fix: end a drag the compositor never took over

src/dnd.rs

@@ -56,6 +56,14 @@ pub enum AfterDrag {
     SlideOut,
 }
 
+/// During a real drag the compositor owns the pointer and the origin gets
+/// no button events. A release that reaches the dragged thumbnail means the
+/// compositor never took the drag over (e.g. a flick released before the
+/// drag started), so valw has to end it itself.
+pub fn release_ends_drag(dragged: Option<u64>, released_on: u64) -> bool {
+    dragged == Some(released_on)
+}
+
 /// `expired`: the thumbnail's timer fired while it was being dragged.
 pub fn after_drag(outcome: Outcome, expired: bool) -> AfterDrag {
     match (outcome, expired) {
@@ -142,6 +150,13 @@ mod tests {
         assert!(through_pipe("text/html", Path::new("/tmp/a.png")).is_err());
     }
 
+    #[test]
+    fn a_release_on_the_dragged_thumbnail_ends_the_drag() {
+        assert!(release_ends_drag(Some(3), 3));
+        assert!(!release_ends_drag(Some(3), 4), "another thumbnail");
+        assert!(!release_ends_drag(None, 3), "no drag going on");
+    }
+
     #[test]
     fn after_drag_decisions() {
         assert_eq!(after_drag(Outcome::Dropped, false), AfterDrag::Close);

src/host.rs

@@ -302,6 +302,10 @@ impl Host {
         let Some(drag) = self.drag.take_if(|d| d.source.inner() == source) else {
             return;
         };
+        self.finish_drag(drag, outcome, qh);
+    }
+
+    fn finish_drag(&mut self, drag: Drag, outcome: Outcome, qh: &QueueHandle<State>) {
         tracing::info!("drag-out {outcome:?}");
         drag.icon_viewport.destroy();
         drag.icon.destroy();
@@ -361,6 +365,13 @@ pub fn pointer(state: &mut State, events: &[PointerEvent], qh: &QueueHandle<Stat
             PointerEventKind::Release {
                 button: BTN_LEFT, ..
             } => {
+                let dragged = host.drag.as_ref().map(|d| d.thumb);
+                if dnd::release_ends_drag(dragged, host.thumbs[i].id) {
+                    tracing::info!("the compositor never took the drag over");
+                    let drag = host.drag.take().expect("checked above");
+                    host.finish_drag(drag, Outcome::Cancelled, qh);
+                    continue;
+                }
                 let t = &mut host.thumbs[i];
                 if t.release(x, y, qh) == Some(Action::OpenEditor) {
                     open_editor(&t.path);