Add Watcher::kind()

Note that non-boxing would require an enum that matches the CFG chaos of RecommendedWatcher, adding an enum for every possible configurable watcher combination. And otherwise we'll have to add the specific config calls to the trait.

Closes #361

Cargo.toml

@@ -63,5 +63,6 @@ notify = { path = "." }
 [workspace]
 members = [
   ".",
-  "examples/hot_reload_tide"
+  "examples/hot_reload_tide",
+  "examples/watcher_kind"
 ]

examples/watcher_kind/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "watcher_kind"
+version = "0.1.0"
+authors = ["Aron Heinecke <aron.heinecke@t-online.de>"]
+edition = "2018"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+notify = { version = "5.0.0-pre.13", path = "../../" }

examples/watcher_kind/src/main.rs

@@ -0,0 +1,11 @@
+use std::time::Duration;
+
+use notify::*;
+fn main() {
+    let (tx, rx) = std::sync::mpsc::channel();
+    let watcher: Box<dyn Watcher> = if RecommendedWatcher::kind() == WatcherKind::PollWatcher {
+        Box::new(PollWatcher::with_delay(tx,Duration::from_secs(1)).unwrap())
+    } else {
+        Box::new(RecommendedWatcher::new(tx).unwrap())
+    };
+}

src/fsevent.rs

@@ -542,6 +542,10 @@ impl Watcher for FsEventWatcher {
         self.configure_raw_mode(config, tx);
         rx.recv()?
     }
+
+    fn kind() -> crate::WatcherKind {
+        crate::WatcherKind::Fsevent
+    }
 }
 
 impl Drop for FsEventWatcher {

src/inotify.rs

@@ -619,6 +619,10 @@ impl Watcher for INotifyWatcher {
         self.waker.wake()?;
         rx.recv()?
     }
+
+    fn kind() -> crate::WatcherKind {
+        crate::WatcherKind::Inotify
+    }
 }
 
 impl Drop for INotifyWatcher {

src/kqueue.rs

@@ -386,6 +386,10 @@ impl Watcher for KqueueWatcher {
     fn unwatch(&mut self, path: &Path) -> Result<()> {
         self.unwatch_inner(path)
     }
+
+    fn kind() -> crate::WatcherKind {
+        crate::WatcherKind::Kqueue
+    }
 }
 
 impl Drop for KqueueWatcher {

src/lib.rs

@@ -185,6 +185,24 @@ impl EventHandler for std::sync::mpsc::Sender<Result<Event>> {
     }
 }
 
+/// Watcher kind enumeration
+#[derive(Debug,PartialEq,Eq)]
+#[non_exhaustive]
+pub enum WatcherKind {
+    /// inotify backend (linux)
+    Inotify,
+    /// FS-Event backend (mac)
+    Fsevent,
+    /// KQueue backend (bsd,mac)
+    Kqueue,
+    /// Polling based backend (fallback)
+    PollWatcher,
+    /// Windows backend
+    ReadDirectoryChangesWatcher,
+    /// Fake watcher for testing
+    NullWatcher,
+}
+
 /// Type that can deliver file activity notifications
 ///
 /// Watcher is implemented per platform using the best implementation available on that platform.
@@ -232,6 +250,9 @@ pub trait Watcher {
     fn configure(&mut self, _option: Config) -> Result<bool> {
         Ok(false)
     }
+
+    /// Returns the watcher kind, allowing to perform backend-specific tasks
+    fn kind() -> WatcherKind where Self: Sized;
 }
 
 /// The recommended `Watcher` implementation for the current platform

src/null.rs

@@ -22,4 +22,8 @@ impl Watcher for NullWatcher {
     fn new<F: crate::EventHandler>(event_handler: F) -> Result<Self> where Self: Sized {
         Ok(NullWatcher)
     }
+
+    fn kind() -> crate::WatcherKind {
+        crate::WatcherKind::NullWatcher
+    }
 }

src/poll.rs

@@ -288,6 +288,10 @@ impl Watcher for PollWatcher {
     fn unwatch(&mut self, path: &Path) -> Result<()> {
         self.unwatch_inner(path)
     }
+
+    fn kind() -> crate::WatcherKind {
+        crate::WatcherKind::PollWatcher
+    }
 }
 
 impl Drop for PollWatcher {

src/windows.rs

@@ -15,7 +15,7 @@ use winapi::um::synchapi;
 use winapi::um::winbase::{self, INFINITE, WAIT_OBJECT_0};
 use winapi::um::winnt::{self, FILE_NOTIFY_INFORMATION, HANDLE};
 
-use crate::event::*;
+use crate::{WatcherKind, event::*};
 use crate::{Config, Error, EventHandler, RecursiveMode, Result, Watcher};
 use crossbeam_channel::{bounded, unbounded, Receiver, Sender};
 use std::collections::HashMap;
@@ -512,6 +512,10 @@ impl Watcher for ReadDirectoryChangesWatcher {
         self.tx.send(Action::Configure(config, tx))?;
         rx.recv()?
     }
+
+    fn kind() -> crate::WatcherKind {
+        WatcherKind::ReadDirectoryChangesWatcher
+    }
 }
 
 impl Drop for ReadDirectoryChangesWatcher {