Don't skip exercises on file changes

src/app_state.rs

@@ -198,6 +198,10 @@ impl AppState {
     }
 
     pub fn set_current_exercise_ind(&mut self, exercise_ind: usize) -> Result<()> {
+        if exercise_ind == self.current_exercise_ind {
+            return Ok(());
+        }
+
         if exercise_ind >= self.exercises.len() {
             bail!(BAD_INDEX_ERR);
         }

src/watch.rs

@@ -95,7 +95,7 @@ pub fn watch(
             WatchEvent::Input(InputEvent::Run) => watch_state.run_current_exercise()?,
             WatchEvent::Input(InputEvent::Unrecognized) => watch_state.render()?,
             WatchEvent::FileChange { exercise_ind } => {
-                watch_state.run_exercise_with_ind(exercise_ind)?;
+                watch_state.handle_file_change(exercise_ind)?;
             }
             WatchEvent::TerminalResize => {
                 watch_state.render()?;

src/watch/state.rs

@@ -72,7 +72,14 @@ impl<'a> WatchState<'a> {
         self.render()
     }
 
-    pub fn run_exercise_with_ind(&mut self, exercise_ind: usize) -> Result<()> {
+    pub fn handle_file_change(&mut self, exercise_ind: usize) -> Result<()> {
+        // Don't skip exercises on file changes to avoid confusion from missing exercises.
+        // Skipping exercises must be explicit in the interactive list.
+        // But going back to an earlier exercise on file change is fine.
+        if self.app_state.current_exercise_ind() < exercise_ind {
+            return Ok(());
+        }
+
         self.app_state.set_current_exercise_ind(exercise_ind)?;
         self.run_current_exercise()
     }