Tolerate changes in the state file

src/watch/notify_event.rs

@@ -0,0 +1,42 @@
+use notify_debouncer_mini::{DebounceEventResult, DebouncedEventKind};
+use std::{path::Path, sync::mpsc::Sender};
+
+use super::WatchEvent;
+
+pub struct DebounceEventHandler {
+    pub tx: Sender<WatchEvent>,
+    pub exercise_paths: &'static [&'static Path],
+}
+
+impl notify_debouncer_mini::DebounceEventHandler for DebounceEventHandler {
+    fn handle_event(&mut self, event: DebounceEventResult) {
+        let event = match event {
+            Ok(event) => {
+                let Some(exercise_ind) = event
+                    .iter()
+                    .filter_map(|event| {
+                        if event.kind != DebouncedEventKind::Any
+                            || !event.path.extension().is_some_and(|ext| ext == "rs")
+                        {
+                            return None;
+                        }
+
+                        self.exercise_paths
+                            .iter()
+                            .position(|path| event.path.ends_with(path))
+                    })
+                    .min()
+                else {
+                    return;
+                };
+
+                WatchEvent::FileChange { exercise_ind }
+            }
+            Err(e) => WatchEvent::NotifyErr(e),
+        };
+
+        // An error occurs when the receiver is dropped.
+        // After dropping the receiver, the debouncer guard should also be dropped.
+        let _ = self.tx.send(event);
+    }
+}