feat(engine): refactor funnel to allow skipping of events

espanso-engine/src/funnel/default.rs

@@ -48,7 +48,10 @@ impl<'a> Funnel for DefaultFunnel<'a> {
       .expect("invalid source index returned by select operation");
 
     // Receive (and convert) the event
-    let event = source.receive(op);
+    if let Some(event) = source.receive(op) {
       FunnelResult::Event(event)
+    } else {
+      FunnelResult::Skipped
+    }
   }
 }

espanso-engine/src/funnel/mod.rs

@@ -27,7 +27,7 @@ mod default;
 
 pub trait Source<'a> {
   fn register(&'a self, select: &mut Select<'a>) -> usize;
-  fn receive(&'a self, op: SelectedOperation) -> Event;
+  fn receive(&'a self, op: SelectedOperation) -> Option<Event>;
 }
 
 pub trait Funnel {
@@ -36,6 +36,7 @@ pub trait Funnel {
 
 pub enum FunnelResult {
   Event(Event),
+  Skipped,
   EndOfStream,
 }
 

espanso-engine/src/lib.rs

@@ -68,6 +68,9 @@ impl<'a> Engine<'a> {
           debug!("end of stream received");
           return ExitMode::Exit;
         }
+        FunnelResult::Skipped => {
+          // This event has been skipped, no need to handle it
+        }
       }
     }
   }