Fix panic with IdxRange size() method.

src/idxsets/idxrange.rs

@@ -28,11 +28,43 @@ impl IdxSet for IdxRange {
     }
 
     fn size(&self) -> usize {
-        ((self.0.end - 1) / crate::bits::bitfield::BITS + 1)
-            - self.0.start / crate::bits::bitfield::BITS
+        if self.0.end <= self.0.start {
+            0
+        } else {
+            let bitfield_end = (self.0.end - 1) / crate::bits::bitfield::BITS + 1;
+            let bitfield_start = self.0.start / crate::bits::bitfield::BITS;
+            bitfield_end - bitfield_start
+        }
     }
 
     fn intersect(&self, idx: &Bitfield) -> Bitfield {
         (*idx).clip(&self.0)
     }
 }
+
+
+#[cfg(test)]
+mod test {
+    use super::*;
+
+    #[test]
+    fn test_size_of_zero_length_idxrange() {
+        let zero_range = IdxRange(0..0);
+
+        assert_eq!(zero_range.size(), 0);
+    }
+
+    #[test]
+    fn test_size_of_single_length_idxrange() {
+        let zero_range = IdxRange(0..1);
+
+        assert_eq!(zero_range.size(), 1);
+    }
+
+    #[test]
+    fn test_size_of_short_idxrange() {
+        let zero_range = IdxRange(0..7);
+
+        assert_eq!(zero_range.size(), 1);
+    }
+}

src/types/entry.rs

@@ -96,10 +96,7 @@ where
         R: Debug,
     {
         self.get().or_else(|| {
-            panic!(format!(
-                "retriever: Entry::or_panic(): {:?} doesn't exist",
-                &self.id
-            ))
+            panic!("retriever: Entry::or_panic(): {:?} doesn't exist",&self.id)
         });
 
         self