO ()
+traverseAll dir cb = bracket (openDirStream dir) closeDirStream $ \dirStream ->
+  fix $ \loop -> do
+    readDirStream dirStream >>= \case
+      x | BS.null x -> return ()
+      "." -> loop
+      ".." -> loop
+      subDir -> flip finally loop $ do
+        -- TODO: canonicalize?
+        let fullSubDir = dir <//> subDir
+        shouldRecurse <- cb fullSubDir
+        when shouldRecurse $ traverseAll fullSubDir cb
+
+boolToIsDirectory :: Bool -> EventIsDirectory
+boolToIsDirectory False = IsFile
+boolToIsDirectory True = IsDirectory
+
+toRawFilePath :: FilePath -> IO BS.ByteString
+toRawFilePath fp = do
+  enc <- getFileSystemEncoding
+  F.withCString enc fp BS.packCString
+
+fromRawFilePath :: BS.ByteString -> IO FilePath
+fromRawFilePath bs = do
+  enc <- getFileSystemEncoding
+  BS.useAsCString bs (F.peekCString enc)
+
+#if MIN_VERSION_hinotify(0, 3, 10)
+fromHinotifyPath :: BS.ByteString -> IO FilePath
+fromHinotifyPath = fromRawFilePath
+
+rawToHinotifyPath :: BS.ByteString -> IO BS.ByteString
+rawToHinotifyPath = return
+
+rawFromHinotifyPath :: BS.ByteString -> IO BS.ByteString
+rawFromHinotifyPath = return
+#else
+fromHinotifyPath :: FilePath -> IO FilePath
+fromHinotifyPath = return
+
+rawToHinotifyPath :: BS.ByteString -> IO FilePath
+rawToHinotifyPath = fromRawFilePath
+
+rawFromHinotifyPath :: FilePath -> IO BS.ByteString
+rawFromHinotifyPath = toRawFilePath
+#endif
@@ -0,0 +1,48 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE FunctionalDependencies #-}
+{-# LANGUAGE Rank2Types #-}
+{-# LANGUAGE AllowAmbiguousTypes #-}
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+
+module System.FSNotify.Listener (
+  FileListener(..)
+  , StopListening
+  , ListenFn
+  ) where
+
+import Data.Text
+import Prelude hiding (FilePath)
+import System.FSNotify.Types
+import System.FilePath
+
+-- | An action that cancels a watching/listening job.
+type StopListening = IO ()
+
+type ListenFn sessionType argType = FileListener sessionType argType => WatchConfig -> sessionType -> FilePath -> ActionPredicate -> EventCallback -> IO StopListening
+
+-- | A typeclass that imposes structure on watch managers capable of listening
+-- for events, or simulated listening for events.
+class FileListener sessionType argType | sessionType -> argType where
+  -- | Initialize a file listener instance.
+  initSession :: argType -> IO (Either Text sessionType)
+  -- ^ An initialized file listener, or a reason why one wasn't able to start.
+
+  -- | Kill a file listener instance.
+  -- This will immediately stop acting on events for all directories being
+  -- watched.
+  killSession :: sessionType -> IO ()
+
+  -- | Listen for file events associated with the immediate contents of a directory.
+  -- Listening for events associated with immediate contents of a directory will
+  -- only report events associated with files within the specified directory, and
+  -- not files within its subdirectories.
+  listen :: ListenFn sessionType argType
+
+  -- | Listen for file events associated with all the contents of a directory.
+  -- Listening for events associated with all the contents of a directory will
+  -- report events associated with files within the specified directory and its
+  -- subdirectories.
+  listenRecursive :: ListenFn sessionType argType
@@ -0,0 +1,140 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+
+{-# LANGUAGE MultiWayIf #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+
+module System.FSNotify.OSX (
+  FileListener(..)
+  , NativeManager
+  ) where
+
+import Control.Concurrent
+import Control.Monad
+import Data.Bits
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Time.Clock (UTCTime, getCurrentTime)
+import Data.Unique
+import Data.Word
+import Prelude hiding (FilePath)
+import System.Directory
+import System.FSNotify.Listener
+import System.FSNotify.Path (canonicalizeDirPath)
+import System.FSNotify.Types
+import System.FilePath
+import qualified System.OSX.FSEvents as FSE
+
+
+data WatchData = WatchData FSE.EventStream EventCallback
+
+type WatchMap = Map Unique WatchData
+data OSXManager = OSXManager (MVar WatchMap)
+type NativeManager = OSXManager
+
+nil :: Word64
+nil = 0x00
+
+-- OS X reports the absolute (canonical) path without a trailing slash. Add
+-- the trailing slash when the path refers to a directory
+canonicalEventPath :: FSE.Event -> FilePath
+canonicalEventPath event =
+  if flags .&. dirFlag /= nil then addTrailingPathSeparator path else path
+  where
+    flags = FSE.eventFlags event
+    dirFlag = FSE.eventFlagItemIsDir
+    path = FSE.eventPath event
+
+-- We have to be careful about interpreting the flags in a given event, because
+-- "really it's an OR of all the changes made since the FSEventsListener is created"
+-- See https://stackoverflow.com/questions/18415285/osx-fseventstreameventflags-not-working-correctly
+-- Thus, we try to look at whether the path exists or not to determine whether it was created, modified, etc.
+
+-- Note that there's still some bugs possible due to event coalescing, which the docs say is a possibility:
+-- for example, a file could be created and modified within a short time interval, and then we'd only emit one
+-- event (the "modified" one, given the logic below)
+-- See https://developer.apple.com/library/content/documentation/Darwin/Conceptual/FSEvents_ProgGuide/UsingtheFSEventsFramework/UsingtheFSEventsFramework.html
+fsnEvents :: UTCTime -> FSE.Event -> IO [Event]
+fsnEvents timestamp e = do
+  -- Note: we *don't* want to use the canonical event path in the existence check, because of the aforementioned crazy event coalescing.
+  -- For example, suppose a directory is created and deleted, and then a file is created with the same name. This means the isDirectory flag might
+  -- still be turned on, which could lead us to construct a canonical event path with a trailing slash, which would then cause the existence
+  -- check to fail and make us think the file was removed.
+  -- The upshot of this is that the canonical event paths in the events we emit can't really be trusted, but hey, that's what the extra flag
+  -- on the event is for :(
+  exists <- doesPathExist $ FSE.eventPath e
+
+  -- Uncomment for an easy way to see flag activity when testing manually
+  -- putStrLn $ show ["Event", show e, "isDirectory", show isDirectory, "isFile", show isFile, "isModified", show isModified, "isCreated", show isCreated, "path", path e, "exists", show exists]
+
+  return $ if | exists && isModified -> [Modified (path e) timestamp isDirectory]
+              | exists && isModifiedAttributes -> [ModifiedAttributes (path e) timestamp isDirectory]
+              | exists && isCreated -> [Added (path e) timestamp isDirectory]
+              | (not exists) && hasFlag e FSE.eventFlagItemRemoved -> [Removed (path e) timestamp isDirectory]
+
+              -- Rename stuff
+              | exists && isRenamed -> [Added (path e) timestamp isDirectory]
+              | (not exists) && isRenamed -> [Removed (path e) timestamp isDirectory]
+
+              | otherwise -> []
+  where
+    isDirectory = if hasFlag e FSE.eventFlagItemIsDir then IsDirectory else IsFile
+    isFile = hasFlag e FSE.eventFlagItemIsFile
+    isCreated = hasFlag e FSE.eventFlagItemCreated
+    isRenamed = hasFlag e FSE.eventFlagItemRenamed
+    isModified = hasFlag e FSE.eventFlagItemModified
+    isModifiedAttributes = hasFlag e FSE.eventFlagItemInodeMetaMod
+    path = canonicalEventPath
+    hasFlag event flag = FSE.eventFlags event .&. flag /= 0
+
+handleFSEEvent :: Bool -> ActionPredicate -> EventCallback -> FilePath -> FSE.Event -> IO ()
+handleFSEEvent isRecursive actPred callback dirPath fseEvent = do
+  currentTime <- getCurrentTime
+  events <- fsnEvents currentTime fseEvent
+  forM_ events $ \event ->
+    when (actPred event && (isRecursive || (isDirectlyInside dirPath event))) $
+      callback event
+
+-- | For non-recursive monitoring, test if an event takes place directly inside the monitored folder
+isDirectlyInside :: FilePath -> Event -> Bool
+isDirectlyInside dirPath event = isRelevantFileEvent || isRelevantDirEvent
+  where
+    isRelevantFileEvent = (eventIsDirectory event == IsFile) && (takeDirectory dirPath == (takeDirectory $ eventPath event))
+    isRelevantDirEvent = (eventIsDirectory event == IsDirectory) && (takeDirectory dirPath == (takeDirectory $ takeDirectory $ eventPath event))
+
+listenFn :: (
+  ActionPredicate -> EventCallback -> FilePath -> FSE.Event -> IO a
+  )
+  -> WatchConfig
+  -> OSXManager
+  -> FilePath
+  -> ActionPredicate
+  -> EventCallback
+  -> IO StopListening
+listenFn handler conf (OSXManager mvarMap) path actPred callback = do
+  path' <- canonicalizeDirPath path
+  unique <- newUnique
+  eventStream <- FSE.eventStreamCreate [path'] 0.0 True False True (handler actPred callback path')
+  modifyMVar_ mvarMap $ \watchMap -> return (Map.insert unique (WatchData eventStream callback) watchMap)
+  return $ do
+    FSE.eventStreamDestroy eventStream
+    modifyMVar_ mvarMap $ \watchMap -> return $ Map.delete unique watchMap
+
+instance FileListener OSXManager () where
+  initSession _ = do
+    (v1, v2, _) <- FSE.osVersion
+    if not $ v1 > 10 || (v1 == 10 && v2 > 6) then return $ Left "Unsupported OS version" else
+      (Right . OSXManager) <$> newMVar Map.empty
+
+  killSession (OSXManager mvarMap) = do
+    watchMap <- readMVar mvarMap
+    forM_ (Map.elems watchMap) eventStreamDestroy'
+    where
+      eventStreamDestroy' :: WatchData -> IO ()
+      eventStreamDestroy' (WatchData eventStream _) = FSE.eventStreamDestroy eventStream
+
+  listen = listenFn $ handleFSEEvent False
+  listenRecursive = listenFn $ handleFSEEvent True
@@ -0,0 +1,83 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE CPP #-}
+
+module System.FSNotify.Path (
+  findFiles
+  , findFilesAndDirs
+  , canonicalizeDirPath
+  , canonicalizePath
+  , hasThisExtension
+  ) where
+
+import Control.Monad
+import qualified Data.Text as T
+import Prelude hiding (FilePath)
+import qualified System.Directory as D
+import System.FilePath
+import System.PosixCompat.Files as PF
+
+getDirectoryContentsPath :: FilePath -> IO [FilePath]
+getDirectoryContentsPath path =
+  ((map (path </>)) . filter (not . dots) <$> D.getDirectoryContents path) >>= filterM exists
+  where
+#if MIN_VERSION_directory(1, 2, 7)
+    exists x = D.doesPathExist x
+#else
+    exists x = (||) <$> D.doesFileExist x <*> D.doesDirectoryExist x
+#endif
+    dots "."  = True
+    dots ".." = True
+    dots _    = False
+
+fileDirContents :: FilePath -> IO ([FilePath], [FilePath])
+fileDirContents path = do
+  contents <- getDirectoryContentsPath path
+  stats <- mapM getFileStatus contents
+  let pairs = zip stats contents
+  let files = [ f | (s, f) <- pairs, PF.isRegularFile s]
+  let dirs = [ d | (s, d) <- pairs, PF.isDirectory s]
+  return (files, dirs)
+
+findAllFiles :: FilePath -> IO [FilePath]
+findAllFiles path = do
+  (files, dirs) <- fileDirContents path
+  nestedFiles <- mapM findAllFiles dirs
+  return (files ++ concat nestedFiles)
+
+findImmediateFiles :: FilePath -> IO [FilePath]
+findImmediateFiles = fileDirContents >=> mapM D.canonicalizePath . fst
+
+-- * Exported functions below this point
+
+findFiles :: Bool -> FilePath -> IO [FilePath]
+findFiles True path  = findAllFiles       =<< canonicalizeDirPath path
+findFiles False path = findImmediateFiles =<<  canonicalizeDirPath path
+
+findFilesAndDirs :: Bool -> FilePath -> IO [FilePath]
+findFilesAndDirs False path = getDirectoryContentsPath =<< canonicalizeDirPath path
+findFilesAndDirs True path = do
+  (files, dirs) <- fileDirContents path
+  nestedFilesAndDirs <- concat <$> mapM (findFilesAndDirs False) dirs
+  return (files ++ dirs ++ nestedFilesAndDirs)
+
+-- | add a trailing slash to ensure the path indicates a directory
+addTrailingSlash :: FilePath -> FilePath
+addTrailingSlash = addTrailingPathSeparator
+
+canonicalizeDirPath :: FilePath -> IO FilePath
+canonicalizeDirPath path = addTrailingSlash `fmap` D.canonicalizePath path
+
+-- | bugfix older version of canonicalizePath (system-fileio <= 0.3.7) loses trailing slash
+canonicalizePath :: FilePath -> IO FilePath
+canonicalizePath path = let was_dir = null (takeFileName path) in
+  if not was_dir then D.canonicalizePath path
+  else canonicalizeDirPath path
+
+hasThisExtension :: FilePath -> T.Text -> Bool
+hasThisExtension p ext = takeExtension p == T.unpack ext
@@ -0,0 +1,147 @@
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TypeSynonymInstances #-}
+{-# LANGUAGE FlexibleInstances #-}
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+
+module System.FSNotify.Polling (
+  createPollManager
+  , PollManager(..)
+  , FileListener(..)
+  ) where
+
+import Control.Concurrent
+import Control.Exception.Safe
+import Control.Monad (forM_)
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Data.Maybe
+import Data.Time.Clock (UTCTime)
+import Data.Time.Clock.POSIX
+import Prelude hiding (FilePath)
+import System.Directory (doesDirectoryExist)
+import System.FSNotify.Listener
+import System.FSNotify.Path (findFilesAndDirs, canonicalizeDirPath)
+import System.FSNotify.Types
+import System.FilePath
+import System.PosixCompat.Files
+import System.PosixCompat.Types
+
+
+data EventType = AddedEvent
+               | ModifiedEvent
+               | RemovedEvent
+
+newtype WatchKey = WatchKey ThreadId deriving (Eq, Ord)
+data WatchData = WatchData FilePath EventCallback
+type WatchMap = Map WatchKey WatchData
+data PollManager = PollManager {
+  pollManagerWatchMap :: MVar WatchMap
+  , pollManagerInterval :: Int
+  }
+
+generateEvent :: UTCTime -> EventIsDirectory -> EventType -> FilePath -> Maybe Event
+generateEvent timestamp isDir AddedEvent filePath = Just (Added filePath timestamp isDir)
+generateEvent timestamp isDir ModifiedEvent filePath = Just (Modified filePath timestamp isDir)
+generateEvent timestamp isDir RemovedEvent filePath = Just (Removed filePath timestamp isDir)
+
+generateEvents :: UTCTime -> EventType -> [(FilePath, EventIsDirectory)] -> [Event]
+generateEvents timestamp eventType = mapMaybe (\(path, isDir) -> generateEvent timestamp isDir eventType path)
+
+-- | Do not return modified events for directories.
+-- These can arise when files are created inside subdirectories, resulting in the modification time
+-- of the directory being bumped. However, to increase consistency with the other FileListeners,
+-- we ignore these events.
+handleEvent :: EventCallback -> ActionPredicate -> Event -> IO ()
+handleEvent _ _ (Modified _ _ IsDirectory) = return ()
+handleEvent callback actPred event
+  | actPred event = callback event
+  | otherwise = return ()
+
+pathModMap :: Bool -> FilePath -> IO (Map FilePath (UTCTime, EventIsDirectory))
+pathModMap recursive path = findFilesAndDirs recursive path >>= pathModMap'
+  where
+    pathModMap' :: [FilePath] -> IO (Map FilePath (UTCTime, EventIsDirectory))
+    pathModMap' files = (Map.fromList . catMaybes) <$> mapM pathAndInfo files
+
+    pathAndInfo :: FilePath -> IO (Maybe (FilePath, (UTCTime, EventIsDirectory)))
+    pathAndInfo p = handle (\(_ :: IOException) -> return Nothing) $ do
+      modTime <- getModificationTime p
+      isDir <- doesDirectoryExist p
+      return $ Just (p, (modTime, if isDir then IsDirectory else IsFile))
+
+pollPath :: Int -> Bool -> EventCallback -> FilePath -> ActionPredicate -> Map FilePath (UTCTime, EventIsDirectory) -> IO ()
+pollPath interval recursive callback filePath actPred oldPathMap = do
+  threadDelay interval
+  maybeNewPathMap <- handle (\(_ :: IOException) -> return Nothing) (Just <$> pathModMap recursive filePath)
+  case maybeNewPathMap of
+    -- Something went wrong while listing directories; we'll try again on the next poll
+    Nothing -> pollPath interval recursive callback filePath actPred oldPathMap
+
+    Just newPathMap -> do
+      currentTime <- getCurrentTime
+      let deletedMap = Map.difference oldPathMap newPathMap
+          createdMap = Map.difference newPathMap oldPathMap
+          modifiedAndCreatedMap = Map.differenceWith modifiedDifference newPathMap oldPathMap
+          modifiedMap = Map.difference modifiedAndCreatedMap createdMap
+          generateEvents' = generateEvents currentTime
+
+      handleEvents $ generateEvents' AddedEvent [(path, isDir) | (path, (_, isDir)) <- Map.toList createdMap]
+      handleEvents $ generateEvents' ModifiedEvent [(path, isDir) | (path, (_, isDir)) <- Map.toList modifiedMap]
+      handleEvents $ generateEvents' RemovedEvent [(path, isDir) | (path, (_, isDir)) <- Map.toList deletedMap]
+
+      pollPath interval recursive callback filePath actPred newPathMap
+
+  where
+    modifiedDifference :: (UTCTime, EventIsDirectory) -> (UTCTime, EventIsDirectory) -> Maybe (UTCTime, EventIsDirectory)
+    modifiedDifference (newTime, isDir1) (oldTime, isDir2)
+      | oldTime /= newTime || isDir1 /= isDir2 = Just (newTime, isDir1)
+      | otherwise = Nothing
+
+    handleEvents :: [Event] -> IO ()
+    handleEvents = mapM_ (handleEvent callback actPred)
+
+
+-- Additional init function exported to allow startManager to unconditionally
+-- create a poll manager as a fallback when other managers will not instantiate.
+createPollManager :: Int -> IO PollManager
+createPollManager interval  = PollManager <$> newMVar Map.empty <*> pure interval
+
+killWatchingThread :: WatchKey -> IO ()
+killWatchingThread (WatchKey threadId) = killThread threadId
+
+killAndUnregister :: MVar WatchMap -> WatchKey -> IO ()
+killAndUnregister mvarMap wk = do
+  _ <- withMVar mvarMap $ \m -> do
+    killWatchingThread wk
+    return $ Map.delete wk m
+  return ()
+
+listen' :: Bool -> WatchConfig -> PollManager -> FilePath -> ActionPredicate -> EventCallback -> IO (IO ())
+listen' isRecursive _conf (PollManager mvarMap interval) path actPred callback = do
+  path' <- canonicalizeDirPath path
+  pmMap <- pathModMap isRecursive path'
+  threadId <- forkIO $ pollPath interval isRecursive callback path' actPred pmMap
+  let wk = WatchKey threadId
+  modifyMVar_ mvarMap $ return . Map.insert wk (WatchData path' callback)
+  return $ killAndUnregister mvarMap wk
+
+
+instance FileListener PollManager Int where
+  initSession interval = Right <$> createPollManager interval
+
+  killSession (PollManager mvarMap _) = do
+    watchMap <- readMVar mvarMap
+    forM_ (Map.keys watchMap) killWatchingThread
+
+  listen = listen' False
+
+  listenRecursive = listen' True
+
+getModificationTime :: FilePath -> IO UTCTime
+getModificationTime p = fromEpoch . modificationTime <$> getFileStatus p
+
+fromEpoch :: EpochTime -> UTCTime
+fromEpoch = posixSecondsToUTCTime . realToFrac
@@ -0,0 +1,102 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+{-# LANGUAGE CPP #-}
+
+module System.FSNotify.Types (
+  act
+  , ActionPredicate
+  , Action
+  , DebounceFn
+  , WatchConfig(..)
+  , WatchMode(..)
+  , ThreadingMode(..)
+  , Event(..)
+  , EventIsDirectory(..)
+  , EventCallback
+  , EventChannel
+  , EventAndActionChannel
+  , IOEvent
+  ) where
+
+import Control.Concurrent.Chan
+import Control.Exception.Safe
+import Data.IORef (IORef)
+import Data.Time.Clock (UTCTime)
+import Prelude hiding (FilePath)
+import System.FilePath
+
+data EventIsDirectory = IsFile | IsDirectory
+  deriving (Show, Eq)
+
+-- | A file event reported by a file watcher. Each event contains the
+-- canonical path for the file and a timestamp guaranteed to be after the
+-- event occurred (timestamps represent current time when FSEvents receives
+-- it from the OS and/or platform-specific Haskell modules).
+data Event =
+    Added { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  | Modified { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  | ModifiedAttributes { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  | Removed { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  -- | Note: Linux-only
+  | WatchedDirectoryRemoved  { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  -- | Note: Linux-only
+  | CloseWrite  { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory }
+  -- | Note: Linux-only
+  | Unknown  { eventPath :: FilePath, eventTime :: UTCTime, eventIsDirectory :: EventIsDirectory, eventString :: String }
+  deriving (Eq, Show)
+
+type EventChannel = Chan Event
+
+type EventCallback = Event -> IO ()
+
+type EventAndActionChannel = Chan (Event, Action)
+
+-- | Method of watching for changes.
+data WatchMode =
+  WatchModePoll {
+    watchModePollInterval :: Int
+    -- ^ Polling interval in microseconds.
+  }
+  -- ^ Detect changes by polling the filesystem. Less efficient and may miss fast changes. Not recommended
+  -- unless you're experiencing problems with 'WatchModeOS' (or 'WatchModeOS' is not supported on your platform).
+#ifdef HAVE_NATIVE_WATCHER
+  | WatchModeOS
+  -- ^ Use OS-specific mechanisms to be notified of changes (inotify on Linux, FSEvents on OSX, etc.).
+  -- Not currently available on e.g. *BSD and Wasm/WASI.
+#endif
+
+data ThreadingMode =
+  SingleThread
+  -- ^ Use a single thread for the entire 'Manager'. Event handler callbacks will run sequentially.
+  | ThreadPerWatch
+  -- ^ Use a single thread for each watch (i.e. each call to 'watchDir', 'watchTree', etc.).
+  -- Callbacks within a watch will run sequentially but callbacks from different watches may be interleaved.
+  | ThreadPerEvent
+  -- ^ Launch a separate thread for every event handler.
+
+-- | Watch configuration.
+data WatchConfig = WatchConfig
+  { confWatchMode :: WatchMode
+    -- ^ Watch mode to use.
+  , confThreadingMode :: ThreadingMode
+    -- ^ Threading mode to use.
+  , confOnHandlerException :: SomeException -> IO ()
+    -- ^ Called when a handler throws an exception.
+  }
+
+type IOEvent = IORef Event
+
+-- | A predicate used to determine whether to act on an event.
+type ActionPredicate = Event -> Bool
+
+-- | An action to be performed in response to an event.
+type Action = Event -> IO ()
+
+-- | A general debouncing function.
+type DebounceFn = Action -> IO Action
+
+-- | Predicate to always act.
+act :: ActionPredicate
+act _ = True
@@ -0,0 +1,72 @@
+--
+-- Copyright (c) 2012 Mark Dittmer - http://www.markdittmer.org
+-- Developed for a Google Summer of Code project - http://gsoc2012.markdittmer.org
+--
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# OPTIONS_GHC -fno-warn-orphans #-}
+
+module System.FSNotify.Win32 (
+  FileListener(..)
+  , NativeManager
+  ) where
+
+import Control.Concurrent
+import Control.Monad (when)
+import Data.Bits
+import qualified Data.Map as Map
+import Data.Time (getCurrentTime, UTCTime)
+import Prelude
+import System.FSNotify.Listener
+import System.FSNotify.Path (canonicalizeDirPath)
+import System.FSNotify.Types
+import System.FilePath
+import qualified System.Win32.Notify as WNo
+
+
+type NativeManager = WNo.WatchManager
+
+-- Win32-notify has (temporarily?) dropped support for Renamed events.
+fsnEvent :: EventIsDirectory -> FilePath -> UTCTime -> WNo.Event -> Event
+fsnEvent isDirectory basedir timestamp (WNo.Created name) = Added (normalise (basedir </> name)) timestamp isDirectory
+fsnEvent isDirectory basedir timestamp (WNo.Modified name) = Modified (normalise (basedir </> name)) timestamp isDirectory
+fsnEvent isDirectory basedir timestamp (WNo.Deleted name) = Removed (normalise (basedir </> name)) timestamp isDirectory
+
+handleWNoEvent :: EventIsDirectory -> FilePath -> ActionPredicate -> EventCallback -> WNo.Event -> IO ()
+handleWNoEvent isDirectory basedir actPred callback inoEvent = do
+  currentTime <- getCurrentTime
+  let event = fsnEvent isDirectory basedir currentTime inoEvent
+  when (actPred event) $ callback event
+
+watchDirectory :: Bool -> WatchConfig -> WNo.WatchManager -> FilePath -> ActionPredicate -> EventCallback -> IO (IO ())
+watchDirectory isRecursive _conf watchManager@(WNo.WatchManager mvarMap) path actPred callback = do
+  path' <- canonicalizeDirPath path
+
+  let fileFlags = foldl (.|.) 0 [WNo.fILE_NOTIFY_CHANGE_FILE_NAME
+                                , WNo.fILE_NOTIFY_CHANGE_SIZE
+                                , WNo.fILE_NOTIFY_CHANGE_ATTRIBUTES]
+  let dirFlags = foldl (.|.) 0 [WNo.fILE_NOTIFY_CHANGE_DIR_NAME]
+
+  -- Start one watch for file events and one for directory events
+  -- (There seems to be no other way to provide isDirectory information)
+  wid1 <- WNo.watchDirectory watchManager path' isRecursive fileFlags (handleWNoEvent IsFile path' actPred callback)
+  wid2 <- WNo.watchDirectory watchManager path' isRecursive dirFlags (handleWNoEvent IsDirectory path' actPred callback)
+
+  -- The StopListening action should make sure to remove the watches from the manager after they're killed.
+  -- Otherwise, a call to killSession would cause us to try to kill them again, resulting in an invalid handle error.
+  return $ do
+    WNo.killWatch wid1
+    modifyMVar_ mvarMap $ \watchMap -> return (Map.delete wid1 watchMap)
+
+    WNo.killWatch wid2
+    modifyMVar_ mvarMap $ \watchMap -> return (Map.delete wid2 watchMap)
+
+instance FileListener WNo.WatchManager () where
+  -- TODO: This should actually lookup a Windows API version and possibly return
+  -- Nothing the calls we need are not available. This will require that API
+  -- version information be exposed by Win32-notify.
+  initSession _ = Right <$> WNo.initWatchManager
+
+  killSession = WNo.killWatchManager
+
+  listen = watchDirectory False
+  listenRecursive = watchDirectory True
@@ -0,0 +1,165 @@
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ImplicitParams #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE MultiWayIf #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
+{-# HLINT ignore "Redundant multi-way if" #-}
+
+module FSNotify.Test.EventTests where
+
+import Control.Exception.Safe (MonadThrow)
+import Control.Monad
+import Control.Monad.IO.Class
+import qualified Data.List as L
+import Data.Monoid
+import Data.Ord (comparing)
+import FSNotify.Test.Util
+import Prelude hiding (FilePath)
+import System.FSNotify
+import System.FilePath
+import System.IO (hPutStr)
+import Test.Sandwich
+import UnliftIO hiding (poll)
+import UnliftIO.Directory
+
+
+eventTests :: (
+  MonadUnliftIO m, MonadThrow m
+  ) => TestFolderGenerator -> ThreadingMode -> SpecFree context m ()
+eventTests testFolderGenerator threadingMode = describe "Tests" $ parallelWithoutDirectory $ do
+  let pollOptions = if haveNativeWatcher then [False, True] else [True]
+
+  forM_ pollOptions $ \poll -> describe (if poll then "Polling" else "Native") $ parallelWithoutDirectory $ do
+    forM_ [False, True] $ \recursive -> describe (if recursive then "Recursive" else "Non-recursive") $ parallelWithoutDirectory $
+      forM_ [False, True] $ \nested -> describe (if nested then "Nested" else "Non-nested") $ parallelWithoutDirectory $
+        eventTests' testFolderGenerator threadingMode poll recursive nested
+
+eventTests' :: (
+  MonadUnliftIO m, MonadThrow m
+  ) => TestFolderGenerator -> ThreadingMode -> Bool -> Bool -> Bool -> SpecFree context m ()
+eventTests' testFolderGenerator threadingMode poll recursive nested = do
+  let withFolder' = withTestFolder testFolderGenerator threadingMode poll recursive nested
+  let withFolder action = withFolder' (const $ return ()) (\() ctx -> action ctx)
+  let waitForEvents getEvents action = waitUntil 5.0 (liftIO getEvents >>= action)
+
+  unless (nested || poll || isMac || isWin) $ it "deletes the watched directory" $ withFolder $ \(TestFolderContext watchedDir _f getEvents _clearEvents) -> do
+    removeDirectory watchedDir
+
+    waitForEvents getEvents $ \case
+      [WatchedDirectoryRemoved {..}] | eventPath `equalFilePath` watchedDir && eventIsDirectory == IsDirectory -> return ()
+      events -> expectationFailure $ "Got wrong events: " <> show events
+
+  it "works with a new file" $ withFolder $ \(TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    let wrapper action = if | isWin -> liftIO (writeFile f "foo") >> action
+                            | otherwise -> withFile f AppendMode $ \_ -> action
+
+    wrapper $
+      waitForEvents getEvents $ \events ->
+        if | nested && not recursive -> events `shouldBe` []
+           | isWin && not poll -> case events of
+               -- On Windows, we sometimes get an extra modified event
+               (sortEvents -> [Added {..}, Modified {}]) | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               _ -> expectationFailure $ "Got wrong events: " <> show events
+           | otherwise -> case events of
+               [Added {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               _ -> expectationFailure $ "Got wrong events: " <> show events
+
+  it "works with a new directory" $ withFolder $ \(TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    createDirectory f
+
+    waitForEvents getEvents $ \events ->
+      if | nested && not recursive -> events `shouldBe` []
+         | otherwise -> case events of
+             [Added {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsDirectory -> return ()
+             _ -> expectationFailure $ "Got wrong events: " <> show events
+
+  it "works with a deleted file" $ withFolder' (\f -> liftIO $ writeFile f "") $ \() (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    removeFile f
+
+    waitForEvents getEvents $ \events ->
+      if | nested && not recursive -> events `shouldBe` []
+         | otherwise -> case events of
+             [Removed {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+             _ -> expectationFailure $ "Got wrong events: " <> show events
+
+  unless isWin $ do
+    it "works if there is bad symlink" $ withFolder' (\f -> liftIO $ createSymLink (f <> ".doesNotExist") f) $ \() (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+      waitForEvents getEvents $ \events -> events `shouldBe` []
+
+  it "works with a deleted directory" $ withFolder' (\f -> liftIO $ createDirectory f) $ \() (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    removeDirectory f
+
+    waitForEvents getEvents $ \events ->
+      if | nested && not recursive -> events `shouldBe` []
+         | otherwise -> case events of
+             [Removed {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsDirectory -> return ()
+             _ -> expectationFailure $ "Got wrong events: " <> show events
+
+  it "works with modified file attributes" $ withFolder' (\f -> liftIO $ writeFile f "") $ \() (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    liftIO $ changeFileAttributes f
+
+    -- This test is disabled when polling because the PollManager only keeps track of
+    -- modification time, so it won't catch an unrelated file attribute change
+    waitForEvents getEvents $ \events ->
+      if | poll -> return ()
+         | nested && not recursive -> events `shouldBe` []
+         | isWin -> case events of
+             [Modified {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+             _ -> expectationFailure $ "Got wrong events: " <> show events
+         | otherwise -> case events of
+             [ModifiedAttributes {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+             _ -> expectationFailure $ "Got wrong events: " <> show events
+
+  it "works with a modified file" $ withFolder' (\f -> liftIO $ writeFile f "") $ \() (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+    (if isWin then withSingleWriteFile f "foo" else withOpenWritableAndWrite f "foo") $
+      waitForEvents getEvents $ \events ->
+        if | nested && not recursive -> events `shouldBe` []
+           | isMac || isFreeBSD -> case events of
+               [Modified {..}] | poll && eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               [ModifiedAttributes {..}] | not poll && eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               _ -> expectationFailure $ "Got wrong events: " <> show events <> " (wanted file path " <> show f <> ")"
+           | otherwise -> case events of
+               [Modified {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               _ -> expectationFailure $ "Got wrong events: " <> show events <> " (wanted file path " <> show f <> ")"
+
+  when (isLinux || isFreeBSD) $ unless poll $ do
+    let setup f = liftIO $ do
+          h <- openFile f WriteMode
+          hPutStr h "asdf" >> hFlush h
+          return h
+    it "gets a close_write" $ withFolder' setup $ \h (TestFolderContext _watchedDir f getEvents _clearEvents) -> do
+      liftIO $ hClose h
+      waitForEvents getEvents $ \events ->
+        if | nested && not recursive -> events `shouldBe` []
+           | otherwise -> case events of
+               [CloseWrite {..}] | eventPath `equalFilePath` f && eventIsDirectory == IsFile -> return ()
+               _ -> expectationFailure $ "Got wrong events: " <> show events
+
+withSingleWriteFile :: MonadIO m => FilePath -> String -> m b -> m b
+withSingleWriteFile fp contents action = do
+  liftIO $ writeFile fp contents
+  action
+
+withOpenWritableAndWrite :: MonadUnliftIO m => FilePath -> String -> m b -> m b
+withOpenWritableAndWrite fp contents action = do
+  withFile fp WriteMode $ \h ->
+    flip finally (hClose h) $ do
+      liftIO $ hPutStr h contents
+      action
+
+sortEvents :: [Event] -> [Event]
+sortEvents = L.sortBy (comparing eventToNum)
+  where
+    eventToNum :: Event -> Int
+    eventToNum (Added {}) = 1
+    eventToNum (Modified {}) = 2
+    eventToNum (ModifiedAttributes {}) = 3
+    eventToNum (Removed {}) = 4
+    eventToNum (WatchedDirectoryRemoved {}) = 5
+    eventToNum (CloseWrite {}) = 6
+    eventToNum (Unknown {}) = 7
@@ -0,0 +1,207 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DataKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE ImplicitParams #-}
+{-# LANGUAGE NumericUnderscores #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE ViewPatterns #-}
+
+module FSNotify.Test.Util where
+
+import Control.Exception.Safe (Handler(..))
+import Control.Monad.Logger
+import Control.Retry
+import Data.String.Interpolate
+import System.FSNotify
+import System.FilePath
+import Test.Sandwich
+import UnliftIO hiding (poll, Handler)
+import UnliftIO.Concurrent
+import UnliftIO.Directory
+
+#if !MIN_VERSION_base(4,11,0)
+import Data.Monoid
+#endif
+
+#ifdef mingw32_HOST_OS
+import Data.Bits
+import System.Win32.File (getFileAttributes, setFileAttributes, fILE_ATTRIBUTE_TEMPORARY)
+import System.Win32.SymbolicLink (createSymbolicLinkFile)
+
+-- Perturb the file's attributes, to check that a modification event is emitted
+changeFileAttributes :: FilePath -> IO ()
+changeFileAttributes file = do
+  attrs <- getFileAttributes file
+  setFileAttributes file (attrs `xor` fILE_ATTRIBUTE_TEMPORARY)
+
+createSymLink :: FilePath -> FilePath -> IO ()
+#if __GLASGOW_HASKELL__ < 900
+createSymLink file1 file2 = createSymbolicLinkFile file1 file2
+#else
+createSymLink file1 file2 = createSymbolicLinkFile file1 file2 True
+#endif
+
+#else
+import System.PosixCompat.Files (touchFile, createSymbolicLink)
+
+changeFileAttributes :: FilePath -> IO ()
+changeFileAttributes = touchFile
+
+createSymLink :: FilePath -> FilePath -> IO ()
+createSymLink = createSymbolicLink
+#endif
+
+
+isMac :: Bool
+#ifdef darwin_HOST_OS
+isMac = True
+#else
+isMac = False
+#endif
+
+isWin :: Bool
+#ifdef mingw32_HOST_OS
+isWin = True
+#else
+isWin = False
+#endif
+
+isLinux :: Bool
+#ifdef linux_HOST_OS
+isLinux = True
+#else
+isLinux = False
+#endif
+
+isFreeBSD :: Bool
+#ifdef freebsd_HOST_OS
+isFreeBSD = True
+#else
+isFreeBSD = False
+#endif
+
+haveNativeWatcher :: Bool
+#ifdef HAVE_NATIVE_WATCHER
+haveNativeWatcher = True
+#else
+haveNativeWatcher = False
+#endif
+
+waitUntil :: MonadUnliftIO m => Double -> m a -> m a
+#if MIN_VERSION_retry(0, 7, 0)
+waitUntil timeInSeconds action = withRunInIO $ \runInIO ->
+  recovering policy [\_ -> Handler handleFn] (\_ -> runInIO action)
+#else
+waitUntil timeInSeconds action = withRunInIO $ \runInIO ->
+  recovering policy [\_ -> Handler handleFn] (runInIO action)
+#endif
+  where
+    handleFn :: SomeException -> IO Bool
+    handleFn (fromException -> Just (_ :: FailureReason)) = return True
+    handleFn _ = return False
+
+    policy = limitRetriesByCumulativeDelay (round (timeInSeconds * 1000000.0)) $ capDelay 1000000 $ exponentialBackoff 1000
+
+
+data TestFolderContext = TestFolderContext {
+  watchedDir :: FilePath
+  , filePath :: FilePath
+  , getEvents :: IO [Event]
+  , clearEvents :: IO ()
+  }
+
+data TestFolderGenerator = TestFolderGenerator {
+  testFolderGeneratorRootDir :: FilePath
+  , testFolderGeneratorId :: MVar Int
+  }
+
+newTestFolderGenerator :: MonadUnliftIO m => FilePath -> m TestFolderGenerator
+newTestFolderGenerator dir = TestFolderGenerator dir <$> newMVar 0
+
+withTestFolderGenerator :: MonadUnliftIO m => (TestFolderGenerator -> m a) -> m a
+withTestFolderGenerator action = do
+  withSystemTempDirectory "hfsnotify-tests" $ \dir ->
+    newTestFolderGenerator dir >>= action
+
+withRandomTempDirectory :: MonadUnliftIO m => TestFolderGenerator -> (FilePath -> m a) -> m a
+withRandomTempDirectory (TestFolderGenerator {..}) action = do
+  testId <- modifyMVar testFolderGeneratorId $ \x ->
+    return (x + 1, x)
+  let dir = testFolderGeneratorRootDir </> ("test_" <> show testId)
+  bracket_ (createDirectory dir)
+           (removePathForcibly dir)
+           (action dir)
+
+withTestFolder :: (
+  MonadUnliftIO m, MonadLogger m
+  )
+  => TestFolderGenerator
+  -> ThreadingMode
+  -> Bool
+  -> Bool
+  -> Bool
+  -> (FilePath -> m b)
+  -> (b -> TestFolderContext -> m a)
+  -> m a
+withTestFolder testFolderGenerator threadingMode poll recursive nested setup action = do
+  withRandomTempDirectory testFolderGenerator $ \watchedDir' -> do
+    info [i|Got temp directory: #{watchedDir'}|]
+    let fileName = "testfile"
+    let baseDir = if nested then watchedDir' </> "subdir" else watchedDir'
+    let watchFn = if recursive then watchTree else watchDir
+
+    createDirectoryIfMissing True baseDir
+
+    let p = normalise $ baseDir </> fileName
+
+    setupResult <- setup p
+
+    let pollInterval = 2 * 10^(5 :: Int)
+
+    -- Delay before starting the watcher to make sure setup events picked up.
+    --
+    -- For MacOS, we can apparently get an event for the creation of "subdir" when doing nested tests,
+    -- even though we create the watcher after this.
+    --
+    -- On Windows, we occasionally see a test flake when there's no pause here.
+    --
+    -- So, let's put a healthy sleep between the setup actions and the watcher initialization.
+    --
+    -- When polling, we want to ensure we wait at least as long as the effective filesystem modification
+    -- time granularity (which on Linux can be on the order of 10 milliseconds), *or*
+    -- the poll interval, whichever is greater.
+    threadDelay (max 5_000_000 (3 * pollInterval))
+
+    let conf = defaultConfig {
+#ifndef HAVE_NATIVE_WATCHER
+          confWatchMode = if poll then WatchModePoll pollInterval else error "No native watcher available."
+#else
+          confWatchMode = if poll then WatchModePoll pollInterval else WatchModeOS
+#endif
+          , confThreadingMode = threadingMode
+          }
+
+    withRunInIO $ \runInIO ->
+      withManagerConf conf $ \mgr -> do
+        eventsVar <- newIORef []
+        bracket
+          (watchFn mgr watchedDir' (const True) (\ev -> atomicModifyIORef eventsVar (\evs -> (ev:evs, ()))))
+          (\stop -> stop)
+          (\_ -> runInIO $ action setupResult $ TestFolderContext {
+            watchedDir = watchedDir'
+            , filePath = p
+            , getEvents = readIORef eventsVar
+            , clearEvents = atomicWriteIORef eventsVar []
+            }
+          )
+
+parallelWithoutDirectory :: SpecFree context m () -> SpecFree context m ()
+parallelWithoutDirectory = parallel' (defaultNodeOptions {
+                                         nodeOptionsCreateFolder = False
+                                         , nodeOptionsVisibilityThreshold = 70
+                                         })
@@ -0,0 +1,50 @@
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ImplicitParams #-}
+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE QuasiQuotes #-}
+
+module Main where
+
+import Control.Monad
+import Control.Monad.IO.Class
+import Data.String.Interpolate
+import FSNotify.Test.EventTests
+import FSNotify.Test.Util
+import Prelude hiding (FilePath)
+import System.FSNotify
+import System.FilePath
+import Test.Sandwich
+import UnliftIO.IORef
+
+
+main :: IO ()
+main =
+  withTestFolderGenerator $ \testFolderGenerator ->
+  runSandwichWithCommandLineArgs defaultOptions $ parallelN 20 $ do
+    describe "Configuration" $ do
+      it "respects the confOnHandlerException option" $ do
+        withRandomTempDirectory testFolderGenerator $ \watchedDir' -> do
+          info [i|Got temp dir: #{watchedDir'}|]
+          exceptions <- newIORef (0 :: Int)
+          let conf = defaultConfig { confOnHandlerException = \_ -> modifyIORef exceptions (+ 1) }
+
+          liftIO $ withManagerConf conf $ \mgr -> do
+            stop <- watchDir mgr watchedDir' (const True) $ \ev -> do
+              case ev of
+#ifdef darwin_HOST_OS
+                Modified {} -> expectationFailure "Oh no!"
+#else
+                Added {} -> expectationFailure "Oh no!"
+#endif
+                _ -> return ()
+
+            writeFile (watchedDir' </> "testfile") "foo"
+
+            waitUntil 5.0 $
+              readIORef exceptions >>= (`shouldBe` 1)
+
+            stop
+
+    describe "SingleThread" $ eventTests testFolderGenerator SingleThread
+    describe "ThreadPerWatch" $ eventTests testFolderGenerator ThreadPerWatch
+    describe "ThreadPerEvent" $ eventTests testFolderGenerator ThreadPerEvent
@@ -0,0 +1,196 @@
+{-# LANGUAGE ForeignFunctionInterface #-}
+#if __GLASGOW_HASKELL__ >= 701
+{-# LANGUAGE InterruptibleFFI #-}
+#endif
+
+{-# LANGUAGE LambdaCase #-}
+
+module System.Win32.FileNotify (
+  Handle
+  , Action(..)
+  , getWatchHandle
+  , readDirectoryChanges
+  ) where
+
+import Data.Char (isSpace)
+import Foreign ((.|.), Ptr, FunPtr, alloca, allocaBytes, castPtr, nullFunPtr, peekByteOff, plusPtr)
+import Foreign.C (peekCWStringLen)
+import Numeric (showHex)
+import System.Win32.File (
+  FileNotificationFlag
+  , LPOVERLAPPED
+  , createFile
+  , oPEN_EXISTING
+  , fILE_FLAG_BACKUP_SEMANTICS
+  , fILE_LIST_DIRECTORY
+  , fILE_SHARE_READ
+  , fILE_SHARE_WRITE
+  )
+import System.Win32.Types (
+  BOOL
+  , DWORD
+  , ErrCode
+  , HANDLE
+  , LPDWORD
+  , LPVOID
+  , getErrorMessage
+  , getLastError
+  , localFree
+  , nullPtr
+  )
+import System.Win32.Types (peekTString)
+
+
+#include <windows.h>
+
+type Handle = HANDLE
+
+getWatchHandle :: FilePath -> IO Handle
+getWatchHandle dir = createFile dir
+  fILE_LIST_DIRECTORY -- Access mode
+  (fILE_SHARE_READ .|. fILE_SHARE_WRITE) -- Share mode
+  Nothing -- security attributes
+  oPEN_EXISTING -- Create mode, we want to look at an existing directory
+  fILE_FLAG_BACKUP_SEMANTICS -- File attribute, nb NOT using OVERLAPPED since we work synchronously
+  Nothing -- No template file
+
+
+readDirectoryChanges :: Handle -> Bool -> FileNotificationFlag -> IO (Either (ErrCode, String) [(Action, String)])
+readDirectoryChanges h watchSubTree mask = do
+  let maxBuf = 16384
+  allocaBytes maxBuf $ \buffer -> do
+    alloca $ \bret -> do
+      readDirectoryChangesW h buffer (toEnum maxBuf) watchSubTree mask bret >>= \case
+        Left err -> return $ Left err
+        Right () -> Right <$> readChanges buffer
+
+data Action = FileAdded | FileRemoved | FileModified | FileRenamedOld | FileRenamedNew
+  deriving (Show, Read, Eq, Ord, Enum)
+
+readChanges :: Ptr FILE_NOTIFY_INFORMATION -> IO [(Action, String)]
+readChanges pfni = do
+  fni <- peekFNI pfni
+  let entry = (faToAction $ fniAction fni, fniFileName fni)
+      nioff = fromEnum $ fniNextEntryOffset fni
+  entries <- if nioff == 0 then return [] else readChanges $ pfni `plusPtr` nioff
+  return $ entry:entries
+
+faToAction :: FileAction -> Action
+faToAction fa = toEnum $ fromEnum fa - 1
+
+-------------------------------------------------------------------
+-- Low-level stuff that binds to notifications in the Win32 API
+
+-- Defined in System.Win32.File, but with too few cases:
+-- type AccessMode = UINT
+
+#if !(MIN_VERSION_Win32(2,4,0))
+#{enum AccessMode,
+ , fILE_LIST_DIRECTORY = FILE_LIST_DIRECTORY
+ }
+-- there are many more cases but I only need this one.
+#endif
+
+type FileAction = DWORD
+
+#{enum FileAction,
+ , _fILE_ACTION_ADDED            = FILE_ACTION_ADDED
+ , _fILE_ACTION_REMOVED          = FILE_ACTION_REMOVED
+ , _fILE_ACTION_MODIFIED         = FILE_ACTION_MODIFIED
+ , _fILE_ACTION_RENAMED_OLD_NAME = FILE_ACTION_RENAMED_OLD_NAME
+ , _fILE_ACTION_RENAMED_NEW_NAME = FILE_ACTION_RENAMED_NEW_NAME
+ }
+
+-- type WCHAR = Word16
+
+-- This is a bit overkill for now, I'll only use nullFunPtr anyway,
+-- but who knows, maybe someday I'll want asynchronous callbacks on the OS level.
+type LPOVERLAPPED_COMPLETION_ROUTINE = FunPtr ((DWORD, DWORD, LPOVERLAPPED) -> IO ())
+
+data FILE_NOTIFY_INFORMATION = FILE_NOTIFY_INFORMATION
+    { fniNextEntryOffset, fniAction :: DWORD
+    , fniFileName :: String
+    }
+
+-- instance Storable FILE_NOTIFY_INFORMATION where
+-- ... well, we can't write an instance since the struct is not of fix size,
+-- so we'll have to do it the hard way, and not get anything for free. Sigh.
+
+-- sizeOfFNI :: FILE_NOTIFY_INFORMATION -> Int
+-- sizeOfFNI fni =  (#size FILE_NOTIFY_INFORMATION) + (#size WCHAR) * (length (fniFileName fni) - 1)
+
+peekFNI :: Ptr FILE_NOTIFY_INFORMATION -> IO FILE_NOTIFY_INFORMATION
+peekFNI buf = do
+  neof <- (#peek FILE_NOTIFY_INFORMATION, NextEntryOffset) buf
+  acti <- (#peek FILE_NOTIFY_INFORMATION, Action) buf
+  fnle <- (#peek FILE_NOTIFY_INFORMATION, FileNameLength) buf
+  fnam <- peekCWStringLen
+            (buf `plusPtr` (#offset FILE_NOTIFY_INFORMATION, FileName), -- start of array
+            fromEnum (fnle :: DWORD) `div` 2 ) -- fnle is the length in *bytes*, and a WCHAR is 2 bytes
+  return $ FILE_NOTIFY_INFORMATION neof acti fnam
+
+
+readDirectoryChangesW :: Handle -> Ptr FILE_NOTIFY_INFORMATION -> DWORD -> BOOL -> FileNotificationFlag -> LPDWORD -> IO (Either (ErrCode, String) ())
+readDirectoryChangesW h buf bufSize watchSubTree f br =
+  c_ReadDirectoryChangesW h (castPtr buf) bufSize watchSubTree f br nullPtr nullFunPtr >>= \case
+    True -> return $ Right ()
+    False -> do
+      -- Extract the failure message, as done in https://hackage.haskell.org/package/Win32-2.14.0.0/docs/src/System.Win32.WindowsString.Types.html#errorWin
+      err_code <- getLastError
+      msg <- getErrorMessage err_code >>= \case
+        x | x == nullPtr -> return $ "Error 0x" ++ Numeric.showHex err_code ""
+        c_msg -> do
+          msg <- peekTString c_msg
+          -- We ignore failure of freeing c_msg, given we're already failing
+          _ <- localFree c_msg
+          return msg
+      let msg' = reverse $ dropWhile isSpace $ reverse msg -- drop trailing \n
+      return $ Left (err_code, msg')
+
+{-
+asynchReadDirectoryChangesW :: Handle -> Ptr FILE_NOTIFY_INFORMATION -> DWORD -> BOOL -> FileNotificationFlag
+                                -> LPOVERLAPPED -> IO ()
+asynchReadDirectoryChangesW h buf bufSize watchSubTree f over =
+  failIfFalse_ "ReadDirectoryChangesW" $ c_ReadDirectoryChangesW h (castPtr buf) bufSize watchSubTree f nullPtr over nullFunPtr
+
+cbReadDirectoryChangesW :: Handle -> Ptr FILE_NOTIFY_INFORMATION -> DWORD -> BOOL -> FileNotificationFlag
+                                -> LPOVERLAPPED -> IO BOOL
+cbReadDirectoryChanges
+-}
+
+-- The interruptible qualifier will keep threads listening for events from hanging blocking when killed
+#if __GLASGOW_HASKELL__ >= 701
+foreign import stdcall interruptible "windows.h ReadDirectoryChangesW"
+#else
+foreign import stdcall safe "windows.h ReadDirectoryChangesW"
+#endif
+  c_ReadDirectoryChangesW :: Handle -> LPVOID -> DWORD -> BOOL -> DWORD -> LPDWORD -> LPOVERLAPPED -> LPOVERLAPPED_COMPLETION_ROUTINE -> IO BOOL
+
+{-
+type CompletionRoutine :: (DWORD, DWORD, LPOVERLAPPED) -> IO ()
+foreign import ccall "wrapper"
+    mkCompletionRoutine :: CompletionRoutine -> IO (FunPtr CompletionRoutine)
+
+type LPOVERLAPPED = Ptr OVERLAPPED
+type LPOVERLAPPED_COMPLETION_ROUTINE = FunPtr CompletionRoutine
+
+data OVERLAPPED = OVERLAPPED
+    {
+    }
+
+
+-- In System.Win32.File, but missing a crucial case:
+-- type FileNotificationFlag = DWORD
+-}
+
+-- See https://msdn.microsoft.com/en-us/library/windows/desktop/aa365465(v=vs.85).aspx
+#{enum FileNotificationFlag,
+ , _fILE_NOTIFY_CHANGE_FILE_NAME = FILE_NOTIFY_CHANGE_FILE_NAME
+ , _fILE_NOTIFY_CHANGE_DIR_NAME = FILE_NOTIFY_CHANGE_DIR_NAME
+ , _fILE_NOTIFY_CHANGE_ATTRIBUTES = FILE_NOTIFY_CHANGE_ATTRIBUTES
+ , _fILE_NOTIFY_CHANGE_SIZE = FILE_NOTIFY_CHANGE_SIZE
+ , _fILE_NOTIFY_CHANGE_LAST_WRITE = FILE_NOTIFY_CHANGE_LAST_WRITE
+ , _fILE_NOTIFY_CHANGE_LAST_ACCESS = FILE_NOTIFY_CHANGE_LAST_ACCESS
+ , _fILE_NOTIFY_CHANGE_CREATION = FILE_NOTIFY_CHANGE_CREATION
+ , _fILE_NOTIFY_CHANGE_SECURITY = FILE_NOTIFY_CHANGE_SECURITY
+ }
@@ -0,0 +1,123 @@
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE QuasiQuotes #-}
+
+module System.Win32.Notify (
+  Event(..)
+  , EventVariety(..)
+  , Handler
+  , WatchId(..)
+  , WatchManager(..)
+  , initWatchManager
+  , killWatch
+  , killWatchManager
+  , watch
+  , watchDirectory
+
+  , fILE_NOTIFY_CHANGE_FILE_NAME
+  , fILE_NOTIFY_CHANGE_DIR_NAME
+  , fILE_NOTIFY_CHANGE_ATTRIBUTES
+  , fILE_NOTIFY_CHANGE_SIZE
+  , fILE_NOTIFY_CHANGE_LAST_WRITE
+  -- , fILE_NOTIFY_CHANGE_LAST_ACCESS
+  -- , fILE_NOTIFY_CHANGE_CREATION
+  , fILE_NOTIFY_CHANGE_SECURITY
+  ) where
+
+import Control.Concurrent
+import Control.Exception.Safe (SomeException, catch, throwIO)
+import Control.Monad (forM_, forever)
+import Data.Function (fix)
+import Data.Map (Map)
+import qualified Data.Map as Map
+import Foreign.C.Error (errnoToIOError)
+import System.FilePath
+import System.IO.Error (ioeSetErrorString)
+import System.Win32.File
+import System.Win32.FileNotify
+import System.Win32.Types (c_maperrno_func)
+
+
+data EventVariety =
+  Modify
+  | Create
+  | Delete
+  | Move
+  deriving Eq
+
+data Event
+  -- | A file was modified. @Modified isDirectory file@
+  = Modified { filePath :: FilePath }
+  -- | A file was created. @Created isDirectory file@
+  | Created { filePath :: FilePath }
+  -- | A file was deleted. @Deleted isDirectory file@
+  | Deleted { filePath :: FilePath }
+  deriving (Eq, Show)
+
+type Handler = Event -> IO ()
+
+data WatchId = WatchId [ThreadId] Handle deriving (Eq, Ord, Show)
+type WatchMap = Map WatchId Handler
+data WatchManager = WatchManager { watchManagerWatchMap :: MVar WatchMap }
+
+initWatchManager :: IO WatchManager
+initWatchManager = WatchManager <$> newMVar Map.empty
+
+killWatchManager :: WatchManager -> IO ()
+killWatchManager (WatchManager mvarMap) = do
+  modifyMVar_ mvarMap $ \watchMap -> do
+    forM_ (Map.keys watchMap) killWatch
+    return mempty
+
+watchDirectory :: WatchManager -> FilePath -> Bool -> FileNotificationFlag -> Handler -> IO WatchId
+watchDirectory (WatchManager mvarMap) dir watchSubTree flags handler = do
+  watchHandle <- getWatchHandle dir
+  chanEvents <- newChan
+  tid1 <- forkIO $ dispatcher chanEvents
+  tid2 <- forkIO $ osEventsReader dir watchSubTree flags watchHandle chanEvents
+  let wid = WatchId [tid1, tid2] watchHandle
+  modifyMVar mvarMap $ \watchMap ->
+    return (Map.insert wid handler watchMap, wid)
+
+  where
+    dispatcher :: Chan [Event] -> IO ()
+    dispatcher chanEvents = forever $ readChan chanEvents >>= mapM_ handler
+
+watch :: WatchManager -> FilePath -> Bool -> FileNotificationFlag -> IO (WatchId, Chan [Event])
+watch (WatchManager mvarMap) dir watchSubTree flags = do
+  watchHandle <- getWatchHandle dir
+  chanEvents <- newChan
+  tid <- forkIO $ osEventsReader dir watchSubTree flags watchHandle chanEvents
+  let wid = WatchId [tid] watchHandle
+  modifyMVar_ mvarMap $ \watchMap ->
+    return (Map.insert wid (const $ return ()) watchMap)
+  return (wid, chanEvents)
+
+osEventsReader :: FilePath -> Bool -> FileNotificationFlag -> Handle -> Chan [Event] -> IO ()
+osEventsReader dir watchSubTree flags watchHandle chanEvents = fix $ \loop ->
+  readDirectoryChanges watchHandle watchSubTree flags >>= \case
+    -- ERROR_OPERATION_ABORTED: this happens when the event read thread is killed.
+    -- https://learn.microsoft.com/en-us/windows/win32/debug/system-error-codes--500-999-
+    -- Just return silently.
+    Left (995, _) -> return ()
+    Left (err_code, msg) -> do
+      errno <- c_maperrno_func err_code
+      throwIO (errnoToIOError "ReadDirectoryChangesW" errno Nothing Nothing `ioeSetErrorString` msg)
+    Right events -> actsToEvents dir events >>= writeChan chanEvents >> loop
+
+killWatch :: WatchId -> IO ()
+killWatch (WatchId tids handle) = do
+  forM_ tids killThread
+  -- catch (closeHandle handle) $ \(e :: SomeException) ->
+  --   putStrLn ([i|Failed to kill watch #{handle}: #{e}|])
+  catch (closeHandle handle) $ \(_ :: SomeException) -> return ()
+
+actsToEvents :: FilePath -> [(Action, String)] -> IO [Event]
+actsToEvents baseDir = mapM actToEvent
+  where
+    actToEvent (act, fn) = do
+      case act of
+        FileModified -> return $ Modified $ baseDir </> fn
+        FileAdded -> return $ Created $ baseDir </> fn
+        FileRemoved -> return $ Deleted $ baseDir </> fn
+        FileRenamedOld -> return $ Deleted $ baseDir </> fn
+        FileRenamedNew -> return $ Created $ baseDir </> fn
@@ -1,5 +1,5 @@
-module Converge
-  ( -- * Core types
+module Converge (
+    -- * Core types
    Options (..),
    RepoConfig (..),
    defaultOptions,
@@ -31,11 +31,10 @@ import Data.Maybe (fromMaybe)
 import Data.Text (Text)
 import qualified Data.Text as T
 import Data.Yaml (FromJSON (..), decodeFileThrow, withObject, (.:), (.:?))
-import GHC.Generics (Generic)
 import System.Directory (getCurrentDirectory)
 import System.Exit (ExitCode (..))
-import System.FilePath (isAbsolute, (</>))
 import System.FSNotify
+import System.FilePath (isAbsolute, (</>))
 import System.IO (hPutStrLn, stderr)
 import System.Process (readProcessWithExitCode, spawnProcess)

@@ -88,7 +87,7 @@ data Config = Config
    { cfgRepos :: ![RepoConfig]
    , cfgDebounceMs :: !(Maybe Int)
    }
-  deriving (Show, Eq, Generic)
+    deriving (Show, Eq)

 instance FromJSON Config where
    parseJSON = withObject "Config" $ \o ->
@@ -100,8 +99,8 @@ instance FromJSON RepoConfig where
    parseJSON = withObject "RepoConfig" $ \o ->
        RepoConfig
            <$> o .: "path"
-      <*> o .:? "remote" .!= "origin"
-      <*> o .:? "branch" .!= "main"
+            <*> (fromMaybe "origin" <$> o .:? "remote")
+            <*> (fromMaybe "main" <$> o .:? "branch")

 -- | Load a YAML config file.
 loadConfig :: FilePath -> IO Config
@@ -129,7 +128,7 @@ watchRepo opts repo = do
    absPath <- resolvePath (rcPath repo)
    let debounceUs = optDebounceMs opts * 1000
    bracket
-    (startManagerConf defaultConfig {confDebounce = NoDebounce})
+        (startManagerConf defaultConfig)
        stopManager
        $ \mgr -> do
            _ <- watchDir mgr absPath (const True) $ \_event -> do
@@ -169,7 +168,8 @@ gitCommitAll repoPath = do
 -- | Pull from the configured remote and branch.
 gitPull :: RepoConfig -> IO (ExitCode, Text, Text)
 gitPull repo =
-  runGitIn (rcPath repo)
+    runGitIn
+        (rcPath repo)
        ["pull", "--no-edit", T.unpack (rcRemote repo), T.unpack (rcBranch repo)]

 -- | Check if the repository currently has merge conflicts.
@@ -187,7 +187,9 @@ notifyConflict :: Options -> RepoConfig -> IO ()
 notifyConflict opts repo = do
    let cmd = T.unpack (optNotifyCmd opts)
        title = "Converge: Merge Conflict"
-      body = "A merge conflict occurred in " <> T.pack (rcPath repo)
+        body =
+            "A merge conflict occurred in "
+                <> T.pack (rcPath repo)
                <> ". Manual resolution required."
    _ <- spawnProcess cmd ["--urgency=critical", title, T.unpack body]
    pure ()
@@ -198,5 +200,5 @@ notifyConflict opts repo = do

 runGitIn :: FilePath -> [String] -> IO (ExitCode, Text, Text)
 runGitIn repoPath args = do
-  (code, out, err) <- readProcessWithExitCode "git" args ""
+    (code, out, err) <- readProcessWithExitCode "git" ("-C" : repoPath : args) ""
    pure (code, T.pack out, T.pack err)
@@ -0,0 +1,12 @@
+# This file was autogenerated by Stack.
+# You should not edit this file by hand.
+# For more information, please see the documentation at:
+#   https://docs.haskellstack.org/en/stable/topics/lock_files
+
+packages: []
+snapshots:
+- completed:
+    sha256: abc790b571e0c70e929db74b329e3c18d7e76a6e173e8bdf94f1ba20770d4c24
+    size: 728990
+    url: https://raw.githubusercontent.com/commercialhaskell/stackage-snapshots/master/lts/24/38.yaml
+  original: lts-24.38