Check for errors from str_path_to_cfstring_ref.

Closes #301.

src/fsevent.rs

@@ -281,6 +281,10 @@ impl FsEventWatcher {
         unsafe {
             let mut err: cf::CFErrorRef = ptr::null_mut();
             let cf_path = cf::str_path_to_cfstring_ref(str_path, &mut err);
+            if cf_path.is_null() {
+                cf::CFRelease(err as cf::CFRef);
+                return Err(Error::watch_not_found().add_path(path.as_ref().into()));
+            }
 
             let mut to_remove = Vec::new();
             for idx in 0..cf::CFArrayGetCount(self.paths) {
@@ -320,6 +324,12 @@ impl FsEventWatcher {
         unsafe {
             let mut err: cf::CFErrorRef = ptr::null_mut();
             let cf_path = cf::str_path_to_cfstring_ref(str_path, &mut err);
+            if cf_path.is_null() {
+                // Most likely the directory was deleted, or permissions changed,
+                // while the above code was running.
+                cf::CFRelease(err as cf::CFRef);
+                return Err(Error::path_not_found().add_path(path.as_ref().into()));
+            }
             cf::CFArrayAppendValue(self.paths, cf_path);
             cf::CFRelease(cf_path);
         }

tests/race-with-remove-dir.rs

@@ -0,0 +1,28 @@
+use std::{env, fs, thread, time::Duration};
+
+use notify::{immediate_watcher, RecursiveMode, Watcher};
+
+/// Test for <https://github.com/notify-rs/notify/issues/301>.
+/// Note: This test will fail if your temp directory is not writable.
+#[test]
+fn test_race_with_remove_dir() {
+    let tmpdir = env::temp_dir().join(".tmprPcUcB");
+    fs::create_dir_all(&tmpdir).unwrap();
+
+    {
+        let tmpdir = tmpdir.clone();
+        thread::spawn(move || {
+            let mut watcher = immediate_watcher(move |result| {
+                eprintln!("received event: {:?}", result);
+            })
+            .unwrap();
+
+            watcher.watch(tmpdir, RecursiveMode::NonRecursive).unwrap();
+        });
+    }
+
+    let subdir = tmpdir.join("146d921d.tmp");
+    fs::create_dir_all(&subdir).unwrap();
+    fs::remove_dir_all(&tmpdir).unwrap();
+    thread::sleep(Duration::from_secs(1));
+}