PollWatcher panics if a watched file is removed and recreated.

[jhscheer]

System details

• OS/Platform name and version: Linux (5.13.15-200.fc34.x86_64)
• Rust version (if building from source): rustc --version: 1.54.0
• Notify version (or commit hash if building from git): 4.0.17 / 5.0.0-pre.13

What you did (as detailed as you can)

fn watch<P: AsRef<Path>>(path: P) -> notify::Result<()> {                                                                                          
    let (tx, rx) = channel();                                                                                                                      
                                                                                                                                                                                                                              
    // let mut watcher = PollWatcher::new(tx, Duration::from_secs(1)).unwrap();                                                                    
    let mut watcher = PollWatcher::with_delay_ms(tx, 1000).unwrap();                                                                               
                                                                                                                                                                                                                                                          
    watcher.watch(path.as_ref(), RecursiveMode::NonRecursive)?;                                                                                    
                                                                                                                                                   
    loop {                                                                                                                                         
        match rx.recv() {                                                                                                                          
            Ok(event) => println!("{:?}\n", event),                                                                                                                                                                                                  
            Err(e) => println!("watch error: {:?}", e),                                                                                            
        }                                                                                                                                          
    }                                                                                                                                              
} 

Run above code to monitor testfile, then run:

rm testfile && sleep 1 && touch testfile

Both the raw PollWatcher and the debounced PollWatcher panic if a watched file is remove and recreated.

Edit:
Same issue exists on 5.0.0-pre.13:

let event_handler = Arc::new(Mutex::new(tx));
let mut watcher = PollWatcher::with_delay(event_handler, Duration::from_secs(1))?;

watch error: Error { kind: Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), paths: ["testfile"] }
Event { kind: Remove(Any), paths: ["testfile"], attr:tracker: None, attr:flag: None, attr:info: None, attr:source: None }

watch error: Error { kind: Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), paths: ["testfile"] }
thread '<unnamed>' panicked at 'internal error: entered unreachable code', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/notify-5.0.0-pre.13/src/poll.rs:108:45

What you expected

NoticeRemove("testfile")
Remove("testfile")

RawEvent { path: Some("testfile"), op: Ok(REMOVE), cookie: None }

What happened

Error(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), Some("testfile"))

NoticeRemove("testfile")

Remove("testfile")

Error(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), Some("testfile"))

Error(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), Some("testfile"))

thread '<unnamed>' panicked at 'internal error: entered unreachable code', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/notify-4.0.17/src/poll.rs:97:45

RawEvent { path: Some("testfile"), op: Err(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" })), cookie: None }

RawEvent { path: Some("testfile"), op: Ok(REMOVE), cookie: None }

RawEvent { path: Some("testfile"), op: Err(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" })), cookie: None }

RawEvent { path: Some("testfile"), op: Err(Io(Os { code: 2, kind: NotFound, message: "No such file or directory" })), cookie: None }

thread '<unnamed>' panicked at 'internal error: entered unreachable code', ~/.cargo/registry/src/github.com-1ecc6299db9ec823/notify-4.0.17/src/poll.rs:97:45

[visig9]

This code can reproduce bug.

//! # Dependencies
//!
//! ```toml
//! [dependencies]
//! notify = "5.0.0-pre.15"
//! ```
//!
//! # Test
//!
//! Panic with following shell command.
//!
//! ```sh
//! # in first terminal
//! touch mew.txt
//! cargo run
//!
//! # in second terminal
//! rm mew.txt && sleep 1 && touch mew.txt
//! ```

use notify::Watcher;
use std::{thread, time::Duration};

fn main() {
    let mut watcher = notify::PollWatcher::with_config(
        |event| println!("{event:?}"),
        notify::poll::PollWatcherConfig {
            poll_interval: Duration::from_secs(1),
            ..Default::default()
        },
    )
    .unwrap();

    watcher
        .watch("mew.txt".as_ref(), notify::RecursiveMode::Recursive)
        .unwrap();

    thread::park();
}

Output:

Err(Error { kind: Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), paths: ["mew.txt"] })
Ok(Event { kind: Remove(Any), paths: ["mew.txt"], attr:tracker: None, attr:flag: None, attr:info: None, attr:source: None })
thread 'notify-rs poll loop' panicked at 'internal error: entered unreachable code', /home/visig/.cargo/registry/src/github.com-1ecc6299db9ec823/notify-5.0.0-pre.15/src/poll.rs:206:49
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[visig9]

I create #406 to fix. After this PR, the previous test code should output:

Err(Error { kind: Io(Os { code: 2, kind: NotFound, message: "No such file or directory" }), paths: ["mew.txt"] })
Ok(Event { kind: Remove(Any), paths: ["mew.txt"], attr:tracker: None, attr:flag: None, attr:info: None, attr:source: None })
Ok(Event { kind: Create(Any), paths: ["mew.txt"], attr:tracker: None, attr:flag: None, attr:info: None, attr:source: None })