Add debug assert, any open segment cannot have same/newer ID than unused

Author: timvisee

src/segment_creator.rs

@@ -80,6 +80,14 @@ impl SegmentCreatorV2 {
             .or(open_segment)
             .map_or(1, |s| s.id + 1);
 
+        // Any open segment must have lower ID than all unused segments
+        debug_assert!(
+            unused_segments
+                .iter()
+                .all(|s| open_segment.as_ref().is_none_or(|o| s.id > o.id)),
+            "open_segment must have lower ID than all unused_segments",
+        );
+
         let mut result = Self {
             dir,
             pending_segments: unused_segments,
@@ -245,4 +253,24 @@ mod tests {
 
         assert_eq!(entries.len(), 10 - 3 + 1); // open-3 existed, open-4 to open-9 created + open-10 created ahead
     }
+
+    #[test]
+    #[should_panic(expected = "open_segment must have lower ID than all unused_segments")]
+    fn test_segment_creator_v2_invalid_open() {
+        init_logger();
+        let dir = Builder::new().prefix("segment").tempdir().unwrap();
+
+        let segment = Some(OpenSegment {
+            id: 4,
+            segment: Segment::create(dir.path().join("open-3"), 1024).unwrap(),
+        });
+
+        let unused_segments = vec![OpenSegment {
+            id: 4,
+            segment: Segment::create(dir.path().join("open-4"), 1024).unwrap(),
+        }];
+
+        // Expected to panic, open segment cannot have same or higher ID than unused segments
+        SegmentCreatorV2::new(dir.path(), segment.as_ref(), unused_segments, 1024, 1);
+    }
 }